Brakes are the most essential system in your race car. The consequences of being unable to stop can take a fun day at the track and turn it expensive or even deadly in the blink of an eye. In this article, I will explore the basics of how disc brakes work. I’ll use my time attack/wheel-to-wheel BMW E90 as an example of how you can use fundamentals to make your braking system worthy of competition abuse. Warning: this will be nerd-heavy, so save it as a bookmark. Kinetic Energy Into Thermal Energy When you step on the brake pedal of your average road car, the force your leg produces is multiplied by 6:1 to 7:1 for brake systems without a brake booster and 4.5:1 to 5:1 for systems with a booster. That force is then changed into a hydraulic pressure via the master cylinder. The hydraulic pressure reaches the brake calipers at the wheels through a series of hard and soft lines. The hard lines are typically made of steel and/or stainless steel. The hard lines connect to soft lines, which are made out of rubber or a combination of rubber, synthetic materials, and stainless steel. This allows for articulation, as the calipers are attached to the suspension, so the freedom to move up, down, in, and out is necessary. That force pushes a piston, or pistons, inside the caliper onto a brake pad made of friction material to clamp the brake rotor. The rotors are attached to the wheel via wheel studs; thus, this is how the car slows down. The brake pads convert a vehicle's kinetic (motion) energy to thermal (heat) energy through friction on the rotor. This heat is dissipated into the surrounding air through convection (heat transfer between masses at different temperatures). Generally, the front brakes absorb 70% of the vehicle's kinetic energy, and the rear brakes absorb the remainder. The front brake rotors are typically oversized and vented better than the rear. Now that we know the basics, we can work on improvement. If you have drum brakes, I advise you to change them to disc brakes for better thermal management. Line Em' Up, Brake Hoses The first modification you should make is ensuring you have PTFE (polytetrafluoroethylene) brake hoses (often called brake lines), usually wrapped in stainless steel. Be sure to purchase from a company registered with the United States Department of Transportation (more on that later). I recently had a revelation: rubber brake hoses are a wear item. The Department of Transportation (DOT) regulates all brake hoses on cars sold in the United States. They must conform to the FMVSS 106 and SAE J1401 tests. One specification that an average brake hose assembly must achieve is the ability to withstand pressure of 4,000 psi for two minutes without rupture. They also must pass the whip test, which continuously bends soft lines on a flexing machine for 35 hours at pressure. The last big one would be the slow pull and fast pull tensile test. In the slow test, the hose must withstand a pull force of 325 lbs without separating from its end fittings. During the fast pull test, that 325 lbs is upped to 370 lbs with the same stipulations of not separating from its end fittings. To have a brake hose on an OEM car in North America, they also have specific markings, and must meet temperature resistance, ozone resistance (for cracking), and corrosion resistance standards. I know what you are thinking, "Then why the hell am I replacing the ones that came on the car, Devin?" Well, sit back down, junior. Your brake hoses live in a harsh environment. They are peppered with salt, dirt, and brake dust, among other things. These all cause corrosion on fittings. Then, there are multiple heat cycles with dramatic cooling. I could go on and on! Brake lines don't get the inspections they deserve and are often forgotten if they are working and have no signs of leakage. You should inspect your brake hoses for blisters or bubbles. If you rapidly push down on the brake pedal and see the hose deform, replace them. You should also look for cracks by trying to flex the hose. If there are any, replace the hose. Check the brackets that hold the brake hoses to a suspension components. If they are damaged or rusty, they may pinch the hose, meaning you should replace them. Fittings are plated to prevent corrosion. If this plating wears off, it can accelerate wear. Brake hoses also tend to swell with age, which causes restricted flow. Brake hoses can also deteriorate from the inside with no warning signs. Moisture in brake fluid (brake fluid is hygroscopic and absorbs moisture from the air) also damages the reinforced fabrics. Lastly, you should run your finger along the length of the hose, and if there are any irregularities, you fucking guessed it, replace the hose. DOT Compliant You want to ensure you get your hoses from a company registered with the United States DOT to sell brake hoses. This means their products have been tested to the above standards and passed. I see this often in the grassroots motorsports world where a consumer assumes that when it says "stainless steel lines," they are all the same. It's certainly possible to buy a worse product than your OEM rubber hoses. A few quality companies that come to mind are Stoptech and Goodridge. Stoptech, which is owned by Centric, is an OEM level manufacturer. Their aftermarket lines are pressure tested to 4,500 psi instead of the 4,000 psi minimum. Goodridge is another company that takes things a step further and tests their hoses at 12,750-13,500 psi. Goodridge also manufactures for OEMs as well. Both of these companies adhere to FMVSS 106 and SAE J1401 tests. Many older cars you see on the track could benefit from new lines. I noticed the hoses on the E90 were cracking and had clear signs of corrosion on the fittings, … Continue reading Nerd Talk: Brakes Part 1
