The shallow rims your bike came with might look smart but, when it comes to air flow, the breaks in the surface cause a big ol’ mess. The wheel’s leading-edge cuts through the air, which then comes back together in a turbulent fashion – increasing drag.
Deep section rims on the other hand are crafted with a curved, air foil shape for added aerodynamic advantage. This surface allows the air to re-join smoothly. Not only can this reduce drag, but it produces a forward-thrusting effect too.
Why are deep-section aero wheels faster?
Race wheels: 4 things to consider before buying
Are deep-section race wheels suitable for every triathlon course?
The short answer is no. Check the course topography and elevation. On a fast, flat profile a deep-section wheel can come into its own. The more wind-cheating your rims, the easier it’ll be to maintain momentum – shaving off time while saving energy for the run without losing speed.
Opting for deep rims on a hilly course on the other hand might just slow you down. While deep wheels create less drag, they’re heavier on the ups. More wheel can mean more weight – so it’s about balancing the aero advantage of a deeper wheel choice with the reduced weight of a shallow option. Don’t be put off by a couple of short hills, though, the time you’ll lose on the ups with weightier rims can be far outweighed by the time gained on the descents and flats.
If you’re on a flat course, the savings can really mount up – especially over a long-distance event. The aero advantage of deeper rims over shorter events is less noticeable since the course is more likely to have shorter stretches, lower overall speeds and more technical aspects – consider the Brownlees’ 58mm Zipps at Olympic distance versus Daniela Ryf’s 80mm DT Swiss’ at Ironman.
Does different weather conditions impact deep-section race wheels?
Check the average conditions in advance and forecast nearer the time – especially for the wind, which can catch you out in an otherwise perfectly suitable location; Kona and Lanzarote for example are notoriously windy courses.
Wind and deep-section wheels are not your friend – mostly. While tailwinds can be a welcome treat, cross winds or strong gusts will be far harder to handle with deep section, or worse disc, wheels.
The effect of wind is noticeably worse on the front than the rear wheel, and worse still if you’re relatively light. Aside from the fact that it’s scary or dangerous to be blown around in the wind, it also wastes the energy and momentum you could have gained with a pair of shallow rims.
What about riding style? Will a set of deep-section race wheels help every triathlete?
Deep rims and disc wheels come into their own at higher speeds. While at any speed they’ll look fancy, if you’re not a whippet then it’s worth considering carefully whether the extra wheel weight and cost is worth the advantage. If you’re racing fast over long stretches, though, the disc can serve you well.
What about race rules?
Think you’ve got the perfect wheel choice for your course profile and conditions? Don’t forget to check race rules. Draft legal events reduce the need for deep rims, while disc wheels will get you a DSQ at some events. British age group triathlon, for example, bans the use of disc wheels at all events – though deep-section wheels are allowed.
But just how long will the wheels last?
The answer is, if you’ve got disc brakes, probably longer. Your precious carbon wheel will wear out faster with rim brakes. Then again, the memory of being ‘that’ triathlete making the whooshing noise and sailing through draft zone after draft zone will last forever…