How Brake Systems Work - CHP How It Works

Industry Brake Experts Explain Rotor Design, Mega Piston Calipers, Pad Compounds, And Brake Alloys

Stephen Kim Jul 27, 2010 0 Comment(s)
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Rotor Diameter
Todd Gartshore: "Larger rotors do in fact improve braking performance due to the extra leverage they offer. This concept can be illustrated with your own toolbox. Try loosening the head bolts on your next project with a short-handled ratchet, and after turning yourself red from exertion, place the socket on your breaker bar. That's not too different with what happens with a larger diameter rotor. As the distance from the center to the perimeter of the rotor is increased, leverage is increased as well. The torque improvement of a larger rotor diameter can be individually calculated based on the before and after rotor sizes. Without changing the friction compound, increasing a rotor's diameter is the only way to improve brake torque and shorten stopping distances unless other areas of the brake system are changed."

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Carl Bush: "Rotor diameter has a measurable influence on stopping power due to the leverage it provides to the caliper in order to stop the wheels. The leverage that a caliper has is based on the distance from the axle or spindle centerline to the center radius of the brake pad contact face. The amount that radial distance to the pad centerline is changed, by moving the caliper outward on a larger diameter rotor, is directly proportional to the increase in stopping power. For example, if you increase that distance by 10 percent, you increase leverage by 10 percent as well."

Michael Jonas: "Maximum rotor size is ultimately determined by wheel diameter and wheel spoke design. That said, a larger diameter rotor generates more stopping leverage than a smaller rotor. The gains in performance won't be that great when stepping up from a 13- to a 14-inch rotor because it's only 1/2-inch bigger on each side. However, there will be a substantial increase in stopping power when stepping up from an 11- to a 13-inch rotor. Cars with larger diameter rotors will require less pedal effort. The nice thing is that you don't always need a bigger caliper when upgrading to a bigger rotor. At SSBC, we now offer big rotor kits that relocate the stock calipers farther outward."

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Two-Piece Rotors
Todd Gartshore: "Two-piece rotors use a separate hat assembly that bolts to the rotor itself. By using a rotor with a separate hat, the overall rotor weight can be dramatically reduced. For example, a Baer EradiSpeed two-piece rotor for a C5 Corvette is 3.8 pounds lighter than the stock rotor. This particular example is not a direct comparison since the EradiSpeed design has more mass around the outer plates than the OE rotor, thus adding heat absorption improvements directly in the fire path of the rotor. Another benefit of a two-piece rotor design is longer hub life resulting from less thermal transfer from the rotor into the hat. In the hot rod market, the most compelling reason for two-piece rotors beyond weight is that they give you the flexibility to vary offset very easily for easy fitment behind different wheel designs."

Carl Bush: "In most two-piece rotor assemblies, the bolt-on iron rotors are attached to an aluminum hat, rotor mount plate, or sometimes directly to the aluminum hub. Two-piece assemblies offer several advantages, but one of the biggest reasons from a performance point of view is that more iron can be concentrated in the pad wear faces and cooling vanes while at the same time reducing unnecessary rotating and unsprung weight by mounting the rotor to an aluminum hat instead of using a single piece of iron or steel. Once again, the goal is to maximize cooling and durability, while eliminating unnecessary weight that does not contribute to cooling."

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Brad Burleson: "Two-piece rotors allow you to reduce weight by making the hub out of a lightweight material like aluminum, but still leave plenty of mass in the rotor for effective cooling. Aluminum also dissipates heat faster, keeping the system cooler. They do cost more initially, but later on it is cheaper to replace just the rotor instead of the whole assembly. One of the biggest benefits is that they resist warping due to overheating much better than one-piece rotors."

Todd Gartshore: "All Baer calipers are built from aluminum. Although most are made from a 6061 alloy, a 2618 alloy is used in Baer's Forged MonoBlock units. This is the same alloy often used for pistons in race engines. The benefit of 2618 is that it's a very stable material at sustained high temperatures. Baer employs this alloy along with MonoBlock technology in both its 6S and 6R calipers. Due to cost versus performance concerns, we believe iron is still the best available choice of material for rotors."

1009chp_08_z How_brake_systems_works Rotor 5/13

Carl Bush: "Most brake rotors are made from one type of cast iron or another. OE brake calipers are generally cast iron, aluminum, or some combination of both. Aftermarket street performance and race calipers are usually aluminum, but there are also other high-tech exotic alloys that can be used for extreme special-purpose parts. In racing, you can find rotors made from a number of materials including iron, steel, stainless steel, titanium, aluminum, and a whole range of carbons and ceramics. The application of rotor materials isn't a subject to approach without a full understanding of the material and purpose. An aluminum rotor can perform flawlessly on a lightweight open-wheeled sprint car racing on a high-momentum dirt track. However, that same rotor would melt down in a heartbeat on a street car and set the stage for a potential catastrophic failure."

Michael Jonas: "Rotors are typically built from cast iron with various levels of carbon added to them for strength. Some race cars and high-end street cars use carbon rotors that are very light and generate little heat. The downside is that they're extremely expensive and very brittle. It's possible to break a carbon rotor by over-tightening the lug nuts. As far as calipers are concerned, older cars used cast iron with steel pistons. Aluminum calipers are 4 to 12 pounds lighter than a comparable iron caliper, and that reduces unsprung weight and improves ride quality. The pistons inside the calipers are made from aluminum or steel, but lighter aluminum pistons aren't necessarily better. We offer aluminum and iron pistons, but prefer using stainless pistons because they don't transfer as much heat, and also dissipate heat more effectively."


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