Disc wheels are banned in some competitions to minimize the chances of accidents caused by the wind.
Disc wheels are solid and could act as a boat sail. If there’s extreme side wind, the rider could lose control of the bike and fall.
According to many, however, the dangers are blown out of proportion and very low when the disc wheel is at the back of the bike.
What is a disc wheel?
There are two types of disc wheels – solid (dedicated) and covered. In the first case, the disc wheel is made out of a mold designed with fairly complex software. The mold is either steel or aluminum, but the material used for the wheel is carbon in most cases. (The goal is, of course, to save weight.)
The wheel is put in an oven to harden the material before installing a hub and rim.
The other way to acquire a disc wheel is to cover a regular spoke wheel with a disc cover. The cover is attached to the spokes and gives most of the benefits of a regular disc wheel.
The downside of disc wheel covers is the added weight – usually between 200 and 400 grams (7-14oz). In the world of fast riding, this is considered a lot, especially when you account for the fact that molded disc wheels could weigh as much as the covers.
Why are disc wheels banned from some competitions?
Disc wheels are banned from some outdoor competitions because strong crosswinds can affect the bike’s handling.
If the rider is fairly heavy and there’s only a disc wheel at the back, the handling is unlikely to suffer to a notable degree. However, if there’s a disc wheel at the front too, even a heavy rider can experience severe handling issues. The rider will have to fight the wind via the handlebars.
The modern aero bars found on time trial bikes amplify the negative effect. Aero bars allow the rider to assume a maximally aero position but greatly reduce the control over the handlebars.
Also, aero bars make it much harder to right in a straight line because the arms are very close to each other and thus have low leverage against the handlebars and respectively the fork. As with disc wheels, cross-winds exacerbate the problem.
This is one of the reasons why you won’t see aero bars in classic road cycling competitions.
The UCI (Union Cycliste Internationale) has banned aero bars when riding in tight groups because the profile of the bars can result in contact and thus a collision.
The most popular competition that has banned disc wheels is the IRONMAN World Championship. The Ironman World Championship is an annual triathlon event held in Hawaii, United States since 1978. (read more)
Here’s what the official website of the competition says regarding disc wheels:
For reasons of safety, solid (disc) rear wheels are prohibited at the IRONMAN World Championship;
Wheels of spoke construction may consist of an aero rim with spokes (spokes may be bladed, round, flattened, or oval); and
No wheel may contain any mechanism capable of accelerating or artificially causing the continued rotation of the wheel. (DSQ)read more
Why is a disc wheel used?
The main purpose for the existence of disc wheels is to make the bike more aerodynamic. Even aero spokes create a certain amount of drag with each wheel revolution because they protrude outside the tire and rim.
In different, discs stay within the width of the tire. As a result, disc wheels don’t have a significant if any contribution to wheel drag.
When did disc wheels become popular?
During the early 1980s, disc wheels gained popularity when the Italian rider Francesco Moser broke the Cycling World Hour Record using front and rear disc wheels.
Moser’s hour record was 51.151 km (1984) and took down Eddy Merckx’s 1972 record (49.431km). Ever since riders competing in the discipline have relied on disc wheels to benefit from the lighter weight and improved aerodynamics.
Filippo Ganna, an Italian professional road and track cyclist holds the current one-hour cycling record – 56.792 kilometers. He set the record On October 8, 2022, on a Pinarello Bolide with front and rear disc wheels.
However, it’s essential to specify that this competition takes place in an indoor velodrome where the negative effect of crosswinds is not present, and thus the risk of using disc wheels is minimized.