Brakes are among the most important components of your bike, and not just for safety. It’s obvious that being able to stop quickly can be important for safety, so you need brakes that offer excellent power. For the enjoyment of cycling, the brakes’ modulation is just as important. The last thing you want is a brake that suddenly “grabs” the rim, when you brake deep into a corner to increase the traction on your front wheel as you turn in.
Brake flex is the enemy of good braking performance. When your brake flexes, your hand power on the lever no longer is translated into braking power at the rim. Many brakes feel great at first, but as you squeeze the lever harder, brake power no longer increases, because the brake just flexes.
Flex is rarely a problem on racing brakes. They can be small and stiff, since they only have to wrap around a narrow tire. When sidepull or dual pivot brakes are enlarged to reach over wider tires and fenders, they rarely offer great performance. Large brakes are simply too flexible.
The solution is to shorten the brake arms by attaching them closer to the rims. Cantilever brakes use pivots that are attached to the fork blades and seatstays, close to the rim. This keeps the arms short and makes the brakes very powerful. However, cantilever brakes tend to twist the fork blades and stays as they are applied, which changes the angle (toe in) of the brake pads: The brake then suddenly grabs the rim.
A better solution is to attach the pivots higher, near the fork crown (front) and seatstay bridge (rear), where flex is not an issue. Centerpull brakes do this, and their lower arms are short and stiff. Their upper arms only transmit the linear forces from the brake cable to the pivot, so they can be slim and yet don’t flex much.
Not all centerpull brakes are created equal. The lever ratio between upper and lower arms must be carefully chosen to offer good braking power, and the brake arms themselves should be optimized for light weight and stiffness.
What about disc brakes? They can offer very good performance, but they are heavy and require stiff forks, because the braking forces occur near the hub instead of at the rim. A stiff fork does not absorb shocks well, so it is an inferior choice for a bicycle that is ridden on all types of roads.
The idea that centerpull brakes offer the best performance is becoming more and more accepted even by mainstream makers. Whether it’s the superlight eebrakes or Shimano’s latest road models, the best brakes today place the pivot next to the tire just like centerpulls do. Their actuation is more complex and heavier than classic centerpulls (to eliminate the need for a cable hanger), but the basic principle is the same. It simply makes too much sense, and everything else seems like a compromise.
The Compass centerpull brake uses the best pivot location, ideal lever ratios, and a shape optimized by Finite Element Analysis, to provide the ultimate in brake power and modulation that a rim brake can offer.
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