Brake System Design Component Choice


    This section is meant to be a second chapter, expanding upon what was discussed in the Brake System Design Theory chapter.

    This is a discussion of the things to consider when deciding what components to choose when building a brake system.

    Expanding upon the most important things we learned in the previous discussion of Brake System Design Theory:

      There Are Three Ways To Increase Braking Force:
      • Increase brake caliper piston area.
      • Increase rotor diameter.
      • Increase brake pad friction coefficient.

      And

      Brake Bias Must Always Be Considered.
        The brake system must be balanced and built to provide the appropriate amount of braking force to the rear brakes to match the braking force of the front brakes. Modifying the brakes on one end of the car (IE: Front Big Brake Kit) while ignoring the brakes on the other end of the car, will result in a Brake Bias Problem (Brake Oversteer or Brake Understeer).

    The Parts of the Brake System
    Starting at the pedal and moving out from there

      Brake Master Cylinder
        The brake master cylinder is the hydraulic mechanism attached to the back of the brake pedal. The driver presses on the pedal, which pushes a piston down the bore of the brake master cylinder, and the fluid in the cylinder is forced out and down the brake lines and pipes, to the brake calipers to provide pressure and force to move the brake pads against the rotors.
        The brake master cylinder is the input end of the brake system. Most of the variables, such as changing the diameter or piston travel of the master cylinder, will do more to change the amount of effort required to operate the brakes, and the fluid capacity of the system, than change the amount of force pushing the brake pad against the brake rotor or the braking ability of the vehicle.

        The Geo Storm and Isuzu sister cars (Impulse and Stylus) uses a dual cylinder brake master cylinder with a .875 inch diameter. The single shaft has two pistons (one mounted in front of the other), which push fluid under pressure to two hydraulic circuits. Each of these two circuits operates one front and one rear brake, on opposite sides of the car (diagonal). The forward circuit of the master cylinder (toward the radiator) has one pipe exiting the side of the master cylinder that leads to the left front brake, and a second pipe exiting (through a residual pressure valve) which leads to the right rear brake. The rear circuit of the master cylinder (toward the brake booster) has one pipe exiting the side of the master cylinder that leads to the right front brake, and a second pipe exiting (through a residual pressure valve) which leads to the left rear brake. This system is designed to provide additional safety in case there is a leak in one of the circuits, the other two brakes will work temporarily, hopefully long enough for the car to be safely brought to a stop. This arrangement is typical of most modern passenger automobiles.

        The .875 inch piston diameter is in the middle of the range of sizes. It is common to a lot of cars that are larger and heavier than the Geo Storm and could be considered a little oversized for cars in this weight class.
        The important aspect is that the brake master cylinder capacity be matched to the brake caliper capacity. Using huge brake calipers with a relatively small master cylinder would not provide enough fluid movement to press the brake pads against the rotors and stop the car.

        The hydraulic systems work sort of like gears and levers. Changing the piston diameter on one end will change the required force to move the piston on the other end, and the amount of force the piston on the other end applies to pressing the pad against the rotor.
        Increasing the master cylinder diameter will increase the amount of fluid pumped through the line and the movement of the piston on the brake caliper, but it will also increase the amount of effort required to press the brake pedal. Stiffer pedal with shorter throw.
        Decreasing the master cylinder diameter will decrease the amount of fluid pumped through the line and the movement of the piston on the brake caliper, but it will also decrease the amount of effort required to press the brake pedal. Softer pedal with longer throw.

        As mentioned in the theory section, the relationship between brake master cylinder diameter and braking force is a little counterintuitive.
        A larger master cylinder will require more leg input to achieve the same pressure through the brake line. That is the variable just above the master cylinder diameter on the TCE Performance Brake Bias Calculator. This means that if the master cylinder diameter is increased from .875 inch diameter, to 1.0 inch diameter, then the driver will have to press on the brake pedal harder to achieve the same braking force. How much harder? 31% harder. An increase from 60 Lb. to 78.5 Lb.

      Residual Pressure Valve.
        Most brake systems have a residual pressure valve in the rear brake hydraulic circuit. This is often incorrectly identified as a proportioning valve.
        The rear brake lines are longer than the front brake lines, and this difference in length will cause a measurable loss of pressure between brake pedal use. When the brake pedal is released, the movement of the rotor past the brake pads (or drum past the brake shoes) presses the caliper (or slave cylinder) mechanism open to allow free movement of the wheels when the brakes are not in use. The amount the mechanism is opened must be controlled and minimized so that the brakes will fully engage the next time they are needed and the pedal is pressed. The residual pressure in the brake line resists excessive movement and allows the pads and shoes to release enough that the wheels will rotate freely, while keeping the pads in a ready position by preventing them from moving back too far. For the longer rear brake line circuit, the residual pressure valve maintains a minimum backpressure in the line to control the rear brake mechanisms and keep them primed for their next needed use.
        For rear drum brakes, a residual pressure valve set between 7 and 10 pounds pressure is normally used. For rear disc brakes, a residual pressure valve set at about 2 pounds pressure is normally used.
        The Isuzu sister cars with rear disc brakes use the same residual pressure valves as the Geo Storm and Isuzu cars with rear drum brakes. So these valves do not need to be changed when converting the car over to disc brakes. However, the older I-Mark and Spectrum use a higher pressure valve which is not compatible with rear disc brakes.

      Proportioning Valve.
        Most factory brake systems, as well as the Geo Storm and Isuzu sister cars, do not use a proportioning valve in the OEM brake system. Though people often confuse and misidentify the residual backpressure valve in the rear brake circuit as a proportioning valve.
        The factory brakes have been carefully designed (through careful choice of brake caliper piston size, brake disc diameter, and brake pad compound) to work in balance to match the weight distribution and weight transfer of the car in stock configuration, without the need to limit the pressure to any of the brake calipers.
        A brake proportioning valve is a pressure limiting device, typically used to fix a brake balance or biasing problem. These are normally used to reduce the braking force of the rear brakes and reduce braking oversteer when the rear brakes lock up too easily. Brake proportioning valves are also, though rarely, used to reduce the braking force of the front brakes (typically if a front big brake kit is paired with OEM rear brakes) and reduce brake understeer.
        An adjustable brake proportioning valve typically has a knob or lever which allows full hydraulic pressure through the line when set to zero, and can be adjusted or turned up to reduce hydraulic pressure through the line by up to around 60%. This really represents the only knob or easily adjustable item in the brake system, which can be changed or adjusted without dismantling or replacing parts of the brake system. This makes a brake proportioning valve an important tool for on-track adjustment of the brake system.
        Ideally, the braking system would be designed so that the rear brakes are able to slightly overpower the front brakes, and the proportioning valve can be set to the middle of its adjustment range to get the car balanced for normal conditions. Then the brake balance can be fine tuned slightly up or down to match the track, course, or pavement conditions, or changes that affect driving style and brake usage.
        In the event that a proportioning valve is used to fix a large brake imbalance problem, and the solution is to turn the valve all the way up and limit pressure as much as possible, this is a good sign that the brake system should be redesigned and adjusted on one end of the car or the other, either by reducing braking force (caliper piston size, rotor diameter, or pad compound friction coefficient) on the end of the car being turned down with the brake proportioning valve, or by increasing braking force on the opposite end.

        If a brake proportioning valve is used in a car with multi channel rear brakes, such as the OEM brake setup of the Geo Storm and Isuzu sister cars (two piston master cylinder, two circuits running diagonal), then the system will require one brake proportioning valve for each of the two separate rear brake lines, and those proportioning valves must be of decent enough quality level to provide matched and consistently accurate pressure settings for the separate valves. (Use a decent quality valve made with high enough standards that two valves set to the same point produce the same amount of pressure reduction).
        Wilwood and other manufacturers do not recommend using brake proportioning valves side by side like this, but they do admit that in the racing field, their products are successfully used in this un-recommended manner.

      Brake Calipers
        The brake caliper uses the pressurized brake fluid from the brake master cylinder, to press the brake pads against the brake rotor, in order to slow the car down. The brake rotors do not have any mechanism to release the pads from the rotor, and rely on the rotation of the rotor to move and push back at the caliper mechanism and move the brake pads away from the rotor to allow free movement of the wheels when the brakes are not being used.

