Why do disc brakes stop faster in dry conditions? 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:



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.
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..