Will a disc wheel speed up your triathlon bike split or are they expensive, heavy, and hard to handle?
Disc wheels are solid or covered wheels designed to improve airflow around the rear end of the bike and reduce drag. They became popular in the early ’80s when Francesco Moser broke the cycling world hour record on the track riding front and rear discs. Triathletes were early adopters too, but disc wheel use is not as widespread as it is with dedicated time triallists, who prize aerodynamics above everything else. But are they really worth having for a triathlon race? How much aero difference is there between a disc and a normal wheel? Are they unmanageable in windy conditions? Doesn’t the extra weight slow you down on hills?
Here to answer all those questions and help you decide if a disc is the best wheel for you, is the editor of bike radar.com and one of the UK’s fastest cycle time-triallist, Jeff Jones.
There’s no getting away from the fact that disc wheels are heavier than their spoked counterparts; all that carbon must weigh something. Weights start from under 800g for a top-end disc and go up to 1,350g for something like a HED Jet. That may sound heavy when you can buy wheelsets that weigh as much as one disc, but in comparative terms when considering the entire bike and rider, an extra 500g will make very little performance difference. For general handling I prefer discs that weigh 1,000g or less but I’ve happily raced on a 1,200g wheel for years without a problem.
Disc wheels are more aerodynamic than spoked wheels and that means you will go faster when riding a disc than not, no matter what speed you ride at. How much faster really depends on what wheels you’re comparing them to and how fast you ride. As a rule of thumb, you could save between 30 seconds to two minutes in a 40km bike leg – and the slower you are, the more time you’ll save. I’ve heard of exceptions, such as the Reynolds RZR 46 and the Smart Enve 8.9 wheelsets, which are said to be faster than the ‘fastest’ wind tunnel-tested disc wheel, but I’ve yet to verify these claims
The biggest myth about disc wheels is that they are unmanageable in crosswinds. This is not true except for front discs – and you’d have to be suicidal to ride one of those on a windy day. A rear disc wheel will not react in the same way because it doesn’t sit under your steering axis, so it will only move as much as the rest of the bike does when subject to side forces. You will barely feel a difference compared with a normal spoked wheel. The real problem in crosswinds is with the front wheel, so don’t go too deep when it’s windy.
With prices starting from around £700 for a Corima disc and going up to around £2,000-plus, discs are not cheap. They’re probably one of the priciest performance upgrades you can make in terms of seconds saved for pounds spent. A good disc wheel will last you for years however, and give you plenty of satisfaction as you rumble along alerting other competitors to your presence. In aero terms, there’s not a huge amount of difference between discs. It’s usually a case of lighter weight costs more, so go for the one you can afford. If you are on a budget, you can now buy wheel covers that turn your spoked wheel into a disc and cost less than £100.
A disc wheel is usually the fastest option on a hilly course, but let’s qualify that: if the course has a lot of steep climbs (average five per cent or more), technical descents and not a lot of flat, then I’d opt for a pair of light, aero (50-60mm deep) wheels. It can be a tough call to decide what wheels to run unless you have pre-ridden the course: what looks bad on paper can be OK, and vice versa. My tip is to not discount a disc too readily.
So should you buy a disc wheel?
Disc wheels are performance boosters: get one and you should go faster. However, having a decent front wheel and aero helmet, good positioning on the bike and clothing that fits properly are even more important, and will save you more time per pound spent.
This article was originally published in Triathlon Plus magazine. Save time and money by having every issue delivered to your door or digital device by subscribing to the print edition or buying digitally through Zinio or Apple Newsstand.
You’ll find loads more triathlon news, reviews and insight at triradar.com