        The Geo Storm front brakes use a single piston, sliding brake caliper (also called "floating" or "compound" calipers), with a 2.0 inch piston diameter. The rear brakes are drum brakes. Drum brakes are adequate for street use, but have several serious limitations. The drum assembly weighs considerably more than the comparable disc brake system. The larger volume of the drum can withstand and absorb more heat than a disc brake, but the drum does not cool easily or well. Availability of drums and shoes is limited to OEM and OEM replacement, without much, if any, ability to change the size of the drum or the type of shoe. And it takes some pretty serious math to calculate braking force for drum brakes. So for the purposes of this discussion, we are going to use the Impulse XS / Stylus XS rear disc brakes as a baseline to work from.
        The Impulse XS / Stylus XS rear brake caliper is a single piston, sliding brake caliper, with 1.25 inch piston, with a built in emergency/parking brake mechanism (combination caliper).

        Types of Brake Calipers
        (Some Work Better Than Others)
          Sliding Brake Calipers, also called Floating Calipers
          The OEM brake calipers of the Geo Storm (and Isuzu sister cars) are sliding calipers, the same design as used on most passenger cars. Sliding calipers usually have a single piston that is mounted on the back side of the brake assembly. The single piston presses against the back of the brake rotor. In order to provide force to squeeze both sides of the brake rotor, the sliding caliper is mounted on slide pins, and has a large cage assembly to hold the outer brake pad to the brake piston assembly. As the brake piston presses against the inner brake pad, it also pushes itself away from the brake rotor and pulls the outer brake pad into the outer face of the brake rotor. Sliding calipers are also commonly called "floating calipers" and "compound calipers" because the caliper "floats" within the brackets or cage assembly that it slides on, and the large number of moving parts and pieces fit the definition of the word "compound".
          Sliding brake calipers have fewer hydraulic parts and fewer precision parts, and are very cheap to make. They also have the additional advantage that they require very little precision for mounting and installation (inner and outer offset and clearance around the rotor), and can adapt to a large range of inconsistent manufacturing mistakes. This makes them ideal for assembly line installation on a car.
          Their main drawback is that they do not work very well. Braking force is not applied consistently or evenly because the caliper must press the inside pad against the back of the rotor in order to build force to pull the cage assembly and pull the outside pad into the outer face of the rotor. Examining the rotor will usually reveal uneven wear to the rotor, with more wear on the inside face than the outside face. The slide pins do not work very smoothly to begin with, and become sticky with neglect and age. The inside brake pad typically never fully releases and drags while the brakes are not being used. This negatively affects performance, fuel consumption, and wear.
          And because all of the moving parts are being actuated by a single piston on one side, the mechanism has a lot of slop. When the brake pedal is pressed, the piston has to move across a wider distance before the pad meets the rotor, and the brakes begin working. When the brake pedal is released, the mechanism has to move across a wider distance before the pads are no longer rubbing against the rotor. This results in excessive brake pedal travel, especially noticeable when using larger 2 1/8 inch and 2 inch single piston calipers.
          In terms of building a performance brake system, sliding brake calipers are not desirable and should be avoided. Upgrading from one poorly functioning sliding brake caliper to another poorly functioning sliding brake caliper is a waste of time.

          Fixed or Multiple Piston Brake Calipers
          Performance brake systems use fixed or multi piston brake calipers. These have become popular upgrades and options on factory vehicles. Brembo is probably the most common and recognizable brand name associated with upgrade and performance brake packages as original equipment on sports and performance cars. These are usually very conspicuous with large, aluminum, fixed, multi piston calipers on the front, and often the back of the vehicles.
          Fixed brake calipers are rigidly mounted to the spindle and have multiple pistons which are positioned on both sides of the brake rotor.
          Fixed calipers have more hydraulic parts, more parts that are made to a higher level of precision, and must be mounted with tight tolerances to match the position of the rotor. The caliper mounting bracket must be precise enough to keep the caliper from rubbing against the rotor while also keeping the caliper positioned correctly to press the brake pads against the rotor. All of these things make fixed calipers more expensive to make and install and less desirable for assembly line installation on a car. Hence the reason they are rare on production cars and typically a rather expensive upgrade option when offered at all.
          The justification for all of the added expense and difficulty is superior braking performance. The mechanism applies force evenly to both sides of the brake rotor. The brakes engage quickly and smoothly and disengage quickly and smoothly. Braking performance is more consistent. Because the mechanism releases the pad from the rotor smoothly, easily, and completely, there is no friction from a pad dragging against the rotor, and there is benefit to performance, fuel consumption, and wear. And because the clearances are tighter and there is no sloppy sliding mechanism, the pistons and brake pad only move a very short distance when the brake pedal is engaged, minimizing brake pedal travel, even for multi-piston calipers with larger diameter pistons.

          Fixed or multi piston calipers are available from a large number of aftermarket racing companies, and in a wide range of sizes. In addition to this, many specific caliper models are available in a wide range of piston sizes.

        Increasing Braking Force By Increasing Brake Caliper Piston Area.
        Remember that the goal of all this was to increase the braking force, and the only variable within the brake caliper that will increase braking force is to increase the brake piston area.
        The gear / lever relationship already discussed regarding the brake master cylinder size is similar on the business end of the system at the brake caliper.
        Increasing the quantity of the brake caliper piston area (size and/or number of pistons) will increase the force applied to the brake pads to press them against the rotors (increasing the braking force).
        Decreasing the volume of the brake caliper piston area (size and/or number of pistons) will decrease the force applied to the brake pads to press them against the rotors (decreasing the braking force).

        The Geo Storm (and Isuzu Impulse/Stylus) front brake caliper piston is 2.0 inches in diameter, or 3.142 square inches in area. The Impulse XS / Stylus XS rear disc brake caliper used as the base point to work from is 1.25 inches in diameter, or 1.227 square inches in area.
        Increasing the front braking force, without changing the rotor diameter, requires increasing that area by either using a single piston caliper with a piston larger than 2 inches, or a multi piston caliper whose area calculates out to be larger than 3.142 square inches.
        Replacing the OEM Geo Storm 2.0 inch piston caliper with another 2.0 inch diameter single piston caliper, or any multi piston caliper that calculates out to the same 3.142 square inches of piston area, will not change the braking force on the front brakes.
        The same for the rear, any caliper with a piston area of 1.227 square inches or less, on the same size rotor, will not increase the braking force.

        Again, care must be taken to make sure that the brake calipers are not oversized for the brake master cylinder fluid capacity, but there is a certain amount of flexible range to work within. And as mentioned, fixed, multi-piston calipers do not require as much fluid to apply the brake pad to the rotor as single piston sliding calipers, so upgrading to the better caliper allows the safe use of a larger piston area that will provide more braking force.
        Brake kit manufacturers offer front brake kits for cars with .875 inch diameter master cylinders with calipers with a piston area as large as 4.112 square inches. That would be a four piston caliper with four 1.62 inch diameter pistons (a hair less than a single piston sliding caliper with a 2.3 inch diameter piston). That is considerably larger than the OEM 2.0 inch front single piston sliding caliper.

        Returning to the TCE Performance Products Brake Calculator page, playing with the brake piston size illustrates just how much influence that this variable has on the braking force.
          The OEM front brake caliper has a 2.0 inch diameter piston, and yields a 2530 In.Lb. braking force (using the stock specs as previously discussed).
          Change that to a 2.125 inch diameter front piston and the front braking force increases to 2856 In.Lb. A 13% increase in braking force.
          Change that to a 2.25 inch diameter front piston, and the front braking force increases to 3202 In.Lb. A 27% increase in braking force.
          Try a four piston calipers. Enter 1.38 inch into the boxes for Piston 1 and Piston 2 (the opposing piston is not needed for the calculation), and the braking force is 2408 In. Lb. A hair below the stock caliper.
          Try a 1.5 inch four piston caliper, and the braking force is 2846 In.Lb. That same 13% increase in braking force of the 2.125 inch single piston caliper.
          And the next larger size four piston caliper at 1.62 inch results in a braking force of 3319 In.Lb. Just a little more than the 27% increase from the 2.25 inch single piston caliper.
        So there is a wide range of braking force across the range of usable caliper piston area that the brake master cylinder will support, with a step up in size to 13% more braking force, and a second step up in size to a 27% increase in braking force.

