But these days you’ll see plenty of instances of them being used by road riders too. These cyclists have realised that they too could benefit from that same reduction in work – or an increase in speed for the same level of work – by reducing overall aerodynamic drag.
Aside from making yourself physically smaller (the less area you’re pushing into the wind, the less air you have to push out of the way), one of the most crucial areas on a bike when it comes to drag are the wheels. This is because of their relatively complex shape – the spokes – and the fact that they don’t just move forwards, but rotate in order to do so.
Aero wheels: Points to consider
Aero shape: The design has to control the air passing over the whole wheel while it rotates. It must also be strong enough to last, or be sufficiently tough as a rim if it’s structural. At the same time it has to behave in side winds and not steer the bike around too much.
Brake track: Under hard or long braking a lot of heat can be exchanged (brakes turn kinetic energy into heat). The rim has to be able to handle it, and that includes any glue or resins used to bond carbon to aluminium alloy, or the carbon and resin if it’s a full carbon rim.
Spokes: A good rule is that fewer spokes make a more aerodynamic wheel, but there have to be enough to make the wheel sufficiently strong and stiff. And they don’t have to be aero shaped: round section spokes aren’t the disadvantage some people think they are. Straight-pull spokes give higher tension, and traditional J-bend spokes allow easy replacement. Spokes anchored into the outer edge of the rim add security, while others fix spokes to the inside edge for easier truing.
Rim depth: When it comes to ideal aero rim sizes, anything between 45-60mm tends to hit a sweet spot for aerodynamics versus handling, though this isn’t a rule set in stone. Shallower rims (30mm deep) can give good benefits over standard wheels too, and are less influenced by side winds.
Tyres: Clinchers are the easiest to repair with an inner tube and best for day in, day out riding. Tubulars have to be glued onto the rim but are less prone to pinch flats. Rolling resistance varies, depending on the tyre, however there's plenty of data that shows the best clinchers are equivalent to the best tubulars in this area of tyre performance.
Hubs: What matters is what’s going on inside the hub. If these will only be sunny-day specials, sealing doesn’t matter as much as if you’re going to be using them whatever the weather. The pick-up speed of the freehub and how much noise it makes, and whether you get fancy skewers, can also be a ‘make or break’ aspect for some riders.