Originally Posted by
luddite_68
I know this sounds really dumb, but aren't rim brakes just really big mechanical disc brakes?
There are hydraulic rim brakes too.
While you’re right for a certain level of generalization, the devil is in the details.
The main advantage that discs have lies in the amount of travel needed to overcome slop and flex.
For discs, 2 mm of pad travel (or even less) is all that is required to go from brake unengaged to wheel lock.
For rim brakes, 2 mm travel would only take you from unengaged to touching lightly.
Then there’s the flex. A disc brake caliper is a small, rigid assembly. There isn’t any obvious flex anywhere. Rim brakes, there are several parts that’ll flex enough to be visible to the naked eye.
Regardless of brake system, rider’s hands remain the same size, so there’s the same amount of travel available at that end. With a tighter/stiffer brake system, more of the travel can be traded for greater pinch force, giving more braking for a certain amount of hand effort.