        A Caliper With a Range of Available Piston Sizes.
        This brings another concern to light, that of designing the brake system for flexibility. The OEM brake caliper on the front of the Geo Storm is available in one and only one piston diameter. Most OEM brake calipers are similarly limited and available in one and only one piston diameter. And like most OEM parts, they are made very specific to the vehicle, and are not interchangeable in mounting (bracket shape and bolt positions) or plumbing (hose attachment type and thread). Picking an OEM brake caliper from another automobile for use on a brake system (on a Geo Storm or any other car) severely limits the choices, flexibility, and adjustability of the braking system, basically to that one, single brake caliper. Once money is spent on making a bracket to attach it to the car, a custom hose to connect it to the hydraulic system, and pads to fit into the caliper, the decision is set in stone and the brake system is built around that one size caliper. If a calculation during the design phase, or the real world performance of that caliper does not match what is needed, then the entire caliper, bracket, hose, and pad assembly has to be removed, discarded, and a new assembly built from scratch, around another caliper, to change one simple variable that can be used to adjust the brake force and bias of the system: the brake piston area.
        As previously mentioned when discussing many of the fixed, multi piston aftermarket racing calipers are made in a wide range of piston sizes, all of which share the same caliper body, mounting pattern, brake pad, and hose fitting size. This means that the entire caliper can be easily swapped out for another caliper of with different sized pistons. The mounting is exactly the same. The brake pads are exactly the same. The entire operation is two mounting bolts, the brake hose, switching the pads from the old caliper to the new caliper, and bleeding the air out of the new caliper.
        Building a brake system around a readily available aftermarket racing caliper that is available in several different piston sizes, provides a wide range of flexibility. A simple caliper swap fine tunes the braking force up or down 13% or 27% (or more), without making a new mounting bracket, brake hoses, or buying new pads.

        An additional benefit to this is that if the caliper ever fails and needs to be replaced, an off-the-shelf aftermarket brake caliper, which requires no modification to install, will be readily available and quick to replace.
        An OEM caliper from another vehicle may be a challenge to source used, may require a rebuild to be made usable, and if it has to be modified to fit the vehicle, can turn a simple caliper replacement into a long, expensive, and labor intensive nightmare.

        Pad Size
        The choice of brake caliper will determine the size and shape of the brake pad and the range of brake pad friction compounds available.
        As mentioned in the previous discussion of Brake System Design Theory, the overall area of the brake pad does not affect the braking force. The only variable that affects braking force is the radial height. Basically the width of the swept surface where the pad meets the rotor (from the edge of the rotor to the bottom of the pad). The narrower this measurement is, the farther the center of braking force is from the axis of rotation, and the higher braking force is due to the mechanical advantage of the longer lever arm.
        The overall area of the pad has no affect on the braking force, and only determines how long it will take the pad to wear out.
        It is a good idea to choose a caliper with a pad area that is the same as, or slightly larger than the OEM brake pad. This will maintain or improve the replacement interval, or how often the pads wear out and must be replaced. And no one complains when improving performance also provides lower operating cost.
        So the important detail, when comparing calipers, is not to be confused by pad size. Remember that a large body caliper with a really tall radial height pad is actually going to decrease the braking force, compared to a narrow body caliper with a pad that has a small radial height that might look like a crescent shaped sliver.

        Pad Availability
        Farther along, we will cover brake pad compounds and their affect on braking force. At this point when considering choice of brake caliper, the only friction compound concern is making sure that there is a range of brake pad compounds available in the pad pattern that fits the caliper being considered.
        Most of the OEM, single piston, sliding calipers, have a very narrow range of pads available from aftermarket companies. A car that is not popular for racing or does not have a large following among car enthusiasts, is probably going to be limited to lower quality, lower performance, and lower friction coefficient pads ranging from extremely cheap replacements to higher quality ceramic pads. Most of these are going to be in the very low end of the friction coefficient range.
        A few of the more popular cars for racing, especially those popular in racing classes which require the use of OEM calipers and rotors, have a pretty wide range of available pad compounds from the low friction cheap pads well up into the high bite racing pads.
        Most of the aftermarket racing calipers have a wide range of available racing pads well into compounds that would be unsuitable for street use. But many of these aftermarket racing calipers are marketed for the street rod and hot rod market, and offer streetable pads that are at least in the mid and upper range of what can be used on the street. Conversely, there may be no selection of low friction pads available, for a racing caliper, at all.
        Custom brake pads can be made for just about any pad pattern, but are often very expensive, starting over $200, and with a narrow range of friction coefficients, typically aimed more for racing than for street use.
        Pad selection and the range of available brake compounds is an important consideration when selecting a caliper, because it will affect the available choices of what can be done to fine tune the braking balance and bias.

        Wheel Clearance
        Probably the biggest issue in choosing a caliper is going to be the clearance on the back side of the wheel.
        The combination of the rotor diameter and the size of the caliper body will determine whether or not the wheel hits the brake caliper, or can even be bolted onto the hub.
        The Geo Storm GSi uses 9.7 inch diameter front rotors and a single piston sliding caliper with a very tall sliding bracket and caliper fingers sticking out past the edge of the rotor, to hold the pad on the outside face of the rotor. Sliding calipers sacrifice a lot on clearance at the edge of the rotor (require a lot of clearance on the inside of the wheel rim). But sliding calipers have a pretty low profile on the outside face of the caliper (require less clearance on the back face of the wheel, around the mounting surface). The original brake system design for the Geo Storm was meant to fit within a 14 inch steel wheel. The rotor has a rather shallow offset. The OEM aluminum wheels have a lot more clearance around the inside of the wheel rim than the steel wheels, but do not have significantly more clearance on the rear face of the wheel around the mounting surface.
        Fixed or multi piston fixed calipers typically have very low clearance requirements around the outer edge of the rotor (allowing for the use of larger diameter rotors). But fixed calipers tend to take up a large amount of space between the outer rotor face and the inside of the wheel, around the mounting surface. Remember, the multi piston calipers have a piston(s) between the rotor and the wheel, mounted facing the outside face of the brake rotor, and that mechanism takes up a lot more space between the rotor and the wheel, than the cage and fingers of a sliding caliper. This means that multi piston, fixed calipers require more space exactly where the OEM wheels of the Geo Storm and Isuzu sister cars do not have it.
        Chances are that any upgraded brake system is going to require aftermarket aluminum wheels with as much clearance around the brake caliper as possible. Most likely a 15x7 inch racing wheel, which will allow the use of the common 195/50R15 and 205/50R15 racing compound tires.
        At the other end of the car, the rear brake rotor has a deeper offset, and will require less braking force than the front. This means that most of the clearance issues will be confined to the front brake caliper, rotor, and wheel choice.

        Parking / Emergency Brake.
        The emergency brake or parking brake can become a problem to overcome when designing a brake system. At the dawn of Automotive History, all cars had drum brakes on the front and the back. The emergency or parking brake was integrated into the rear brake drum, as a cable activated device to push the rear brake shoes against the rear brake drum. Disc brakes were introduced as front brakes, and later as rear brakes, creating an issue when it came time to put an emergency or parking brake mechanism into the rear brake assembly.
        The 70s rear wheel drive car solution was to make a small drum brake inside the rear disk, that would be cable actuated, and separate from the rear disc brake caliper. Many rear wheel drive cars use this type of brake, including the first generation Isuzu Impulse. The small drum built into the rear brake disc can be a pain to deal with when trying to change the rear rotor diameter, but the separate emergency / parking brake assembly eliminates any restrictions on the rear brake caliper choice, and allows the use of the more desirable fixed or multi piston brake calipers.
        For front wheel drive cars, automakers came up with a second strategy. A combination caliper was developed, which would be both hydraulically actuated, to work with the brake pedal, and cable actuated, to work with the emergency or parking brake lever. All of these combination brake calipers are sliding caliper type. Remember, sliding calipers do not work very smoothly or efficiently to begin with, and the addition of the parking brake mechanism means they drag and stick even worse than regular sliding brake calipers. This arrangement also severely limits the choice of direct replacement rear brake calipers to the narrow and poorly working group of combination brake calipers (reuse the original on a larger rotor, find a suitable caliper from another car, or one of the few aftermarket calipers designed for street rods).
        The easiest solution is to simply drop the emergency or parking brake from the system, use a fixed or multi piston caliper on the rear brakes, and ignore the fact that the car does not have an emergency or parking brake. This works well if racing class rules do not require an operable parking brake, or if the car is always parked on a flat surface. Otherwise, the only viable solution is to add a second dedicated mechanical caliper to the rear brakes and attach the mechanical caliper to the parking brake cable. This solution is common on exotic cars such as Lamborghini and Ferrari, and mechanical calipers are available from both Brembo and Wilwood for exactly this purpose.

      Rotors
        The brake rotor is the cast iron disk that the caliper pushes the brake pads against in order to produce friction to slow and stop the vehicle.

        The OEM rotors on the front of the Storm GSi are 9.7 inch in diameter. The original design was meant to fit within a 14 inch steel wheel. The rotor has a rather shallow offset.
        This front rotor is paired with a 10.1 inch diameter rear rotor on the back of the Impulse XS and Stylus XS, making for a rather unbalanced appearance. But the difference in the brake caliper piston size adjusts the front braking force up to what is needed to balance the braking bias with this seemingly backward combination of rotor sizes.

