You must have seen this kind of “disc” wheel in the Olympics or the Tour de France time trial. The English name of this kind of wheel is disc wheel. It is generally called a closed wheel in China.

What is a closed wheel?

Unlike standard road bike wheels, closed wheels usually have no spokes, and the closed discs are usually made of carbon fiber, which is thinner and lighter. And its interior is usually composed of foam.

Rim depths are usually under 60mm for common road bike wheels, while 80mm rims are commonplace for closed wheels on TT time trial bikes. Simply, the deeper the wheel, the better the aerodynamics and the faster you’ll go.

How fast can a closed wheel go?

For high-speed bikes, wind resistance is the biggest obstacle, and closed wheels are more aerodynamic, and are almost always faster than traditional shallow-spoke wheels, except in hilly or windy conditions. Extensive testing has shown that closed wheels are up to 2 minutes faster per hour than standard wheels. Road bikes with closed wheels front and rear are faster, but the UCI prohibits bikes with closed wheels on the front and rear, so you don’t see pro riders racing with double closed wheels.

What are the advantages and disadvantages of closed wheels?

Pros: More aerodynamic, minimizes drag and turbulence from spokes compared to conventional wheels. On flat, windless roads, closed wheels are faster, and when going downhill, the advantages of closed wheels are greater. At the same time, the closed wheel is aesthetically pleasing (beautiful indeed).

Disadvantages: Closed wheels are heavier than normal wheels, so they are more difficult to use on climbs (theoretically, but Chris Boardman has won a hill climb championship with rear closed wheels).

Wind has a big impact on closed wheels, and strong crosswinds can cause unstable handling, slow riders down, and even cause accidents. This effect also has its benefits. If a crosswind hits the bike at an angle below 45 degrees, the “sail” effect can benefit the rider by pushing the rider forward.

Closed wheels are not durable, most closed wheels are made of carbon fiber with a foam type inside. Hitting a pothole would spell disaster for a disc wheel. At the same time the closed wheel is almost impossible to repair completely.

Closed wheels are more expensive and use more high-end materials after all.

Closed wheels are not suitable for large-scale races of all kinds, and are very dangerous to use in crowds as they can amplify any contact the riders have with each other as they fight for position, resulting in accidents. For this reason, they are expressly banned by the UCI from participating in any large-scale competition.