Technique

A beginner’s guide to aerodynamics – and why it’s so important to cycling

If you want to go fast, you need to understand aerodynamics. Here's are guide on why it's more important to evade than try and overpower the wind

Aerodynamics and equipment

Aerodynamics have become more an more prominent in cycling over the last few years, and are no longer just the domain of the time trialist
Whether your in the velodrome or on the road, aerodynamics are a key limiting factor in how quickly you'll be able to ride (pic: Alex Whitehead/SWpix)
No matter what, when you're riding on your own it's far more efficient to try and get out of the way of the air than attempt to overpower it
The best way to measure aerodynamics and the drag your produce as a rider is to test in a wind tunnel (pic: Endura)
Every bit of kit these days seems to come with a claimed aero gain over a certain distance at a certain speed, but how much of that translates to the speed at which you ride?

Aerodynamics and equipment

When you go to buy a set of wheels, a helmet, skinsuit or even a set of shoes many manufacturers give an indication of how many seconds that bit of equipment will save you over a given distance. More confusingly, the speed at which those savings can be found varies and, amusingly, it’s often up to 50kph – a speed which I tend to only achieve going downhill…

So how seriously should you take those claims? If a wheel manufacturer, for example, says their wheels will save you 90secs over a 40km TT ridden at 50kph, what does that mean for the rest of us who’ll be riding significantly slower? I asked Dr Marshall this and below are some figures he supplied to give you an idea of how those gains change with speed:

“Basically, percentage-wise, it stays consistent so a 17 percent reduction in C_DA gives a 17 percent reduction in power required for each velocity,” he explains.

“To put that into perspective if the rider with a C_DA of 0.3 improved his aerodynamics to reduce that value to 0.25, but maintained the 492watt output he could increase his velocity from 50kph to over 53kph and save two and a half minutes over a 40km time trial – assuming of course constant straight speed on a straight and level road with no ambient wind.

“On the other hand, there are Reynolds number effects whereby the aerodynamics of a body will change depending on the flow velocity and hence Reynolds number (a non-dimensional number used to gauge intertial:viscous forces in a flow).

“In simple terms what this means is that what works at one velocity – be it a helmet, skinsuit, wheel or anything else exposed to the flow) will not necessarily be the best option at a different velocity so creating a ‘package’ for a given rider at a given velocity is important.”

What that means is that it’s more complicated than simply going out and buying the product in each category that claims to save the most time and hoping to aggregate all those gains. So what works for you at one velocity may not work as well at another, so it really is a case of trial and error (ideally in measureable wind tunnel conditions) if you want to know what your absolute best setup is.