        As mentioned previously regarding caliper clearance, the combination of the caliper size, brake rotor, and clearance within the wheel, must be considered when choosing the brake system components.
        The desirable 15x7 inch aluminum racing wheel to fit the desired 195/50R15 and 205/50R15 racing compound tires, will limit the rotor size to about 11 inches. Any larger than that, and the caliper will start raking the tape weights, used to balance the wheels, off of the insides of the wheels. And for practical purposes, the larger the tighter the clearance between the rotor and caliper combination, and the inside of the wheel, the more difficult it is to change the wheels without scraping and scratching the calipers and insides of the wheels. (Especially at bleary eyed 5 AM, at the race track at the beginning of the racing day, and at an exhausted 5 PM, at the race track at the end of the racing day). Again, if the wheel requires tape weights on the inside of the rim, 11 inch rotors are probably going to push the caliper out far enough that the caliper will hit the tape weights.
        11 inch might be a practical upper limit for rotor size without causing excessive damage to the wheels and calipers during wheel changes.

        How Does Rotor Diameter Affect Braking Force?
        Once again, the goal of all of this is to increase braking force. Referring back to the TCE Performance Brake Calculator, the OEM Storm GSi setup with the 9.7 inch diameter and specs provided calculates out to 2530 In.Lb.
          Increasing the diameter out to an even 10 inch rotor, and the braking force increases to 2624 In.Lb. A 4% increase over stock.
          With a 10.5 inch rotor, the braking force increases to 2780 In.Lb. A 10% increase.
          With a 11 inch rotor, the braking force increases to 2937 In.Lb. A 16% increase.
          And with a 11.5 inch rotor, the braking force increases to 3094 In.Lb. A 22% increase.
        While these are not huge gains in braking force, it is important to increase the rotor size (at the front axle) to the maximum size that will fit (without creating a problem with wheel changing), because this variable combines with the other two variables (caliper piston size and pad coefficient of friction) to yield the braking force. And passing up 5-16% of the potential braking force by using an undersized rotor will just make it that much more difficult to pick up that braking force through caliper piston size and brake pad coefficient of friction.

        Rotor Thickness, Solid or Vented
        The brake rotor does two things. It provides a friction surface for the brake pad to press against, and it dissipates the heat caused by the pad rubbing across its surface. The volume of the rotor body and surface area are what determine its ability to dissipate heat. Excessive heat will cause the brake fluid to boil, causing brake fade and spongy brakes. Excessive heat can also cause the surface of the brake pad friction material to melt, which will cause brake fade and the melted brake pad material can stick to the rotor face, causing high spots, which are the source of what is incorrectly called warped rotors. Excessive heat can also be conducted to the hub and wheel bearing, causing failure of the wheel bearing and damage to the wheel hub.
        The thickness of the rotor determines the mass of the metal and how much material is available to absorb heat. Vented rotors have an air passage between the inner and outer steel friction surfaces, which provides additional surface area to radiate heat, and a cooling duct for air to flow through to carry that heat away. These are important considerations when building a brake system.
        Rotor thickness and cooling ability does not affect braking force, but does affect how hard the brake system can be pushed before overheating.

        The Storm GSi, and Isuzu sister cars, use a 22mm thick, vented, front rotor. The Impulse XS and Stylus XS used as a baseline for the brake system, use a 9mm thick, solid, rear rotor. Remember, the front brakes are doing almost 2 times the work of the rear brakes, and these cars are nose heavy without much weight on the rear axle. A solid rear rotor is more than enough to do the job. But it is important to make sure to use a vented front rotor.
        A front rotor that is thicker than 22mm would be able to withstand more braking heat, but, as mentioned regarding caliper clearance, the rotor offset is very shallow with no space to move the rotor more inboard. Any additional rotor thickness will mean less clearance on the inside of the wheel face, as the rotor face and caliper must be moved out to make space for that additional rotor thickness.

        One Piece Rotors vs. Two Piece Rotors
        OEM rotors are made of a single piece of iron, using the same material for the friction surface as is used for the mounting surface and structure. These are also often called fixed rotors. Because one piece rotors are made of one solid piece of metal, there is very little flexibility in fit, and they are made specific to each vehicle they are designed to fit. One piece rotors range in quality from OEM and decent quality aftermarket replacements, to extremely poor quality cheap replacements.
        Most aftermarket performance big brake kits, and some higher performance OEM brake systems, use two piece rotors. A cast iron ring is used for the friction surface, while an aluminum center hat is used for the mounting surface and the structure holding the rotor to the car. This design benefits from weight reduction by using lighter weight material for the mounting surface, and improved heat dissipation, because the aluminum will absorb and radiate heat away from the brake rotors more quickly. Replacement of worn out rotors can be less expensive, because the center hat can be reused and only the outer friction ring must be replaced. Two piece rotors offer the additional benefit of flexibility, because an outer ring of any given diameter and thickness, can be adapted to fit nearly any vehicle by making a different center hat to match the mounting and offset needs of the vehicle. The rotor friction rings are available in various sizes from numerous different manufacturers in the racing industry, and typically range from pretty good quality for the less expensive choices, to extremely high quality and excessively expensive items that are made for F1 racing.

        As has been previously mentioned, the Storm and Isuzu sister cars use a front rotor with a very shallow offset. Add to this the details of the bolt pattern, center bore (hubcentric ring) and thickness. These details make the rotor design rather unique. And the shallow space between the brake caliper mounting flanges on the inside face of the rotor, and the inner wheel face on the outside face of the rotor, provide little flexibility or leeway for adapting something to fit these vehicles.
        There are no direct bolt-on brake rotors in a larger diameter that can be swapped over from another vehicle, and used on a Geo Storm or Isuzu Impulse or Stylus. With all the variables of offset, bolt pattern, bore, and thickness, inexpensive and mass produced brake rotors for an existing automobile are simply too application specific to be adapted to a vehicle with the tight clearance and space requirements of a Geo Storm or Isuzu Impulse or Stylus.
        Keep in mind that brake rotors are made from cast iron and are subjected to extreme temperatures. It is not safe to weld a brake rotor, because the steel weld wire or rod will expand and contract at a different rate than the cast iron of the rotor, and this will cause stress fractures around any weld.
        Brake rotors are also manufactured to rather tight tolerances for balance and round, because they rotate on the car at the same speed as the wheels. Drilling and filling lug holes is a recipe for disaster.

        This leaves two piece rotors as the only viable option. Which means selecting the appropriate size rotor friction ring and making a center hat to adapt the ring for use on the car as a two piece rotor.

        The hat is the center piece that bolts to the rotor ring, and adapts the rotor ring to fit the vehicle. It is typically made of aluminum.
        There are several different methods for attaching the hat to the rotor, and these differences are important. Bolted refers to attaching the hat to the rotor with a nut and bolt placed through a round hole. The problem with bolted attachment is that it ignored the fact that cast iron and aluminum expand and contract at different rates when heated and cooled. Over time, the bolted style attachment method will typically loosen the bolts, become noisy, and require retightening to re-secure the rotor to the hat. For this reason, bolted is considered suitable only for racing vehicles which are serviced and inspected very frequently.
        Floating or Brembo Style refers to attaching the hat and rotor with a bolt threaded into a special fastener that has a cylindrical shaft over the bolt which extends through a slotted hole in the cast iron rotor. The slot is oriented perpendicular to the axis of rotation, and allows the hat and rotor to expand and contract independently without causing stress or damage to either or to the fasteners. The floating style of attachment is more desirable for street use, because the bolts holding the rotor to the hat remain tight and will not self-loosen.
        This difference between attachment methods is an important detail when shopping for, comparing, and designing hats for rotor rings. Despite the inherent characteristic of bolted rotors loosening and requiring frequent retightening, the vast majority of rotor rings available (especially the lower priced rotors) use this attachment method, and the makers and sellers are more than happy to sell and recommend these for street use without ever discussing or cautioning about their constant need to be retightened.

        Rotor rings are available in a pretty wide range of diameters, but pricing and choice is driven by demand. There are a lot of inexpensive rotors available in 12 inch diameter size, and larger. This is due to the popularity of brake kits for muscle cars and popular newer cars with larger sized wheels. Meanwhile, smaller rotor diameters are much more limited in availability and typically much more expensive. The few really high quality 10 and 11 inch vented rotors on the market seem to owe their existence to the smaller formula class racing cars, and they are correspondingly more expensive.

