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Hayes brakes
by chris churchill
created 7/30/2003
submitted 7/30/2003 03:25:30 PM

Principia's experience with mountain bike brakes

After using 3/16" steel discs with their corresponding heavy calipers, I was eager to use a more fitting system for our 2003 car. Looking at other cars in 2001, it seemed like mountain bike brakes could be the most efficient solution.
I chose some Hayes rear brakes because of their easy mounting and alignment. Unlike most of the brakes on the market, they mount to a flat plate and can be adjusted about 1/8" each way. Online, the calipers only cost about $60 each. They can be completely torn down, cleaned, and rebuilt in about half an hour each. The pistons are sealed by a rubber square seal that acts as a spring to retract the pistons slightly. More on that later.
Another advantage of the brakes is that their small size makes it possible to package the braking system almost completely within a NGM rim. Our suspension was very thin- just the rim plus a 1" kingpin. This will slim your fairings, decrease loads on your axle, and make your suspension lighter.
The first challenge was adapting the custom Hayes brake line to our 3/16" Nylaflow line. I finally figured out that you can attach the line directly to the caliper by using standard brass crimps with the included banjo fittings. It actually works quite well since the banjo fitting has a metal sleeve that fits inside the line, allowing the line to be bent considerably without any point stress.
During our Topeka qualifier, we found that even one pair of calipers gives enough braking power to stop a 600lb car, and two pairs makes it even easier.
I was very concerned about the stress of two calipers on a stainless steel disc that was only designed for one, so I designed a custom disc of the same thickness that had more spokes and was made of 01 tool steel. Unfortunately, this disc was a major problem with these brakes. Whenever the disc got too hot, with a long decelration on the freeway or a quick downhill stop sign, the disc would warp considerably. During ASC, before we found this problem, the discs warped almost a centimeter and had to be replaced. At each media stop, we would bend the discs straight by hand. As long as the driver was aware of the problem, we kept the warping down to an acceptable minimum, though our rolling resistance was still way more than it could have been. The discs were plenty strong enough; there was just uneven cooling that we couldn't predict or even track down. Seeing that other teams were able to accomplish safe braking with stock discs, I would recommend just buying a pair of 8" discs and doing enough testing to assure their safety.
Some people comment that hydraulic brakes are hard to bleed. These brakes were many times easier to bleed than our previous brakes. Our last brakes had 4 bleed valves and took hours to do correctly. The Hayes brakes only have one bleed valve, and with clear brake line, bubbles are pretty easy to get rid of. After several bleed sessions, we had the process down to about half an hour.
The hardest part about using these calipers, other than our warping problem, was alignment. The calipers only retract a hundredth of an inch, so there is very little margin for error. The alignment is more art than skill, and we were lucky enough to have someone that was good at it. Of course, our situation was hampered by discs that constantly changed shape. The alignment was also made difficult because of the close tolerances of our kingpin design. If you are very careful to align them carefully, you shouldn't have to do it again unless you remove the calipers.
The final issue people are concerned with is pad wear. Though we replaced our pads once during ASC, this was only because of our excessive scrub. On pads that didn't scrub as much, the wear was enough to get through all of ASC without replacement. Both pistons are floating, allowing them to come in as the pads wear. This feature also allows the pads to align themselves, to some degree, as the car drives. On several occations, our pads were aligned better after 50 miles of driving than when they started out.
The final mistake I made with this system is the selection of master cylinders. Our Airheart cylinders didn't have any negative pressure on the backstroke, making the calipers retract less than they could have. In addition, the bore on the cylinders was too great for our size, making the brakes a little sensitive. Other teams recommended motorcycle master cylinders, though I am a little wary of hand brakes.
If you avoid these mistakes, you should be able to implement a very light, compact, cheap, and efficient braking system on your car. If you have any questions, feel free to email me or use the yahoo listserv.

WSC addition:
For WSC 2003, we had new discs made from high temp stainless steel. After spending a lot of time aligning and straightening the new discs, we were able to get through all of WSC without any scrubbing or disc warping. The system worked flawlessly throughout. Another interesting sight: team Aurora also made their own discs for their bicycle brakes, and avoided warping by putting 8 radial slots, only 1mm wide, on the outside edge of their disc. The slots, they said, allowed for expansion and contraction of the outer edge of the disc without a tendancy to warp. Their discs are stilll good after 17,000km of driving!

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