Project Acura RSX Type S Brake Test - Tech

Day TwoWe were back out within a week to retest the new set-up. The lighter cloud layer and lower ambient temperatures meant surface temperatures this second day would be lower, making our tires slightly less greasy than during the previous test. There was also less wind, keeping dust off the track and reducing head- and tail-wind effects. We also (unwittingly) topped off the tank, so there was more weight in the back, contributing to more rear tire grip. Either way, results of each test should only be compared directly with other results from the same day.

To keep it fair, we started by testing the stock brakes under these conditions with the system freshly bled. We also noticed signs of possible flex on the stock front calipers from the week of street driving prior to this session. Even after the full test program, the transfer layer of pad material on the rotors had thinned radially, compared to when we just finished the first stock test.

Day two's stock 80-to-0mph braking distance averaged 211 feet, with a best of 201.2. The larger variation in this day's stock data means standard deviation had spread to 4.5 feet, still incredibly good. And again the pedal had gone soft, with pad smoke galore. Under full ABS intervention, Project RSX felt slightly more darty than on day one, indicating more rear bias-probably on account of the full tank. Stock results from day two were as we expected: a little better, considering the changes in conditions.

Following the same bleeding and bedding procedures, we installed the non-Type-S calipers and did the whole process again. Apparently, StopTech's engineers know what they're talking about, as stopping distances on most respective runs were as good, if not better, than stock. Average stopping distance dropped to 208.7 feet, which is still splitting hairs in our opinion, but at least it's a reduction of average braking distances of just over two feet. The best braking distance, however, was still a foot shy of stock. Pedal feel with the StopTech hardware was just as good as the first day and rotor temperatures exhibited the same trends.

The Secret To Stopping Five Feet ShorterWe're pretty happy that our premise of tires doing the braking still holds, as our data shows. In most other cases (outside of a highly refined sports chassis like the RSX), we'd expect a properly engineered kit to easily outperform stock brakes both in feel and consistency. In the case of hair-splitting on Project RSX, the secret was to further increase rear bias through proper piston sizing-the best way to adjust braking torque without changing pad friction characteristics, rotor sizes or compromising hydraulic pressure.

If we assumed that the A-Spec pads and the Axxis Ultimate pads have the same friction coefficient, then based strictly on the piston area and effect radius alone, we'd find the StopTech Type-S kit's front calipers have a force output which is four percent greater than stock. The non-Type-S calipers actually apply two percent less than stock. That's a six percent difference just by reducing two of the four pistons by 2mm in diameter.

For simplicity's sake, if we ignored the effects of different pad friction characteristics and assumed it was all the same, applied these calculations to some other front brake kits on the market based on the published piston sizes and rotor diameters, then we get an idea of where other brands might stand relative to stock in terms of front caliper force output.

One brand goes much higher, while the other is even lower than the StopTech non-Type-S kit. Although the change in force output/braking torque in front doesn't necessarily dictate overall brake bias (since some manufacturers don't indicate which pads are used in the rear), it does give a reference for how to set up a braking system.

And just because it worked on our RSX Type-S doesn't necessarily mean you should do it too. Our car has been seriously tweaked: significant weight reduction, lowered center of gravity and a much stiffer suspension; all things a brake kit manufacturer can't account for.

In the real world, brake engineering and balance isn't just about how fast you can stop. Brake engineers and OEMs know this, and it's the last piece of the puzzle we didn't get to test between the three set-ups. Often ignored in the aftermarket, braking stability in a turning/braking situation plays a critical role.

The Society of Automotive Engineers (SAE) has a set procedure and protocol for this. Essentially, the test measures how a car behaves and where it ends up when the brakes are fully applied when circling a skidpad at its limits. A car with more rear bias will rotate and end up well inside the original line of travel, while a car with too much front bias will push well outside the skidpad. Maintaining a balance that allows the driver to keep going where the front wheels are pointing is critical and is also one of the factors behind StopTech using less-than-optimal rear bias in order to keep the car on line.

For Project RSX, we prefer the added feel and margin of safety offered by the StopTech kit. If three feet of braking is outside the margin of your tires and control, you're probably overdriving.