Tires stop a car, not brakes. Even if that's a broad statement, full of caveats and qualifiers, it contains a crucial truth. All things being equal, stopping distance is stipulated by how much grip the tires have before they're finally overcome by braking torque, resulting in wheel lock. For those with ABS, the surest and simplest way to reduce dead-stop braking distance is a simple matter of stickier tires.
So how do big brake companies go about claiming improved braking performance without changing tires? The answer: braking balance. And that's the reason why we devoted two whole days to comprehensive brake testing, one of which was completely unanticipated.
As you might have seen from various Project RSX pictures, a set of StopTech brakes were already installed when we inherited the car. It's a complete set-up, engineered to optimize braking performance through better front-to-rear balance. The kit consists of stainless steel braided brake lines, 328x28mm (12.9x1.1-inch) slotted two-piece, fully floating rotors with aluminum hats for the front, four-piston fixed squeeze-forged aluminum calipers with StopTech's patented X-brace bridge design, Axxis Ultimate pads for the larger front and stock rear calipers, and all the necessary hardware and brackets to mount the larger front brakes. We never mentioned them before because we hadn't got around to doing a full brake test involving A/B comparisons with the stock hardware. Now that the completed Project RSX is ready for its final performance figures, it was the perfect time to break out the testing gear.
Our comprehensive brake test program involves 10 repeated 80-to-0mph runs, measuring rotor temperatures on each run as well as the total braking distance. The first measurement is performed with rotor temps at near-ambient prior to the run, so we have a more complete picture of stopping performance over a broad temperature range. And since modern brakes are so damn good at stopping in spite of high temperatures, we also do an 80-to-0mph run on the unmeasured outbound trip, in order to keep brake temps up and try to get stock systems to fade.
Brake testing can be a lonely gig.
Day One
We took Project RSX out to the track with the StopTechs already installed, pads properly bedded and the system pre-bled with fresh Motul RBF600 brake fluid. Conditions would be more or less ideal: using the same track on the same day on the same relatively fresh Hankook Ventus Z212 maximum-grip tires. Having conducted this test countless times, we have a decent idea of what constitutes a good braking distance for a car of this weight and how much variation to look for as the brakes heat up. Project RSX averaged an 80-to-0mph braking distance of 219.8 feet (disregarding the first cold stop) with a best of 213.3 feet. We expected nothing less.
For you statistics nerds, that amounts to a standard deviation of (or 68 percent of all stops falling within) 5.1 feet from the average braking distance. This is almost nothing compared to the variations we see in most ABS-equipped cars with modified brake components. Front and rear rotor temperatures were within 160 degrees F of each other, even with the dust shields installed.
After a quick lunch to let the rotors cool, we took off the StopTech kit and installed stock RSX Type-S front rotors and calipers, using Acura's A-spec pads. We left the braided lines on to keep things fair and re-bled the whole system. With the new pads properly bedded and heat-cycled with an evenly distributed transfer layer of the new pad material on the rotors, we repeated the test.
We expected to see much higher front rotor temperatures, a squishier pedal feel and maybe even some brakes on fire at the end of the runs. With any luck, the stopping distances would be just a little longer than the numbers collected earlier with the StopTech system, but not so different as to throw out our grandiose claim of tires making the most difference.
On its stock brakes, the car did everything we expected, but also posted a shorter braking distance on almost every corresponding brake run. On average, the stock brakes stopped the car in 216.1 feet, 3.7 feet shorter than the StopTech average. It also posted its best distance of 210.6 feet on the fifth run, even with the pedal going soft and the pads billowing smoke.
Obviously, these numbers were going to piss on StopTech's parade and ours. Even though the big brakes were far superior in terms of rotor temperatures, pedal feel and modulation, the longer-than-stock stopping distances would undoubtedly raise some questions as to the validity of spending several thousand dollars on an upgrade. And even though we'd prefer some semblance of pedal feel on the track with the big brakes over a negligible difference of less than four feet (remember this is still within one standard deviation of the data collected), it's still a little embarrassing.
We consulted with StopTech's engineers and sent them our data, so they could defend their product before we blasted them with our published automotive blasphemy. They agreed our testing methodology was decent enough for a bunch of magazine weenies and that the longer braking distances were probably on account of the modifications made to Project RSX, and possibly slight changes to the ABS calibration and braking hardware on the newer 2005 RSX Type-S. StopTech had performed extensive testing of its Type-S kit on a then-new 2002 model with springs and street tires, and was able to obtain favorable braking performance in every parameter. Our car far exceeds the capabilities of StopTech's test vehicle.