Wheels are possibly the most visible performance oriented change you can make to your bike. Unfortunately there seems to be a general assumption that more expensive and/or lighter equals faster.
I’ve also heard athletes quoting outlandish figures for the speed benefits of race wheels and the maxim I mentioned last week – the terrible advice that it is better to put race wheels on a road bike for Ironman than to buy a TT bike. So today I shall look at the impact of wheel choice.
Hed Cycling have long been very helpful in providing aero data for their wheels. Which, as is my habit, I have extracted and analysed. I should note that they haven’t provided full information about test protocol so the data is not as useful as it might be but it serves well as an indication of benefits.
Exhibit A is a comparison of what Hed calls a standard OE wheel (this is one of the points that hasn’t been clarified – exactly what is a ‘standard’ wheel?) to their 40, 60 and 90mm clincher offerings. I used the Ironman Kona model with the light wind conditions seen in 2013.
It’s clear that wheels do make a difference – in this example by ~0.4kph (0.25mph).
Next we consider the more normal conditions seen in 2012 at Kona. This is when deep carbon wheels show their worth. Unfortunately high winds are also when most people start looking for shallower options for fear of the buffeting they will receive in crosswinds.
It’s worth noting that most race wheels have fairly similar performance in light winds – the first chart shows ~1min difference over 180km for wheels that differ in depth by 50mm (2″, aka quite a lot). Where the best wheels set themselves apart is performance in the wind.
Now the sharp eyed reader might notice that the shallowest Hed wheel considered above is 40mm and it may occur to them that there are alloy wheels near or at that depth. So we’ll look at some data that Tour Magazine collected for alloy wheels.
In this case we know what the standard wheel is – a 32h Mavic Open Pro (19mm deep) – what was considered a proper training wheel in the not too distant past.
At first glance this looks embarassing for the Hed wheels. But I’ve heard rumours that the Hed Standard OE wheel was actually the Mavic Ksyrium which would put the performance of the Mavic Cosmic Elite into perspective.
Nonetheless – it’s clear that going for a 30mm aero profiled wheel with low spoke count (like the Cosmic Elite) gives you a nice chunk of the advantage that deep carbon wheels offer. Which is why I often advise my clients that getting a set of 30mm alloy wheels is a good path towards addressing the low hanging fruit for wheels.
For a road cyclist the figures above are discounted by being in a pack. As shown in the previous article (about frames) the aero advantages of wheels come during high speed crunch points of the race.
Everyone loves light wheels – they make a bike feel snappy to ride and impressive to hoist. However, weight only impacts in a significant way on very steep climbs. The figures given by the model above take weight differences into account so obviously aero benefits outweigh weight benefits when looking at whole courses. Thus a rider seeking speed needs to focus on wheel aerodynamics with weight as a secondary consideration.
To conclude – wheels do make a difference to speed (and feel) and can provide a mental boost (my bike is dressed to race!). But they don’t need to be expensive and carbon to provide a nice benefit. I haven’t discussed looking for maximum performance in this article (as usual because I’m trying to be brief) but it is inadvisable to simply assume that more expensive is better.