This post provides a short overview of advantages and disadvantages of bicycle disc brakes, compared to rim brakes (whether they are cantilever, road, or V-brakes). When comparing, it is understood that the brakes are of a good build quality and set up properly.
A separate article explains drum brake (& roller brake) pros and cons.
Update: if it helps anyone, I made a series of videos on hydraulic brake service.
It should be noted that there are two types of disc brakes: hydraulic and mechanical. Separate post(s) will explain the differences and the (mechanical) causes of disc brake advantages and disadvantages compared to rim brakes.
1. Advantages of disc brakes
- Greater stopping power – although the tyre grip is often the limiting factor, so there often isn’t a much shorter stopping distance caused by disc’s greater stopping power (the main reason for shorter stopping distance with disc brakes is explained in the next point). Exception are conditions with ice and snow, or mud, when disc brakes are superior.
- Better (more even) brake force modulation, especially when it’s wet and/or muddy.
- Hydraulic disc brakes automatically adjust brake pad distance (position) as the pads get worn – no need to manually adjust them. This is not the case with mechanical disc brakes though.
- They don’t wear the rims from braking – only pads and discs get worn, while the rim stays untouched, so there’s no need to re-lace a new rim after it gets worn from braking.
- If a wheel gets out of true (from some damage, broken spoke etc.), the brakes will not start rubbing or stop working properly.
2. Disadvantages of disc brakes
- They cause more load on the (front) fork blades and the steering column, because the brake caliper is anchored near the bottom of the forks. This calls for stronger (and heavier) forks.
- With front disc brakes, if a wheel (and the fork) doesn’t have a modern “through axle,” (it’s not technically an axle, but that’s for another time) braking force tends to pull the (front) wheel out of the dropouts. This requires the wheel to be tightened with more force in the dropouts and regular inspection whether it is still in place and not loosened.
For more details on this, see the “disc brake forks” chapter in my frame design article.
- The whole system is heavier than a rim brake system.
- Tendency of annoying rubbing of pads to the disc, due to very small clearance of pads from the discs (otherwise there would not be enough stopping power generated using the hand brake levers and a disc of relatively small diameter, without using a servo – principle of lever, same as explained for mechanical brakes). With motor vehicles, this rubbing can not be heard (engine sound and greater speeds), while the motor provides a lot more than human 100-300 watts, so the mechanical losses are negligible – this is not the case with bicycles. It is often the case when reinstalling a wheel (fixing a flat etc) that this rubbing occurs and some fine tuning is needed – again.
- Higher price
3. Disc brakes – yes, or no?
All the noted pros and cons are of objective, mechanical nature. Each cyclist must decide for themselves, based on their riding style, riding conditions and budget, whether disc, or rim brakes are an optimal choice for them. With the exception of (extremely) muddy and snowy conditions, all the good quality, properly set up brakes provide decent stopping power and modulation – whether they are disc, or rim brakes.
4. Author’s personal opinion
Disc brakes in cycling, with the exception of fast MTB off road riding in mud, especially down hill, are more a trend, marketing and money making invention, than an improvement. The main advantage: stopping power and modulation, is achieved using small pad to disc clearance (enabling a greater mechanical advantage when pulling a brake lever), and exactly that often causes pad rubbing – which is annoying and creates unacceptable drag. Human race has not yet produced disc brakes that do not rub. There were some experiments in auto industry, but only after realizing that rubbing is a necessary evil (that doesn’t cause any practical problems for motor vehicles), the disc brakes have shun with their full light (again, in motor vehicle industry).
Because of this, I think that, in cycling, disc brakes have a limited range where they should be chosen as an optimal solution – most of it is marketing and money making.
Chris Froome’s experience with disc brakes on his road bicycle:
Related post – Bicycle braking technique:
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