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I have heard that bikes with disc brakes have shorter stopping distances even in dry conditions, such as the comparison in this video: GCN - How Much Faster Can You Stop With Disc Brakes?

At about 1:30, on a dry gravel road, the bike with disc brakes stops 2 meters sooner:

two bikes profile view, with the rim brakes bike about 2 meters in front

My understanding based on car tires is that stopping distance is a function of the tires' traction with the ground and whether the driver/ABS can avoid locking up the wheels (source). While there are higher end cars with fancier braking (e.g. disc brakes on all wheels, or bigger brakes), the main benefit is dissipating heat faster under repeated braking.

Is it because disc brakes allow wider tires which have a bigger contact patch? Or do I have an incorrect assumption - maybe stopping distance is not traction limited in bikes? Thank you.

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    the two riders are clearly not even using the same technique with the same execution in terms of where they place their body weight, let alone slight differences in their reaction time, to account for 2m from 40kph?
    – Affe
    Feb 18, 2021 at 20:51
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    @Affe Indeed. It sure seems the rider with the disc brakes shifts his weight considerably farther back when braking than the rider using rim brakes does. I also love how the disc brake bike also seems to come to a sudden stop each time while the rim brake bike seems to coast into a stop. If you look closely at that video, it sure seems like the books are cooked in favor of disc brakes.
    – Andrew Henle
    Feb 18, 2021 at 21:56
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    GCN shows, and their challenges, while entertaining, lack a lot of rigor that true science demands. Don't take their results too seriously.
    – whatsisname
    Feb 19, 2021 at 1:27

1 Answer 1

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No, the stopping distance is not just traction limited - or at least not just by the wheel/road surface combination. Even if you can block your wheel with your rim brakes and get the wheel slipped, you might be able to stop faster with better modulation when you actually avoid the slip. The consistency in breaking in the disc brakes helps to predict the exact force necessary.

Also, the raw power is definitely bigger, there is no question about it..

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