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Most new motorcycles seem to come with two disc brakes in the front. My bike only has one disc brake in the front and I can easily brake hard enough to make it activate the ABS, thus making my front wheel oscillate between blocking and rolling. If the front wheel is blocking with one brake already, what is the benefit of adding a second brake to it?

Obviously one would need to replace the brake pads and rotors half as often and there is a little redundancy in case one brake caliper fails (but the brake pipe is still intact). But these seem to be rather small benefits.

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Two reasons:

First, braking power. The bike's deceleration is caused by the pads clamping onto the brake disks. With two disks and two sets of pads, there's more clamping available, and thus the bike can be decelerated more quickly. Because your bike can activate the ABS with one brake disk, the bike has sufficient braking capacity (assuming the manufacturer has set the ABS activation threshhold high enough).

Second, heat dissipation. Brakes heat up when used, and typically lose effectiveness. Your bike's single disk may work just fine in one stop, but it will perform less well on repeated ones. Trying a half-dozen stops from 60 mph to zero, one after the other, will almost assuredly result in the stopping distance becoming significantly longer. (Taken to an extreme, excess heat can also boil the brake fluid, which makes the brakes completely unusable.) Having two disks and two calipers and two sets of pads increases the mass being heated, and thus slows the increase in temperature which degrades braking, and thereby increases the braking system's resistance to this degradation.

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  • I do get the second reason, thank you. The first reason seems to be valid only if one brake would not provide enough braking power, which my single brake (200 kg Motorcycle) seems to do. So for similarly weighted motorcycles, there should not be an increase in braking power with to brakes, right? – Niklas May 18 '19 at 18:11
  • If the similar-weighted bikes had brakes of similar efficiency (i.e., the same squeeze on the brake lever yielded the same squeeze of the pads, and the pads and disks were of similar composition and thus created similar friction), then yes. – DavidSupportsMonica May 18 '19 at 19:38

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