        Depending on how much the front braking force is increased, it may not be needed, or even desirable, to increase the rear brake rotor diameter. The 10.1 inch rear rotors of the Impulse XS / Stylus XS used as the baseline to work from for building a brake system, can be easily matched with 10 and 11 inch front rotors through the choice of a rear caliper with a larger piston area, and/or a brake pad with higher friction coefficient.
        Though if larger rear discs are required, friction ring rotors are available as solid rotors, which more commonly available, and are quite a bit less expensive than the 11 inch vented rotors for the front, and the task of making a center hat is the same as for the front.

        Cross Drilled vs. Slotted vs. Plain
        There has been a multitude written about the infinitesimal and microscopic performance differences between cross drilled, slotted, and plain rotors.
        The justification being that the holes or slots allow a way for gasses and dust to evacuate from between the pad and rotor (and water in the case of driving in the rain), and that the edge of the hole or slot will wipe a fresh braking surface away on the face of the pad each time the pad passes over a hole or slot. If anyone ever tried to test the performance difference between plain, drilled, and slotted rotors, the differences would be so small as to defy measurement, and much smaller than the margin of error for the test.
        The important thing to remember is that cross drilled became the appearance that is most associated with performance, while always providing the highest propensity of stress cracking. It is best to just avoid cross drilled rotors.
        Slotting, done correctly with shallow grooves, avoids most of the problems of cross drilling. If the desire is to squeeze every ounce of performance and retain durability, slotted is the best choice.
        Plain work just fine, they just lack the intimidation factor.

        A Word On Brake Rotor Quality.
        As mentioned, OEM replacement rotors can range from extremely poor quality cheap aftermarket replacements, to very good quality replacements made by recognized names. And racing rotor rings used in two piece rotor assemblies, can range from decent quality to F1 racing parts.
        The point of upgrading the braking system is to improve stopping power, which is going to increase the stresses and wear on all of the components in the system. Larger diameter rotors, larger calipers with higher clamping force, and more aggressive brake pad compounds, are all going to combine for higher wear rates on the brake rotors, if the driver makes use of the improved stopping ability of the car, and enjoys that improved stopping power frequently. Even if the car is not driven hard, if high friction racing pads are part of the recipe to get more braking force out of the system, the rotors are going to wear out more quickly. As much as half of that black dust coating on the wheels, that is so common when using high friction pads, is not ground up brake pad compound, but ground up cast iron rotor.
        There is a wide range in quality of brake rotors. From the alloy of the metal, to the heat treating and tempering, to cryo treatments that extend rotor life. With brake rotors, more money spent generally means a higher quality, longer service life, and a higher level of resistance to warping and cracking. Be aware that companies like Wilwood, known for making good quality calipers may, not have as high a reputation for the inexpensive rotors they sell. Look at some of the companies offering several different levels of brake kits, and they will probably describe their higher quality option with comments like some of our customers asked for better quality rotors that didnt wear out so fast, and/or were streetable, and/or didnt make noise from constantly loosening fasteners.
        Do some research and look through some internet message boards discussing the topic of brake rotor replacement frequency on cars regularly used for track day events. These are people who take their car out on a road course a half dozen, a dozen, or more times a year, and they will have lots of experience with brake rotor wear. It wont take much investigation to discover that the rotor rings in the $90-100 each price range get lots of complaints about wearing down to their minimum thickness in six or seven months of track day events, or less. And the $180-250+ each price range rotors last two or three years or longer.
        If the goal is building a trailer queen show car, or something to be hard parked at the neighborhood car meet, this is not an issue. But if the brake system is being built to be used, and used often, pay attention to the quality of the rotors and invest in something that lasts.

      Brake Pads
        Brake pads are available in a range of friction materials, called compounds. Changing the brake pad compound will make a small change in the braking force.
        The measurement of the level of friction a brake pad provides is called the coefficient of friction. The coefficient of friction ranges from .25 to .86. The material used to achieve this range of friction has limitations and compromises in cost, noise, dust, and wear.
        The OEM pads on most passenger cars were chosen to provide adequate stopping power for the car in stock form, as well as concerns for low cost, long service life, and low dusting. Manufacturers will often compromise for better performance on their more expensive performance oriented models, accepting a reduced service life, higher cost, and more dust, for increased stopping power. This is why many German luxury cars seem to always have black front wheels and owners who complain constantly about how dirty their wheels get and the cost of constantly replacing front brake pads.
        With really aggressive racing pads, there are additional concerns. Many of these pads are designed to withstand and/or operate in very high temperature ranges, where normal pads would have melted and ceased working to slow the car. The compromise is that they provide little or no friction when they are cold and do not begin working until they have reached very high temperatures. As a result, most of these really aggressive racing pads are unsuitable for use on the street.
        There are also pads designed for endurance racing, which provide more middle range stopping power, but are specifically designed for the extreme high temperatures of endurance road racing. These have been designed to withstand extremely high temperatures and also do not work until they are very hot, making them unsuitable for street use.
        Care must be taken when comparing brake pads not to rely solely on the coefficient of friction number, and also to consider the heat range and intended use.

        So there is a lot of compromise involved in choosing a brake pad compound:
        Milder pads with lower coefficient of friction deliver less noise and dust. Wilder pads with higher coefficient of friction are noisy, squeal loudly, make a lot of dust, cover the wheels with gritty black powder, and often eat the brake rotors quickly.
        Milder pads are normally at or close to their peak friction at ambient air temperature. Extremely high friction racing pads do not reach their high friction potential until they are very hot, as in several hundred degrees. That means that the cold racing pad feels dull does not provide much bite for the first several times the brake pedal is pressed, and only comes up to operating temperature after several hard brake applications, as in a couple hot laps on a race track. These race pads are useless for panic stops or normal driving situations. They are intended for use on a vehicle where the driver is constantly switching between full throttle and full braking and pushing the car to its physical limits in order to achieve the quickest lap time on a race track. This is one of the primary reasons that these racing pads are not recommended for use on a street car.

        Types of Pads
        OEM pads, as previously mentioned, were chosen by the vehicle manufacturer to provide adequate braking force while minimizing dust, wear, noise, and cost.
        Autocross or Performance Street pads are intended to provide better initial braking bite and stand up to more abuse and heat, while trading for some additional dust, wear, noise, and cost.
        Circuit and Dedicated Race pads are intended to provide significantly more braking power and take a great deal more abuse and heat and essentially compromise everything by wearing out quickly, making huge amounts of dust, eating rotors quickly, making lots of noise, and costing as much as several hundred dollars per set. A set of pads might only last for a single 20 minute racing session before requiring replacement. These are the pads people describe as not working until they get up to temperature and wont stop the car well until the second or third high speed braking action gets the rotors and pads hit enough to work properly.
        Endurance Racing pads are intended to withstand more abuse and heat over longer racing duration, but provide a lower level of consistent braking power over a longer duration of heat and abuse.

        Also take into consideration that there may be limited availability of pad compounds in the specific pad pattern to fit a given brake caliper.
        The Geo Storm shares the front brake pad pattern with the first generation Mazda Miata. The Miata is a relatively popular track car, and has a pretty wide variety of brake pad compounds to choose from, ranging from very low friction, cheap aftermarket pads (~.25), to very high friction and expensive race pads (~.54+).
        Conversely, the rear brake pads for the Impulse XS and Stylus XS used as the baseline for building a brake system, have an extremely limited range of available pad compounds, because this pad pattern is not shared with any other vehicle. Obtaining a racing pad for the rear brakes basically requires finding a pad maker who is willing to make custom pads, and custom ordering pads at a premium cost.

        A lot, of aftermarket racing calipers, have a wide selection of expensive and high friction race pads to choose from, but the range to choose from often excludes the cheap, low friction OEM replacement pads that make up the lower end of the spectrum. Pads for aftermarket racing calipers tend to be in the higher friction and more expensive range, as that is what is in demand. This can be an issue when trying to resolve a brake bias issue that requires a lower friction pad to reduce braking force. The lack of cheap, low friction pads knocks the range of choices in half, with a minimum CF around .38.

        Something to devote serious consideration to is brake noise. Higher friction pads make a lot of noise. Anything above about .45 is going to make noise and as it approaches .5 it will start to sound a lot like a train whistle every time the car is slowed from speed to stop at a traffic light.

        Referring back to the TCE Performance Products Brake Bias Calculator, changing the brake pad compound really makes a very small difference in braking force.
        Consider that the range of friction coefficients for streetable performance pads is about .35 to .45.


        Referring back to the TCE Performance Brake Bias Calculator, the OEM Storm GSi front setup with the estimated stock pad at .30 cf and specs provided calculates out to 2530 In.Lb.
          Change the pad coefficient to .35, and the front braking force increases to 2951 In.Lb.
          Change the pad coefficient to .40, and the front braking force increases to 3373 In.Lb.
          Change the pad coefficient to .45, and the front braking force increases to 3795 In.Lb.
          Change the pad coefficient to .50, and the front braking force increases to 4216 In.Lb.

