Brake Performance - CHP Insider
Brake Performance - CHP Insider
http://images.chevyhiperformance.com...rformance+.jpgUnless you've had a run-in with a sand trap or tire barrier, you probably pay as much attention to your brakes as a soccer mom does to her oil-change regimen. What you may not realize is that your brakes perform what is arguably the most important function of any automotive device. Sure-that's, like, way clich-but this is one situation where you want to avoid learning through firsthand experience, because doing so will probably hurt. Moreover, upgrading your brakes isn't just for road racers. Every horsepower you add is another reason to improve your car's stopping ability. For more than three decades, Stainless Steel Brakes Corporation has been offering enthusiasts cost-effective brake upgrades for musclecars, street rods, and late-models. The company's products include a full line of disc-brake conversions, big brake kits, pads, rotors, and other assorted brake goodies.
The apathy of the general public means fact and fiction are difficult to distinguish from each other when it comes to performance brakes. For instance, will that extra inch of rotor diameter really make a difference? Is there a point of diminishing returns when it comes to the number of pistons in a caliper? Does cross-drilling really help dissipate heat? Fortunately, thanks to SSBC President Michael Jonas, we have answers to the most common questions and insight into some more-controversial topics.
Drilling And Slotting
Cross-drilled and slotted rotors look tough, but do they offer any performance benefits? Yes and no. "Rotors are cross-drilled because it looks cool," explains Michael. "The main problem is that most rotors are made in China right now, and with their lack of strength, the cheaper rotors that are drilled will crack, guaranteed. That's a severe issue, since cracks can lead to pieces of a rotor eventually breaking off." On the other hand, slotting does not change the structural integrity of a rotor and affords genuine performance advantages. "A slot done correctly results in a continuous sweep across the pads, which cleans them more effectively and improves wet-weather braking. As pads stay cleaner, they last longer."
Weight Transfer
The reason mid- and rear-engine cars stop so well is their lack of excessive weight transfer under braking. Since it's not practical to relocate the engine in your musclecar's chassis, proper suspension setup is imperative. "Just as with piecing together an engine combination, braking is a system that includes the suspension, wheels, and tires in addition to the actual brake hardware," says Michael. "In terms of suspension setup, run stiffer springs up front and softer springs in the rear to prevent excessive nosedive and keep more weight over the rear wheels. The reason full-frame cars brake so much better than unibody cars is that they don't unload the rear tires as much. With a unibody car, installing subframe connectors can significantly improve braking."
Wheel Size
Wheel size and design have major effects on braking performance and brake fitment. Larger wheels carry greater rotating mass, which reduces braking ability. Hence, bigger rotors and calipers are more of a necessity than a luxury when increasing wheel diameter. In addition to size, wheel design dictates the brake package size. "The last thing you want to do is spend a bunch of money on wheels and tires then realize the brakes you want to install won't fit, so select wheels and brakes together as a package" says Michael. "Large wheel lips reduce the available space for brakes, as can the design of the spokes, so you must take thorough measurements to ensure proper fitment. Determine brake clearance by measuring from the flat spot of the wheel behind the lug-nut holes to the back of the spokes."
Traction And Braking
Everyone's stuck on rotor diameter and caliper piston count, but the importance of tire grip is often overlooked. To prevent excessive lockup, tire traction plays a significant role in overall braking performance. "Adding a big brake kit without upgrading your wheels and tires is like having a big-block car running on bias-plies," Michael quips. "You can't get braking force to the ground with small tires, and it's important to have a sticky compound as well. Having an adequate amount of contact patch is critical, so don't expect a car to stop well with skinnies or cheap tires."
Rotor Diameter
Massive rotors are a hallmark of big brake kits, but how do they factor into the total braking equation? "Larger rotors don't necessarily increase bite over smaller rotors, but like using a longer connecting rod in an engine, they do increase leverage," explains Michael. Additionally, with larger rotors comes greater heat capacity, which helps reduce brake fade. "In essence, rotors are heat sinks. Since larger rotors are usually thicker than smaller rotors, that additional mass prevents heat from transferring into the calipers and fluid."
Floating vs. Fixed Calipers
"In a floating caliper design-which is most commonly used by the OEs-the pistons are only placed on the inboard side of the rotor, and the caliper slides on pins to exert force on the outboard side of the rotor. On the other hand, since a fixed caliper has pistons on both sides of the rotor, the caliper itself does not need to move, just the pistons. A floating caliper is less expensive and will fit more wheels because the design is more compact. They're often a better option in applications with low-end wheels that don't have adequate brake clearance since they fit just about anything. That's why we created a three-piston sliding caliper. The advantage of a fixed caliper is that it exerts equal pressure on both sides of the rotor. Floating calipers tend to have uneven pad wear, since they exert more pressure on inboard side. Also, if the sliding pins aren't maintained, you'll get uneven brake pressure. Generally, fixed calipers are preferred in heavy-duty performance and racing applications."
