Stop!!! Breaking News on Brakes

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November 30, 2010 | By: Scott Holton

We all love making our motorcycles go faster. Today, our topic is just the opposite——-Brakes. When we hit the brakes on our bikes, the force we apply to each master cylindergets transferred to each caliper via hydraulics. This applies friction to our brake rotors that the tires transmit to the ground, thus slowing us down. The point that we get the absolute maximum braking action is just before the wheel locks up. This seems kind of basic, but once that tire breaks traction our slowing action gets thrown out the window.

Let’s look at what actually stops us. As I mentioned above, the horse doing the heavy hauling is friction. When the brake gets applied we trade motion for heat. Initially, heat is our friend, but as the brakes heat up, we can’t trade as much heat into the slowing device and we start to get a condition known as brake fade. The first brake designs used expanding shoes inside a drum. The larger surface area of the shoes and drum made for excellent stopping power. However, the problem with a drum is getting it cooled enough before the next braking event. This is pretty hard to do. Drums are big, bulky, and retain a huge amount of heat. Ask any truck driver about coming down a mountain. He’ll educate you.

The next step for improving brakes was the advent of disc brakes. These did not apply quite as much leverage because of the smaller surface area, but the exposed rotors dissipated heat very rapidly. Disc brakes are used quite often today, with a little additional engineering though hydraulic force multiplication to apply the caliper pressure to the disc. The major advantage of a disc brake is its heat dissipation.

When discs brakes where used in road racing applications, brakes were pressed closer and closer to the fade point. After repeated use, heat would transfer to the hub melting the grease inside. This would lead to wheel bearing failure and in extreme cases, tire failure. To prevent this, floating rotors where developed. A floating rotor is retained by buttons to its carrier. This would transfer a fraction of the heat created to the hub, and recover from friction heat faster. This is the pinnacle of brake technology.

Ok, we have developed the brake as much as we can. What is the next step? Anti-lock Braking Systems (ABS). As we mentioned before, once that wheel begins to skid, all of our stopping efforts go out the door. An anti-lock brake system has a sensor at each wheel. When it feels the wheel stop turning, it releases the braking pressure to that wheel allowing it to turn again.

Honda, BMW, and now Harley Davidson have developed ABS. Optional on HD’s 2009 and 2010 FLT platform, they are now standard on 2011 Softails and Dressers.  How does this affect us? These new ABS braking systems require special bleeding processes. To get the ABS working properly, it must be hooked up to the computerized test equipment at your dealership to determine there is no air in the system. Maybe you think you’ve removed all the air, but it would be catastrophic if the ABS was activated and air was still present. This could result in serious injury or even death.  At this time, J&P is offering replacement lines, calipers and forward controls that are compatible with ABS. When using these components, a trip to your dealer is required. It is imperative that this be done. WE CAN’T STRESS THIS ENOUGH!!

As soon as more ABS components become available, we’ll get them added into our system.   Until next time, ride safe.

Comments: 2 Comments | Categorized Under: Tech Tips

Comments (2)

When you go faster you need to WHOA faster!!

Given the smaller contact patch offered by motorcycle tires compared to car tires, I’d say that any means of achieving better braking sound good to me…to a point. Linked brakes, while combining application of front and rear brakes into a single operation, take away from the ability to operate one set or another. Same for ABS systems. While they’ll perform wonders on the street (I’ve seen wet tests involving ABS vs. non-ABS for the same motorcycle), ABS will be an Achille’s heel on the dirt.

Ultimately, I’d say ABS would be fine, so long as it can be developed to the point that weight added is minimal.

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