        The practical range of .35 to .45 will only produce about 18% change in the braking force. This is limited to the ability to find a pad of the desired friction coefficient available for the caliper being used. And it means sacrificing quiet for noise, clean for dusty, and long rotor and pad life for more frequent pad and rotor replacement. It is not an overly effective method of significantly changing the braking force in large increments. It is certainly much less effective than changing the brake caliper piston size, and severely limited by the choice of available pad compounds within the usable range.

        So this variable is more effective for making smaller changes in brake pad friction coefficient for smaller scale changes in braking force.


        If at all possible, the best strategy for a street driven car is to set the braking force by selecting a brake caliper piston size and a brake rotor diameter that will provide the needed braking force while using relatively mild brake pads. This will provide superior braking with lower ongoing brake pad replacement cost, less wear and longer life of those brake pads, less dust and mess on the wheels, and less noise from the brakes.

        For a dual purpose car that is street driven and also used on the track, following the above strategy and then supplementing a set of racing brake pads for track use if a higher temperature range is needed, provides the widest flexibility.

        For a dedicated race car, where noise and dust are not a consideration, the best strategy is to determine the heat range that the brakes will be operating at, and select a pad compound that will withstand (survive and operate correctly within) that level of heat. Then calculate out the braking force for the brake pad friction coefficient and rotor diameter being used, and select a caliper piston size that will yield the required braking force.

        Deciphering OEM and OEM Replacement Pad Friction Coefficient Codes
        OEM and OEM Replacement brake pads are marked with a multi-digit code which includes two digits stating the friction coefficient at 200 degrees Fahrenheit and 600 degrees Fahrenheit. The two digits indicating the friction coefficient use a code set by the Society of Automotive Engineers (SAE) Standard J866. The first digit indicates the friction coefficient range at 200 degrees Fahrenheit, and the second digit indicates the friction coefficient range at 600 degrees Fahrenheit. So, while the code does not state the exact friction coefficient, it does provide some indication about the torque curve, meaning if the pad bits more or less as temperature is increased, or if it stays within the same range across this temperature range.

        SAE J866 Friction Coefficient Code
        Code Letter Friction Coefficient Range

        C

        Up to 0.15

        D

        Over 0.15 up to 0.25

        E

        Over 0.25 up to 0.35

        F

        Over 0.35 up to 0.45

        G

        Over 0.45 up to 0.55

        H

        Over 0.55

        Z

        Unclassified



        This code will be either printed in paint on the edge of the friction compound, or printed in paint or stamped into the metal on the back of the brake backing plate.
        As stated, these rating ranges are a little vague, but this code does provide some comparison between two different pads and allows to at least some comparison of friction level to determine if one is similar, less, or more, than the other.
        This code system is also used on a lot of the performance oriented upgrade pads intended for street use. But the code is not very commonly used on racing brake pads which are intended for track use.

        Looking at the OEM pads for the Geo Storm (front) and Isuzu Impulse, Stylus, and Asuna Sunfire, the friction coefficient code within the longer code has the letters "EE". This indicates that the OEM pads for these cars are .25-.35 at 200 degrees Fahrenheit and also at 600 degrees Fahrenheit.

        SAE J866 Friction Coefficient Code Footnotes


        Brake Pad Compound Index
        The following is a semi-organized list of brake pad compounds arranged in descending order of friction coefficient at ambient air temperature or at the temperature where the pad begins to function properly. These friction coefficient ratings were found on manufacturer's websites and from various internet forum discussions. Be aware that several racing brake pad manufacturers flatly refuse to publish the friction coefficient ratings of their products.
        Every effort has been made to maintain accuracy and verify from multiple sources.
        Manufacturer claimed specs (when available) have been given the greatest weight.
        Consult the footnoted sources below the chart to verify the data.
        This list is for rough comparison only.
        Consult other sources to study any details and contact the manufacturer before making any decisions based on this data.
        A graph showing the increase or decrease in friction coefficient across the range of temperature operation is extremely useful, and can be found for some of the pads in the footnotes below the chart.

        Do not count on every brake pad manufacturer to offer any or all of their brake pad compounds for every single OEM caliper brake pad pattern or every racing caliper brake pad pattern. Before making any spending decisions, check to make sure the desired pad is offered for the desired caliper.

        Brake Pad Compound Index
        Pad Compound Coefficeint of Friction Themperature Range Use and Notes

        Hawk DTC-70

        .80-.86

        400-1600F

        Race only, Trans Am, Formula, CART, prototype racing.

        Cobalt XR1

        ~.80+*

        50?-1600F

        Racing.
        * Based on the average of the specs of the pads Cobalt states are comparable to their pad.

        Hawk HT14

        .74-.84

        300-1400F

        Race only, Trans Am, Formula, CART, prototype racing.

        EBC Bluestuff NDX

        .75

        ?-1832F

        Intermediate grade Trackday pads.
        (drops off with heat, .45@550, .42@800)

        Hawk HT10

        .72-.79

        300-1300F

        Race only, Formula, sports racers.

        Hawk MT-4

        .69-.74

        400-1200F

        Race only.

        Hawk DTC-60

        .68-.77

        400-1600F

        Race only, Trans Am, Formula, CART, prototype racing.

        Cobalt XR2

        ~.66-.72*

        50?-1600F

        Racing.
        * Based on the average of the specs of the pads Cobalt states are comparable to their pad.

        Carbotech XP12

        .65-.67

        250-1850F

        Track.

        Performance Friction Compounds 01

        .65

        167-1400F

        Track.

        Raybestos ST43

        .65

        ?-1400F

        Track.

        Cobalt Friction Spec VR

        .64

        50?-1600F

        Track

        Carbotech XP10

        .63-.65
        /
        (also cited as .60)

        200-1475F

        Track

        Carbone Lorraine RC8

        .60

        ?-1800F

        Track, Nascar, WRC racing.

        Hawk Black

        .59-.64

        100-900F

        Race only, light sedans, Formula, sport racers.

        Endless S580

        .58-.79
        /
        (also cited as .45-.60)

        572-1652F

        Advanced racing pad, mid to heavy weight cars, Super GT racing.

        Carbotech XP8/Panther

        .58 -.60

        200-1250F

        Track, open wheel and sports racers.

        Endless S330

        .55-.75
        /
        (also cited as .55-.65)

        572-1652F

        Advanced Racing, mid to heavy weight cars, Syper GT, GT3, and stock car racing.

        Hawk Blue

        .55-.72

        100-1200F

        Extremely popular SCCA club racing pad.

        Wilwood Compound A

        .55-.68

        100-1300F

        Race only, road course, sprints, oval.
        (drops back to .64 after 500)

        Hawk DTC-30

        .55-.67

        100-1200F

        Race only.

        Dixcel RD Type

        .55-.60

        F

        Autocross, Drift, Rally, Dirt Trial.

        Hawk 10

        .55

        300-1300F

        Racing, sedans, Formula, sports racers.

        Wilwood Compound H

        .54-.59

        100-1300F

        Race only, endurance racing.

        Carbotech Panther Plus / AX6

        .54

        50-1000F

        Autocross.

        Wilwood Compound J

        .53-.58

        100-1300F

        Race only.
        Has a reputation among the Pro-Touring community as a "Bad-To-The-Bone" autocross pad.

        Wilwood BP-30

        .52-.62

        100-1300F

        Race only.

        Hawk Blue 9012

        .52

        100-1200F

        Circuit, club racing.

        Pagid RST 1

        .51-.55

        212-1292F

        Rally, sprint, and stock car.

        EBC Orangestuff

        .50
        /
        (.50-.63)

        F

        For medium/longer duration race use.
        (increases with heat, .60@550, .63@800)

        Pagid RS15 Gray

        .50-.62

        239-1472F

        Racing.

        Acre Dripa

        .50-.60

        50-932F

        Race Only, Circuit, Drift.

        Endless Drift

        .50-.60

        F

        Drifting.

        Endless N30C

        .50-.60

        302-1472F

        Rally.

        Project Mu Comp-B for Gymkhana; Rear Metallic

        .50-.60

        F

        Competition, gymkhana.

        Porterfield R4-1

        .50 -.60
        /
        .56 Average

        200-1400F

        Racing; Vintage, Formula, Autocross.

        Project Mu D1 spec

        .50-.55

        32-716F

        Competition, drifting.

        Porterfield R4

        .50 Average
        /
        (also cited as .485)

        0?-1400F

        Full race compound.

