Bike Fitting

Aero optimisation in the wind tunnel

In a recent blog post I wrote about #freespeed, the hacks, changes and ways to go faster for no more physical effort! As a few people reminded me, “It’s not ‘free’, it’s going to cost you money”! But, if you are serious about maximising your potential in triathlon or time trialling its an area you can ill afford to ignore. You can read my blog on kit and the hacks you can take here. This article takes you though my recent experience of using a wind tunnel for aero gains.

One comment I reiterate throughout that previous kit post is the need to get a proper aerodynamic bike fit. I ride for the AeroCoach race team and also run outdoor aero testing sessions, for AeroCoach at Scunthorpe. You can find details of the type of sessions here. The reason I am passionate about offering this is I am keen to maximise my (limited) athletic ability and go as fast as possible using the best available knowledge.

Why wouldn’t you?

Many people spend so many thousands of pounds on bikes, yet don’t get an aero fit on a TT / Tri bike.  I can’t understand it.  I always use the same analogy,  If you went to Saville Row for a suit, you’d NEVER buy off the peg, you’d get it fitted. Bikes are the same.

There are many types of aero testing session available, depending on your budget and locality. But they all simply try to do the same thing, make you faster for the same power output.

There are reams of detailed posts about the exact savings you will see, how to calculate CDA, what an X% change in CDA means etc etc. This article isn’t another one of those. What I want to do is discuss it from a competitors perspective and hopefully, help you see why it’s relevant for you. I also want to run through what actually happens during an aero optimisation session in a wind tunnel.

Aero testing in the wind tunnel

The background to my aero wind tunnel session

I’ve been racing TT and Triathlon for over 15 years now. When I started hardly anyone, outside of Chris Boardman and Graham Obree’s efforts, and the US Postal F1 project, seemed to be know, or work on aerodynamics.

It was a pretty simple sport really. The rider with most power in those legs went fastest on the bike! It was great for me. I’ve always been a powerful rider and quickly found my bike legs in Tri and TT races to be right up there. I found the picture below recently. It’s from around the 2010 season I think – look at that position!

Aerodynamic bike fitting

Yet I probably won more races than I have done the last 2 years combined!

So what’s happened?  Put simply, the UK time trial scene has become THE most advanced testing ground for real world cycle aerodynamics.  Forward motion, speed, is a function of three things:

  1. Power through the pedals
  2. Mechanical loss whilst that power is transferred to forward motion
  3. The effort of pushing through the air

Until relatively recently all anyone was interested in was point 1. Training and coaching was all about increasing power. Over the last few years riders in the domestic TT scene such as Michael Hutchinson and Matt Bottrill pioneered the ‘total speed’ approach and looked at the problem from the 3 points above. This lead to huge success for them both.

Over these years others have copied, emulated and replicated the testing and work they did. Also aero optimisation services are more widely available, such as those pioneered by AeroCoach. And now with the Boardman wind tunnel being available in Evesham, the cost of aero testing has also fallen.

The sum total of this means, that in any Sunday TT, or Summer Triathlon a decent percentage of the best riders will have optimised their position via aero testing. The only realistic way to compete is to do as they do.

Many of us use Strava. You will see riders going 1/2/3+ minutes more than you in a race off LESS power. The reason is they are more aerodynamic! To improve your 25m TT time, or Olympic Triathlon time by a minute, you need to either produce about 20w more power OR save 20w via aero advantages to reduce mechanical loss (as in the last Blog) or ‘save’ 20w by reducing your aerodynamic drag.

Any decent coach will tell you, that for a relatively well trained athlete, gaining 20w (anywhere between 5-10% on your FTP) is a big ask. So #freespeed is the logical answer.

Aero optimisation in a wind tunnel

How do you achieve an aero advantage?

There are probably four approaches to take:

  1. A static fit from an experienced fitter
  2. An outdoor data validated test, ideally on a velodrome
  3. An indoor velodrome data validated test
  4. A wind tunnel

Needless to say, I have done the first three of these lots of times!  But I hadn’t been in a wind tunnel. So I am going to walk you through, in a bit of detail, my most recent aero test at the Boardman wind tunnel with AeroCoach. But firstly, the below points are worth remembering!

