Originally Posted by
AdelaaR
The reason why they have disc brakes on mountainbikes is because they ride in the mud ... and with muddy rims the typical rimbrakes will have reduced efficiency because the rims will be muddy.
Discs are located at the center of your wheel and so are less prone to getting full of mud.
For normal riding, however, there is almost no difference between any of the available braking systems because all of those systems brake better than your tire is able to have grip enough not to slip ... which means that your tire will slip on the road way before your brake will slip on the rim.
It's not just about the mud. Many of us avoid mud. Disc brakes for me are about perfect consistency and timing, and also an excellent ratio of braking power received in return a given amount of finger squeeze--call it "leverage".
I do have a nice set of rim brakes on the bike I've been riding most this summer. They are fantastic for a lot of the cross-country type riding I do. But when the going gets steep and/or gnarly, that's when they show limitation. Sometimes on a sketchy downhill one is picking one's way amongst roots and rocks
and trying to time the modulation of the front brake to coincide with usable patches of ground that might only be a few inches or a few feet long at most. One has weight back on the bike, hands on the grips, the mind is occupied with puzzling out the trail several steps ahead, and that is when the ability to squeeze the brake lever with a single finger and *know* with certainty what's going to happen and precisely *when* it will happen is critical. It is the difference between braking being a subconscious or a conscious activity.
The leverage from larger rotors helps too, in avoiding hand fatigue and allowing one to maintain a light grip on the bar. I have enough to do in those situations without having to suddenly reposition to put two fingers on the lever. Any mental bandwidth I'm forced to divert to braking is bandwidth lost from the much-needed route-finding that will get me safely to the bottom of the hill. The consistency, precision, and leverage from a good set of disc brakes allows speed-control to be relegated below the level of consciousness so I can focus on unlocking the trail ahead.
In a perfect, ideal, theoretical world one might get all the same advantages from rim brakes. With current parts on the market, I don't see that happening.
(There is also a "looks" factor. I readily acknowledge the role that appearance and style have played in the adoption of disc brakes. It is undeniable that many are drawn to them by their looks. I know I was at first, and looks are still a factor for me today. I admit it).