        Acre PC3200

        .5

        50-1472F

        Semi-Street through 2 and 12 hour Endurance Racing.

        Mintex M1177

        .5+

        212-1292F

        Racing.

        Carbone Lorraine RC6

        ~.50

        ?-1800F

        Street/track.

        Wilwood Compound B

        .49-.63

        100-1300F

        Race only, club racing, rally, autocross.

        Cobalt XR3

        ~.49-.55*

        50?-1600F

        Club racing.
        * Based on the average of the specs of the pads Cobalt states are comparable to their pad.

        Project Mu Comp-B for Gymkhana; Rear

        .48-.60

        F

        Competition, gymkhana.

        Project Mu D1 spec EXTREME

        .48-.59

        212-1022F

        Competition, drifting.

        Hawk HP+

        .48-.56
        /
        (also cited as
        .45-.50)

        100-800F

        Streetable, circle track.

        Winmax W7

        .48-.53

        212-1562F

        Rally and circuit racing.

        Pagid RSL 1

        .48-.51

        212-1292F

        Endurance racing.

        Pagid RSH 29E

        .48-.51

        212-1292F

        Historic racing.

        Pagid RSC 1

        .48-.50

        212-1292F

        For ceramic composite discs.

        Carbone Lorraine RC6E

        .48

        ?-1800F

        Street/track, endurance.

        Mintex M1166

        .48

        212-1292F

        Motorsport, rally, circuit.

        Winmax ARMA Circuit AC4

        .47-.52

        572-1562F

        Racing, circuit.

        Winmax ARMA Rally AR3

        .47-.52

        50-1472F

        Racing, rally.

        Ferodo DS1.11(W)

        .47-.49

        392-1292F

        Touring Car, GT, Single Seat.
        Average .46 over temperature range.

        Mintex F4R

        .47 ?

        F

        Racing.

        EBC Greenstuff

        .47 Descending
        /
        (also cited as .46)

        32-1112F

        High performance street.
        Peak friction at room temperature, falls steadily to .40 at it's maximum temp of 1112F.
        EBC has the sketchiest friction data provided in three conflicting forms. 1. A statement of initial friction and friction at two temperatures. 2. A list of comparable brake pads from other manufacturers, each set averaging a .5 friction coefficient. 3. A chart.

        Endless N05S

        .46-.53

        572-1472F

        Dedicated racing pad, mid to heavy weight cars, rally and sprint racing.

        Pagid RST 3

        .46-.52

        212-1292F

        Rally, sprint, and stock car.

        Cobalt XR4

        ~.46-.52*

        50?-1600?F?

        Autocross.
        * Based on the average of the specs of the pads Cobalt states are comparable to their pad.

        Pagid RSH 3

        .46-.52

        212-1292F

        Historic racing.

        Porterfield R4-E

        .46 Average
        /
        (also cited as .485)

        0?-1400F

        Endurance race compound.

        Mintex F1R

        .46 ?

        F

        Racing.

        Carbonetic R-Spec

        .45-.60

        392-1472F

        Race.

        Project Mu RSR02

        .45-.58

        F

        Competition, circuit sports.

        Hawk DTC-15

        .45-.57

        200-800F

        Race only.

        Endless N05U

        .45-.53
        /
        (also cited as .43-.48)

        572-1472F

        Dedicated racing pad, mid to heavy weight cars, rally and sprint racing.

        Endless W007

        .45-.50
        /
        (also cited as .40-.55)

        572-1562F

        Carbon ceramic brake pad, circuit use only.

        Endless ME20 / CC40

        .45-.50

        302-1472F

        Aggressive street/track pad, mid to heavy weight cars.

        Pagid RSL 2

        .45-.49

        212-1292F

        Endurance racing.

        Dixcel Z Type

        .45-.49

        32-1562F

        Fast Road, Autocross, Circuit, Dirt Trial.

        Winmax ARMA Circuit AC3

        .45-.48

        572-1472F

        Racing, circuit.

        Winmax W6

        .45-.48

        392-1472F

        Tarmac rally.

        Pagid RSC 2

        .45-.47

        212-1292F

        For ceramic composite discs.

        Acre PC2600

        .45

        50-1382F

        Semi-Street through Endurance Racing for Porsche and Skyline.

        Carbotech Bobcat / 1521

        .45

        50-800F

        High performance street.

        Ferodo DSUNO(Z)

        .44-.50

        392-1292F

        Touring Car, GT, Single Seat, Rally.
        Average .48 over temperature range.

        Mintex M1155

        .44

        100-1112F

        Sports road and club rally, longer duration.

        Mintex F6R

        .44 ?

        F

        Racing.

        Mintex M1144

        .44-46
        /
        (also cited as .38)

        50-932F

        Sports road and light track day.

        Project Mu HC+

        .43-.58

        32-1472F

        Street sports.

        Project Mu HC+ 800

        .43-.58

        32-1472F

        Street sports. Assembled in Thailand, export market only.

        Pagid RS 14

        .43-.52

        212-1292F

        All around racing.
        Good initial bite.

        Endless N35S / CC43

        .43-.49
        /
        (also cited as .40-.43)

        572-1472F

        Dedicated race pad, mid weight cars, GT and rally racing.

        Winmax ARMA Street AT3

        .43-.48

        50-932F

        Street performance. Organic.

        Pagid RS5

        .43-.48

        212-1292F

        Racing.

        Dixcel Specom-Alpha

        .43-.48

        F

        Super GT and Formula Racing.

        Pagid RSC 1

        .43-.45

        212-1292F

        For ceramic composite discs.

        Project Mu Racing 999

        .42-.59

        392-1472F

        Racing, GT racing.

        Project Mu Club Racing RC09

        .42-.55

        F

        Racing, circuit. Export market only.

        Ferodo DS3000(R)

        .42-.52

        392-1202F

        Racing, touring car, rally, Group N, single seat, hill-climb.
        Average .48 over temperature range.

        Pagid RST 2

        .42-.49

        212-1292F

        Rally, sprint, and stock car.

        Wilwood BP-10

        .42-.46

        100-900F

        Street and strip, hot rods and muscle cars. Gradual increase in bite with heat.
        Flat response and good cold bite makes this a good choice for autocross.

        Project Mu HC-CS

        .41-.50

        122-1472F

        Street sports.

        Mintex F2R

        .42 ?

        F

        Racing.

        EBC Yellowstuff

        .41-.59

        212-1652F

        Track, rally, sprints, shorter duration races.
        EBC has the sketchiest friction data provided in three conflicting forms. 1. A statement of initial friction and friction at two temperatures. 2. A list of comparable brake pads from other manufacturers, each set averaging a .5 friction coefficient. 3. A chart.

        Project Mu RSF01A

        .41-.49

        392-1652F

        Competition, circuit sports.

        Pagid RSL 29

        .41-.44

        212-1292F

        Endurance racing.

        Pagid RS 44

        .40-.46

        212-1292F

        All around racing.
        Medium initial bite.

        Pagid RS 42

        .41-.44

        212-1292F

        All around racing.
        Flat curve at .41 mu through 572 F.
        Medium initial bite.

        Pagid RSH 42

        .41-.44

        212-1292F

        Historic racing.
        Flat curve at .41 mu through 572 F.
        Good cold friction.

        Project Mu Racing 777

        .40-.55

        572-1472F

        Racing, circuit, sprints and semi-endurance.

        Endless Pro Drift

        .40-.50

        F

        Drifting.

        Pagid RS19 Yellow

        .40-.49

        356-1292F

        Endurance racing compound.

        Pagid RS29 Yellow

        .40-.49

        356-1292F

        Endurance racing compound.

        Pagid RS4-2 Blue (RS42)

        .40-.46
        /
        (also cited as
        .40-.44)

        248-1112F

        Medium friction racing compound. Formula racing.

        Wilwood Compound E

        .40-.47

        100-1000F

        Performance street and drag racing.
        Relatively flat response and good cold bite makes this a good choice for autocross.
        This pad provides more friction than the BP-10 between 300 and 700F

        Endless CCRG

        .40-.45

        122-1472F

        Street and Track.

        Endless W003

        .40-.45

        392-1562F

        Circuit, sprint.

        Endless W008

        .40-.45

        392-1562F

        Carbon ceramic brake compound, dual performance street and track.

        Dixcel RA Type

        .40-.45

        392-1652F

        Circuit.

        Endless W005

        .40-.43

        F

        Carbone Lorraine RC5+

        .40-.43

        ?-1800F

        Street/track, track day.

        Dixcel Specom-Beta

        .40-.43

        F

        Endurance and Super Taikyu.

        Ferodo DS2500(H)

        .40-.43

        68-932F

        Track day & light race use.
        .42 average over temperature range.

