20 Oct 2020
FROM RIM TO DISC BRAKE: HOW HAVE WHEELS CHANGED?
The introduction of the disc brake has brought with it many changes to take advantage of this powerful new braking system. Wheels are one of the components that required a complete overhaul with the introduction of the rotor, mainly the removal of a braking surface on the sidewall of the rim and the introduction of a rotor mounting system on the hubs. Likewise, the disc brake has also changed riding styles – allowing you to enter corners faster and brake later than ever before!
How have disc brake wheels changed compared with traditional rim brake wheels?
1) NEW DISTRIBUTION OF FORCES
With the widespread acceptance and move to disc brake there has been a change in how braking forces are transmitted and distributed to the wheels. In a rim brake wheel, the forces are symmetrically distributed through the center of the wheel with the brake caliper uniformly grabbing the rim on each side at the brake track. With disc brakes, we see that the forces on the wheel have changed dramatically – moving the load from the central rim location to one side of the hub with the rotor absorbing the initial braking forces and then transferring through the hub, spokes, rim and then to tires. This change in forces has resulted in a change of the parts of the wheel system.
2) HOW THE RIM HAS CHANGED
Here at Vision we like to speak about the “aerodynamic weight” of a wheel. By eliminating the need for a brake track on the rim, our attention to aerodynamics has led to the creation of rims with a wider tire bed and a decidedly more rounded and contoured shape which inevitably require the use of larger quantities of composite. Thanks to these new generation rims, these "modern" wheels not only perform better aerodynamically but, especially with every-day riders, they are also more stable, safer and easier to handle in a variety of wind conditions. This is all accomplished without a dramatic increase in weight. In the case of the Metron 55 SL for example, a pair of traditional rim brake TL/CL version weighs 1580 grams while the disc brake version weighs 1630 grams.
3) THE KEY ROLE OF HUBS
With the introduction of the disc brake, hubs have become an even more important part of wheel performance. Hubs in rim brake wheels only had to roll smooth and be light. With disc brakes, the hubs not only need to roll smooth and be light, but they are now taking the initial braking forces applied to the wheel. An increase in hub shell diameter to support through-axles, rotor mounting and withstand braking forces results in a stiffer, more efficient performing hub.
4) AND WHAT ABOUT SPOKES?
The change to disc brakes also affects the spokes needed in a wheel. This is most obvious on the front wheel where the rotor creates a dish in the wheel while the need to withstand braking forces results in an increased spoke count and different lacing pattern. The rear wheel, while having less impact, will also see an increase in spoke count to withstand braking forces. In the case of the Vision Metron 55 SL, for example, the rim brake model has 16 spokes on the front and 21 on the rear, while the disc brake model has 21 at the front and 24 at the rear.
As you can see there are many differences between rim and disc brake wheels. Along with these technical features, there are several sales points that we would like to leave you with. With disc brake wheels, there is a significant increase in braking power in both wet and dry conditions that will make cycling safer. By eliminating the braking surface on the rim itself, disc brake wheelsets will last much longer than a traditional rim brake wheel. Finally, reducing the weight in the rim and moving it to the hub makes for wheels that roll-up to speed faster and with less effort, keeping rider fatigue down over the course of your ride.
Enjoy all of these benefits in FSA and Visions disc brake wheel line-ups!