Cryogenic Treating
Hop on any online road racing forum and you'll come across some banter over cryogenically treating brake rotors. So what is it and do you need it? The process involves repeatedly chilling a rotor in liquid nitrogen then letting it warm backup to room temperature. "Cryogenics realigns the metal structure by squeezing it all together, which makes the rotor stronger," says Michael. "It makes a rotor last longer, but not that much longer. Since it's very expensive, there is some benefit of cryogenics for track use, but it's not worth it for the street."
Piston Count
"Clamping force is based on surface area, so you want as much piston coverage behind a pad as possible. However, you must achieve a good balance of the number of pistons and piston diameter. More pistons give you more clamping force. For instance, a factory C5 Corvette caliper has two small pistons. Our Tri Power caliper is based on the C5 design, but by simply adding a third piston we've been able to increase clamping force by 50 percent. However, regardless of piston count, pistons that are too small will give you a hard pedal. Just as an engine with small pistons won't make much power, the same situation applies to braking. Four large pistons are usually better than six small ones. Even I didn't believe that until I sat down and calculated it."
Pads
Selecting the right brake pads for your application is just as important as selecting the proper tires. Camshafts are designed to work in a specific rpm range, and similarly, brake compounds are designed to work in a specific heat range. No one pad can cover all heat ranges. "Using a full-race-type pad on a street car is just as dangerous as using OE-type organic pads on a race car," says Michael. "Factors in selecting a brake pad include vehicle weight, brake temperature, and how the vehicle will be used. Entry-level pads are organic, and semimetallic pads are a good upgrade for the street."
Break-In
Fresh brake pads require some sort of break-in procedure, and while this should be common sense, follow the manufacturer's instructions to make sure you don't ruin your new pads. "Different pad compounds need to be broken in differently, so it's very important to obtain the manufacturer's specific procedure instead of relying on info from some random source," explains Michael. "Some manufacturers suggest stomping on the pedal two or three times from freeway speeds, while others recommend several slow stops from 30 mph."
Brake Fade
"When a rotor can't absorb any more heat, the excess gets transferred to the brake fluid, which is what gives you brake fade. When this happens, the brakes are developing heat faster than it can be dissipated. The most obvious solution is learning how to get around the track without relying on your brakes as much. If you've done that and are still getting fade, high-temperature brake fluid and high-performance pads are your next step. Stainless steel pistons have less heat transfer and dissipate heat faster than aluminum, and larger rotors increase heat capacity as well. One thing that is often overlooked is the design of the wheels. Open-face wheels make a huge difference in braking over wheels with more of a closed-face design. When we track-tested a closed-face '89 Corvette wheel and a open-face ZR1 wheel back to back, there was a 75-degree difference in brake temperature."
One- vs. Two-Piece Rotors
Most OE-type rotors feature one-piece construction, while some high-end rotors are two-piece designs, in which the rotor and hat are separate units attached by bolts. One of the advertised advantages of a two-piece rotor is reduced unsprung weight, since its hat is aluminum. However, not everyone agrees. "For street applications, a two-piece rotor only reduces weight by 1 pound," explains Michael. "Why would you reduce weight when it comes at the expense of reduced heat capacity? If you want to reduce unsprung weight, there are better ways to do it, such as with lighter wheels or calipers." According to Michael, the primary benefit of two-piece rotors is their flexibility in design, allowing them to fit a wide range of wheel offsets. "The nice thing about two-piece rotors is that you can move the hat in and out where you want it in relation to the wheel, but more pieces increase the chances of something breaking."
Rear Discs
If the front brakes do most of the work, is it really worth it to upgrade your rear drums to discs? You bet. "A car with rear discs will always stop better than a car with rear drums," says Michael. "Not only are they more efficient, rear discs will improve stopping distance by 25 to 35 percent. In a car with front discs and rear drums, the brake shoes last two to three times longer than the front pads, which should really tell you something about how much work they're doing."
Manual vs. Power Brakes
Not only were power brakes a rare commodity on musclecars, chances are your engine has too much cam to generate enough vacuum to run a booster. That being the case, going through the effort of installing power brakes only makes sense if it significantly improves braking performance. According to Michael, the only real advantage of power brakes is reduced pedal effort. "Manual brakes develop about 1,200 psi of line pressure versus 1,500 psi for power brakes," explains Michael. "Although higher line pressure can slightly improve braking performance, the difference between the two is marginal at best. Power brakes mean you don't have to press the pedal as hard, but that's their only benefit."
Bleeding Lines
"This is going to come as a surprise to most people because it sounds so simple, but the best way to purge the air out of your brake system is to gravity-bleed the lines. This means no vacuum pumps or stepping on the brake pedal. To gravity-bleed, simply put fresh fluid in the master cylinder, open the bleeder screws, and let gravity remove air from the system. When the fluid starts pouring out, you're done. You can do all four brakes at same time or one at a time. Since it's a one-man job, the entire process takes just 20 minutes. Of course, you must bench-bleed the master cylinder first."
Photo Gallery: Brake Performance - CHP Insider - Chevy High Performance Magazine
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