Things to remember when aero optimisation testing and bike fitting

  1. Every time you change your bike you will need to retest. Frame angles are different as are frame sizes and trying to copy a position between different bikes, particularly manufacturers is nigh on impossible.
  2. A different saddle can massively affect your aerodynamics – so be careful swapping around all the time!
  3. Bikes don’t make a massive difference. There may be 10w difference in drag (about 30secs in a 25m TT) between the best and worst (*well set up) TT bikes. EVEN so this doesn’t necessarily mean you will be able to get a great position on the ‘best aero bike’. Focus on the best position on YOUR bike.
  4. Power output is a compromise. The best aero position may not enable you to generate the most power. For me, a lower seat makes my aerodynamics way better. BUT I can’t generate the power. The right balance is what is the tipping point between loss of power and improvement in aerodynamics?
  5. Now (winter) is the ideal time to take an aero test. Why?  You have all winter to adapt to it on the turbo, testing and changing your position massively the day before a race is probably not optimal (I have done that many times too!).
  6. Your ‘best aerodynamic position’ will be an evolution. It’s very unlikely you will nail everything in one session. This is really important to remember. Any of the ‘best out there’ will have been through numerous fits where their position has evolved.
  7. Helmets make a huge difference. See the image below. Notice the gap between the helmet and my back? Having the helmet like in the photo versus rotating it back on my head to close that gap ‘costs’ me +5w. So to go at the same speed, I’d need 5 watts more power in the photo below versus a neatly ‘joined’ helmet to my back.
    Aero testing in a wind tunnel

The actual aero wind tunnel session

The Boardman Performance Centre is very impressive. There is a massive bike showroom and as you go upstairs there’s some great memorabilia from Chris Boardman’s racing days.

The wind tunnel itself is relatively small in the actual ‘working area’ but the surrounding air intake, fans and supporting paraphernalia are huge!

The bikes are set up on a ‘rolling road’ and clamped to the floor. Air is then ‘sucked’ over the rider.  What is weird, is you’d expect the fan to be in front of you. But it’s not. It’s situated behind you, as seen in the picture below.

Wind tunnel aero optimisation
At the wind tunnel session you will then run through a protocol to help improve your aero position. I went with two clear things in mind following my own review of my recent season.

I was pretty aerodynamic BUT my position for the season had compromised power. This was fine in long races where power is less important and staying aero and being comfortable is. However, in shorter distance races I was anywhere from 10-12% less powerful from where I know I can perform. So my challenge to Xav and his AeroCoach team was to optimise my long and short distance position.

Aero bike optimisation in a wind tunnel
Firstly we reviewed the bikes on their own. How many watts did it take to actually move the bike forward? Which one was most ‘aero’ in the wind tunnel?  Following this we started looking to achieve a short distance position, to get my power back. So what quickly became evident was that we could get to one optimum position that would maintain or improve my aerodynamics AND give me some power back. Happy days!

Wind tunnel aero testing

Over the space of three hours in the wind tunnel we moved through numerous protocols and settled on an aero position that we felt achieved both objectives. Check out this quick video from AeroCoach about the session.

Aerotest Video

Aero testing in a wind tunnel
Aero testing in a wind tunnel

So in summary:

  1. No matter how powerful you are you will be very unlikely to get a truly ‘fast’ position without some type of validation.
  2. A good static bike fit can go a long way to helping you optimise aerodynamics.
    1. I follow a number of bike fitters on Facebook who make wild claims of the amount of watts the new position they have set someone up in will save. This is total BS. They cannot ‘know’. An experienced ‘eye’ and a good fitter can help achieve a really good position on a static jig. The photo below shows a client of mine, Chris Day. We achieved his position on a static bike fit jig and we know from his performances how much faster he is. BUT I cannot tell how many watts we have actually bike fitting and testing using a wide tunnel
    2. Many fitters use the RETUL system (once a stand alone system and marketed as the ‘best available’ but now owned by Specialized).  This produces a bio mechanically efficient position, but without exception, every one that I have seen and tested are not aero-optimised. Think carefully about your priorities in a bike fit.
  3. Aerodynamics can be a compromise between power and the best aero position.
  4. Your best aerodynamic position will be an evolution and it will likely take a couple of sessions to optimise everything.
  5. Think of the three key facets of ‘speed’ and work on them all equally. Depending on where you are in your athletic development you may find much bigger gains out of 2 & 3, than trying to get more power.
    1. Power
    2. Mechanical loss
    3. Aerodynamics
  6. When you change any contact points on the bike you will have affected your aerodynamics – be very careful!
  7. Don’t just buy a helmet or skinsuit because so and so rides fast in it. You need to KNOW what will make YOU fast.
  8. Use the expertise out there. There is lots of it!


I hope you have found this useful and if you want to discuss more about aero bike fitting and using a wind tunnel please get in touch.



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