        Winmax W5

        .40-.43

        212-1382F

        Tarmac rally.

        Pagid RSL 19

        .40-.42

        212-1292F

        Endurance racing.

        Pagid RST 4

        .40-.42

        212-1292F

        Rally, sprint, and stock car.

        Axxis Ultimate

        .40

        50-900F

        High performance street.

        Endless Premium Compound

        .40

        32-932F

        High performance street for European car applications.

        Porterfield R4-S

        Up to .41
        /
        (also cited as .40)

        0-1100F

        High Performance Street.

        Acre N-Zero

        .39-.66

        50-1472F

        Street Legal Modified and Race, Rally, Gymkhana.

        Project Mu Racing N+

        .39-.48

        212-1472F

        Racing, extreme circuit, linear response.

        Dixcel M Type

        .39-.44

        32-932F

        Street, Fast Road.

        EBC Redstuff

        .39-.44

        32-1382F

        Performance street, rally, track.
        EBC has the sketchiest friction data provided in three conflicting forms. 1. A statement of initial friction and friction at two temperatures. 2. A list of comparable brake pads from other manufacturers, each set averaging a .5 friction coefficient. 3. A chart.

        Winmax ARMA Circuit AC2

        .39-.43

        212-1382F

        Racing, circuit.

        Winmax ARMA Endurance AE1

        .39-.43

        572-1472F

        Racing, endurance.

        Winmax ARMA Rally AR2

        .39-.43

        122-1382F

        Racing, rally.

        Pagid RS4-4 Orange

        .39-.43

        284-1202F

        Touring car racing compound.

        Acre Formula 800C

        .38-.65

        50-1472F

        Race Only.

        Carbonetic C-Spec

        .38-.62

        ?-932F

        Street and race.

        Acre Pro-Race / Racing-Pro

        .38-.58

        482-1472F

        Racing Only. N1 through Semi-Endurance.

        Wilwood BP-20

        .38-.55

        100-1100F

        Street and track, track day. Steeper increase in bite with heat. Passes BP-10 at 375 degrees.
        The steeper slope of friction increasing with temperature makes this pad less desirable for autocross.

        Project Mu Comp-B for Gymkhana; Front

        .38-.49

        32-842F

        Competition, gymkhana.

        Endless Super Street Y SS-Y

        .38-.48

        32-752F

        Standard street performance.

        Ferodo FER4003(C)

        .38-.50

        392-842F

        Formula Racing.
        Average .46 over temperature range.

        Wilwood Compound Q

        .38-.47

        100-780F

        Street, moderate performance applications.

        Endless MXRS

        .38-.48

        122-1292F

        Street.

        Endless Super Street S SS-S

        .38-.45

        32-896F

        Standard street performance.

        Endless CC-A

        .38-.45

        122-932F

        Street.

        Winmax ARMA Street AT2

        .38-.43

        50-842F

        Street performance. Organic.

        Dixcel R01 Type

        .38-.43

        392-1652F

        Circuit.

        Endless N03W

        .38-.42

        F

        Dedicated race pad, light and mid weight cars.

        Winmax WE1

        .38-.42

        572-1292F

        Endurance racing.

        Endless MX72

        .37-.47
        /
        (also cited as
        .40-.50)

        122-1292F

        Aggressive street/track, dual performance street and track.

        Endless NS97

        .37-.43

        32-932F

        Advanced street performance.

        Winmax ARMA Circuit AC1

        .37-.40

        122-1202F

        Racing, circuit.

        Winmax W4

        .37-.40

        122-1202F

        Gymkhana, circuit racing, gravel rally.

        Winmax ARMA Rally AR1

        .37-.40

        50-1202F

        Racing, rally.

        Project Mu Type NS

        .37-.40

        ?-752F

        Street performance.

        Project Mu Type NS 400

        .37-.40

        F

        Street performance. Assembled in Thailand, export market only.

        Winmax ARMA Sports AP3

        .37-.39

        50-1382F

        Street performance. Semi-Metallic.

        Acre Dustless-Real

        .36-.49

        50-932F

        Street.

        Cobalt XR5

        ~.36-.44*

        50-1600?F?

        Recommended for rear axle of FWD vehicle with rear lockup issues. Bite trails off with heat.
        * Based on the average of the specs of the pads Cobalt states are comparable to their pad.

        Acre Formula 700C

        .35-.58

        50-1292F

        Race Only.

        Hawk HPS

        .35-.54
        /
        (also cited as .40)

        100-700F

        High Performance Street, autocross.

        Acre Light-Sport

        .35-.50

        50-932F

        Street.

        Acre ZZC

        .35-.50

        50-1472F

        Street.

        Hawk DTC-05

        .35-.48

        100-700F

        Dirt Track Racing.

        Acre Euro Street

        .35-.45

        50-806F

        Street.

        Acre Street Fighter

        .35-.45

        50-806F

        Street.

        Endless SS-H / SSH (CC-RG?)

        .35-.42

        32-1112F

        High performance street pad, extremely quiet, Brembo caliper applications only.

        Endless SNP

        .35-.41

        32-752F

        Dixcel Carbon Metal Series R15C

        .35-.40

        F

        GT, Endurance, Touring Car.

        Project Mu Racing Sintered

        .35-.40

        662-1832F

        Racing, endurance racing.

        Pagid RS7-1

        .35

        F

        Flat bite curve through 500 degrees Celsius. Pad designed for use on rear axle and available only in sizes used on rear axles. Extremely limited applications and declared "obsolete".

        Project Mu Type NS-C

        .34-.38

        32-752F

        Street performance.

        Winmax W3

        .34-.37

        50-1112F

        Gymkhana, circuit racing.

        Winmax ARMA Sports AP2

        .34-.36

        50-1292F

        Street performance. Semi-Metallic.

        Project Mu Racing N-1

        .33-.45

        F

        Racing, low-to-middle speed racing in light vehicles.

        Endless PB

        .33-.40

        32-932F

        Aggressive street, European models only.

        Endless ME22 / CC38

        .33-.40

        300-1472F

        Aggressive street/track, mid to light weight cars.

        Winmax ARMA Endurance AE2

        .33-.37

        572-1562F

        Racing, Endurance.

        Winmax ARMA Street AT1

        .33-.35

        50-752F

        Street performance. Organic.

        Acre Compact

        .32-.46

        50-806F

        Street.

        Project Mu B Spec

        .32-.45

        32-932F

        Street sports.

        Carbonetic S-Spec

        .32-.42

        ?-932F

        Street.

        Winmax W2

        .32-.35

        50-932F

        Street performance.

        Dixcel Carbon Metal Series R21S

        .32-.35

        F

        Endurance. For Rear Axle.

        Dixcel Carbon Metal Series R30S

        .32-.35

        F

        Endurance.

        Acre Formula Sport

        .30-.48

        F

        Autocross, Track Day.

        Endless M- Sports SS-M / SSM

        .30-.40

        32-986F

        High performance street pad, low dust.

        Dixcel Carbon Metal Series R23C

        .30-.35

        F

        Endurance.

        Endless Type-R

        .30-.35

        122-1202F

        Street and Track.

        Winmax ARMA Sports AP1

        .30-.33

        50-1112F

        Street performance. Semi-Metallic.

        Endless MA45B

        .30-.33
        /
        (also cited as .30-.35)

        572-1472F

        Endurance racing.

        Dixcel Carbon Metal Series R26S

        .30-.33

        F

        Endurance.

        Project Mu Racing N-1 FFR

        .29-.35

        212-1112F

        Racing. Rear only. For FWD car with tendency for rear brake lockup.

        Project Mu D1 spec "F"

        .29-.34

        32-1022F

        Competition, drifting.

        Winmax W1

        .29-.32

        50-842F

        Street performance.

        Endless YZ080

        .28-.35
        /
        (also cited as .33-.38)

        572-1832F

        Endurance racing.

        Mintex F6R

        .28- (.40?)

        F

        Endurance Racing. Described as intended for low to medium torque situations to reduce rear brake lockup for FWD rear axle and RWD live axle rear axle.
        Manufacturer states it hits .40 somewhere?

        Project Mu D1 spec "R"

        .27-.32

        32-1022F

        Competition, drifting.

        Endless YS455

        .25-.34

        F

        Endurance racing.

        OEM

        .25-.38
        (~.30 for our example)

        F

        Dixcel Carbon Metal Series R16S

        .25-.30

        F

        Endurance. For Rear Axle.

        Endless NC44

        .22-.28

        32-1202F

        For rear axle of FWD cars to prevent rear brake lockup.




        Brake Pad Friction Coefficient Footnotes




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