Brake Upgrade - Stop It!

Caliper Clamping
A bigger rotor by itself isn't going to have much of an effect on stopping power. You need to combine that big disc with a caliper that has enough clamping force to haul it down. But do you really need a caliper with six, or even eight, pistons to get the job done?

"You have to match your brake force to your car's horsepower," said Dominic Chen. "Too much force can lock up the wheels and upset brake balance. If you have a brake kit that's too big or weighs a lot, you're not getting the bang for the buck in terms of performance."

"Keep in mind," added Bush, "that the piston volumes within the caliper must remain matched to the volume capacity output of the master cylinder." Translation: If you've gone really big with rotors and calipers, your stock master cylinder may not be pumping enough juice for the pistons in the caliper to achieve their maximum clamping force. You may need a master cylinder upgrade, matched with a brake booster to maintain the level of pedal effort you had prior to the upgrade.

While we're on the subject of fluid, two things: First, there's a reason brake upgrades often include braided-steel brake lines, and it's not just for cosmetic reasons. The rubber hose between your car's stock hard lines and the caliper can swell due to age or because of increased fluid pressure in the lines. That swelling increases pedal travel and makes it feel all soft and spongy. The current generation of high-performance brake lines offers a steel-braided outer cover with a Teflon inner liner, both of which prevent brake line swelling.

Second, not all brake fluids are created equal. Like brake pads, they have operating temperature ranges; in this case, they're classified by their boiling points. These correspond to government labels-the DOT 3, DOT 4, and so on-you find on brake fluid containers. The higher the DOT number, the higher the fluid's boiling point. Why does this matter? Brakes can get hot enough to boil the fluid, particularly if the fluid has absorbed some water over time, which lowers its boiling point; or if you're using a street-oriented fluid under competition conditions. Fluid boiling creates gas bubbles in the brake lines, which result in a soft or spongy pedal.

Upgrading to a higher DOT rating pushes the fluid's boiling point beyond the risk of boiling during hard use. The highest rated fluid you can use, with a DOT 5.1 rating, has a dry boiling point of 509 degrees F, compared to 446 degrees for DOT 4 and 401 for DOT 3. Unfortunately, DOT 5.1 fluids also have retail prices that are several times higher than DOT 4 fluids. Don't confuse a DOT 5.1 fluid with a DOT 5. They have the same dry boiling point, but DOT 5 fluids are silicone based, while DOT 5.1 (as well as DOT 3 and 4) fluids are glycol based. A degree in chemistry would help you sort out the differences; suffice it to say that the silicone-based fluids are more compressible than the glycol-based ones, meaning they'll give you the same spongy pedal feel that glycol fluids exhibit only after boiling.

How often should you change your brake fluid? According to Stillen's Chris Bernal, you shouldn't go longer than two years between flushes "if you're on the street. On the track, probably after every event."

A Matter of Balance
As you look at other modified cars around you, you may notice that some have massive brake upgrades on the front wheels but little, if anything, done to the rears. That can mean that the car builder ran out of money, but it can also indicate a smart buildup plan.

Why? In most cases, a car's front wheels do something on the order of 80 to 85 percent of the braking, largely because of the weight transfer over the front wheels that occurs during deceleration. In a lightweight, front-wheel-drive car, the fronts can do 90 percent, or more, of the braking. That being the case, it makes sense to upgrade the end of the car that's doing the most work. Or, as many of our experts recommended, limit the rear end upgrade to maybe rotors and pads only, to maintain the car's proper brake balance.

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