Since I'm trying to figure out an appropriate brake upgrade for my 1988 Mazda 323 GTX, I read your article ('Point Brake', Oct. 2007) on the RSX brake kit with interest. But I came away confused. You ask at the beginning of the article: "How do big brake companies go about claiming improved braking performance without changing tires? The answer: braking balance." Later, at the top of page 116, you expound on this: "Most cars off the showroom floor have a front-biased brake system..."
You also mention that the RSX (or maybe just the Type-S, it's not clear) is unusual in that Acura created a true driver's car, with balanced braking, and that's at least partly why StopTech's kit did nothing for stopping distance.
But why did Acura go to larger front brakes on the Type-S, if most cars are already front-biased? And why is StopTech-and almost all aftermarket brake kit manufacturers-creating larger front brakes when most cars already have too much front brake bias? I would expect most kits to have larger rear brakes. StopTech may have been 'fooled' with the RSX because it already had balanced brake bias, but even if it didn't, even if it was like most production cars and had a forward brake bias, that would just make StopTech's kit even more confusing.
Bottom line, I don't see how this article explains how aftermarket brake kits shorten stopping distances or improve brake balance on anything but a car that has too much rear brake bias. Any clarification would be appreciated.
Jim Chittenden
Highland, NY
I had to rethink this a couple of times before realizing why (although you're on the right track) you've completely missed the point of what we've been trying to explain about brakes, upgrades and our meticulous testing.
Just so everyone else is on the same page, let's recap. In the final installment of Project Acura RSX Type-S, we stopped procrastinating and set out to test the StopTech brake upgrade kit we've had on the vehicle since day one. The test is our standard procedure for back-to-back comparison of a car's stock brakes and an aftermarket brake upgrade kit. 80-to-0mph braking distances, as well as front and rear rotor temperatures, were recorded for every other run through a total of 20 runs. Then we spent an afternoon on the asphalt, swapping the hot brakes and running the test all over again-with the stock hardware, on the same tires, under the same conditions. Assuming the kit was designed with near-neutral brake bias in mind, we anticipated better (if not the same) braking distances than stock Type-S brakes could provide.
While pedal feel and rotor temps were improved drastically over the stock hardware, actual braking distances fell a hair shy. Hair or mile, we figured people would overlook the main advantages of a high-performance brake kit and get stuck on the idea of paying money for longer braking distances. So, scratching our heads, we consulted StopTech's engineers who ventured a possible solution using their non-Type-S front calipers for slightly less front bias. We repeated the test. To explain why we were able to match and just beat the already good stock braking distances (slightly), we got into explaining brake bias (or balance) and how to figure it out with brake torque equations.
While you seem to grasp the concept of optimal braking through balanced front and rear bias, here's the point of big brakes: bigger brakes cope with heat better. That's why track-bound cars insist on larger rotors and calipers, as well as race-compound brake pads. Larger rotors have more thermal mass, so they can take a lot more brake energy before transferring heat to the pads and fluid, which results in fade.
Larger brake rotors also dissipate more heat because of the increased surface area for irradiative and convective cooling, as well as the larger radius, which is more effective at forcing convecting air through the vanes. Most of the time, high-performance rotors also have better vane designs and thicker profiles.
Obviously, everyone upgrades the front brakes first since the front brakes do the majority of the braking under weight transfer, which means they suck up a lot more heat than the back. Big brakes on track cars are about dealing with heat to maintain consistent braking lap after lap, which is so strenuous that our 20-cycle braking test doesn't even come close
Then some car-show yahoos got the idea that if race cars have big brakes, then they too must have big brakes. And because show kids don't know any better, they install the largest random rotor and caliper combination they can stuff inside the front wheels and leave the rear drums in (spray-painted to match, at best).
Increasing rear bias proportionately through a larger effective radius, piston area, friction coefficient, or even line pressure, never occurred to anyone who wasn't a brake engineer. And there was nothing they could do to convince customers to invest just as much into upgrading the rear brakes properly to match the increase in front bias.
In the case of our Project RSX, we did just that with both a big brake upgrade in front and with proper pad selection in the rear. The reason it underperformed against the stock car, contrary to StopTech's original research and development, was because our car was significantly lower, had stiffer spring rates, and different weight distribution than a stock, full-interior car on sport springs. Ours was gutted in the rear, had turbo hardware in the front and was on coilovers that took out almost all body motion, greatly affecting weight transfer-a critical aspect when figuring out the proportion of front-to-rear braking grip.
Even with the off-the-shelf, larger-piston, front-biased RSX Type-S calipers, our RSX missed the mark by just a few feet. With the subsequent installation of the smaller-piston, non-Type-S calipers, we were able to balance the brake bias to match or better the stock braking numbers, but probably at the cost of braking stability during turning.
And just because the Type-S uses larger front rotors than the non-Type-S model doesn't necessarily mean it has more front brake bias. Maybe the front pistons are smaller, or the rear pistons are increased in size. Even changes in front-to-rear spring rate or damping ratio affect weight transfer and thus bias.
Ultimately, I think most people miss the point of brake upgrades. While we evaluate stopping distances, which are easy to quantify and illustrate where improvements are made, it really is a matter of chasing a number that has little impact on real-world driving on the street. How often have you actually had to make an emergency stop from 80mph? Brake pedal feel, heat dissipation and resilience are what really matter in a fast car
While you seem to grasp the concept of optimal braking through balanced front and rear bias, here's the point of big brakes: bigger brakes cope with heat better.