When rim brakes and disc brakes alternate, many riders have already raised the question of whether disc brakes have greater wind resistance. As everyone knows, adding a disc brake system near the hub does increase wind resistance, but how much is the difference? Did you know there is also a difference in air resistance between bike discs?
Test 1: Disc Brakes vs Rim Brakes, and Disc Brake Size
Although the brake system actually increases the wind resistance of the hub area, the wheelset, tires, and discs should be considered as a whole. Since the shape of the rim is not limited by the brake edge, the degree of freedom in optimizing the rim shape/tire joint surface is greater, and compatibility with wide tires is better. Undoubtedly, in terms of the aerodynamic data of the rim, disc brakes can be pulled. Back to the game.
The results showed that with the most common 160mm rotors, disc brakes were less than 1 watt higher than rim brake wheels of the same size. If you change to a 140mm disc, the difference is 0.3 watts, which is almost negligible. If the disc is not installed, the wind resistance of the actual disc brake wheel is 0.6 watts lower. This result reflects the aerodynamic gain brought about by the ring shape optimization.
This test just shows the difference between the wheels, if the disc brake frame can get more than a 1-watt advantage through a more aggressive aero design (full internal cable routing, wide front and rear fork and crown design, etc.), then the disc brake The whole system will be faster than rim brakes.
Test 2: Disc shape design
In addition to the disc size, different discs also have a slight effect on the aerodynamic effect. Generally, manufacturers will emphasize the heat dissipation effect of their own discs, and there is no aerodynamic data.