At the suggestion of my friends at Sweat7 I’m starting a ‘Marginal Gains Monday’ post to work alongside their series of the same name. The aim is to briefly cover one topic to provide readers with some useful information about hunting out small advantages.
Having been in the Wind Tunnel again last week I’m going to discuss the changes in aerodynamics possible by changing your body position on the bike.
For those who’ve not heard this before it will be interesting and for those who have – it bears repeating:
Approximately 80% of your total air resistance comes from your body
That means that all the agonising about frames and wheels is only acting on ~20% of the total package. So a 5% improvement in equipment aerodynamics would lead to a 1% improvement (0.05 x 0.2) overall. And 5% is a pretty big gain for equipment. On the other hand – a 1.25% improvement in body drag gives the same 1% improvement overall. I have measured body aero drag improvements for my clients of up to 15% (of overall drag) – you cannot achieve those sort of gains with equipment unless you’re road racing on a downhill MTB currently.
Not only is there a lot more scope for improvement with position it’s also usually cheaper than buying equipment (unless your current equipment limits your position).
Most people assume that improving their aero drag is going to require lowering the bars by an obscene amount. And yes, lowering the bars is often required to achieve a faster position. But not always.
I have a couple of useful examples:
To the left is a before/after overlay (blue is after) for one of my clients from a recent windtunnel session. I was able to help the client reduce their drag by 8%. This is a lot – it translates to over a minute gained in a 40km or 5-10mins in an Ironman (depending on how fast you’re going).
This did not require massive changes. Just a 1cm increase in drop (from saddle to bars) and a lengthening of the aerobars. You can see from the silhouette that it was overall just a small alteration.
While the changes were small they were significant in altering the way the wind flowed around the rider,
Then we made further gains with helmet selection, but that is a topic for another day.
Another example that I can’t do the overlay on (pictures were from slightly different angles but the silhouettes still demonstrate the point:
Unfortunately I was inconsistent with the colours and blue is the before shot this time (I was also a bit lazy about clear cutting the wheels but they’re not the focus here).
This rider reduced their aero drag by 15% with no change in bar height. There were significant changes in bar setup and reach to the bars. It’s clear in the images that the rider was able to significantly lower their head – thus reducing frontal area.
Ultimately working on position is your best chance for making significant changes in aerodynamic performance. As long as your current bike is not limiting your position options it needn’t be any expensive process. And as you can see from the examples given above – getting more aero doesn’t necessarily require getting crazily low. What it does require is having the fundamentals of your position sorted and then having a plan to continue adapting (and preferably testing to determine what is fastest for you) – this is where an experienced bike fitter can add value.
In some ways position is not really marginal gains. They can be massive gains – for new clients I’m usually aiming for more comfortable and more aero which is quite a nice combo.