Wind Tunnel session with Drag2Zero

This is gonna be a bit dry if you’re not interested in bicycle aerodynamics…

Today I paid a visit to the Mercedes F1 wind tunnel in Brackley, Northants, for a session with Drag2Zero.  Paid being the operative word, as it ain’t cheap! 😀

The specific information given to customers in the tunnel is confidential, so I won’t be going into detail as to exactly what changes were made.  But I know a few people who read the blog are interested to hear about this jaunt, so I will explain my experience as much as I can.

I arrived nice and early for the scheduled two hour session.  The staff were very friendly and welcoming, and after a coffee and a quick glance through Rouleur magazine, I was introduced to the main man, Simon Smart.  As someone with a keen interest (but no technical nous) in bicycle aerodynamics, to me Simon is a figure who demands proper respect, as not only is he the chap who tells you how to go faster on your own bike, he’s also the designer of the Giant Trinity Advanced and Scott Plasma TT bikes, among other products.  Here’s a short video featuring Simon from the BBC website

We had a quick chat about my (limited) experience and Simon explained the protocol of the testing we would do.  Without going into too much detail we’d carry out a number of runs in the tunnel, each of approximately 5 minutes.  During each run, Simon would be measuring the amount of drag I caused in real time and the results would feed into the changes we made for the next run.  I got changed into my gimp suit and by the time I was ready my bike was mounted on their equipment in the tunnel.  

The testing rig sits in the wind tunnel on the ‘drag scales’ (my invented phrase), which as far as I can tell is a large horizontal pad that can measure the amount of drag that an object (i.e. me and my bike) suffers when sat on the pad in the wind flow.  It connects to the bike via a set of rollers on the front and rear wheels, and the bike is supported by elongated skewers through both wheel centres.  It’s like a cross between rollers and a turbo trainer.  My gears, and the resistance of the rollers, were set so I could spin the wheels at approximately 30mph with effort, but well below race pace (since I would be sat on the rig for 2 hours, although not pedalling all that time).  Simon explained that the wind would be set to 30mph and we would test at one yaw angle, which he said is the average yaw that a rider experiences at that speed.  Effectively this means that the rig is rotated by a number of degrees from the centreline of the wind flow.

I knew that to establish a baseline, the first run would need to be done in the position in which I have been racing.  So I was careful to ensure that I had adjusted the bike to exactly that position.  Obviously I was hoping that the position would prove so poor that the sound of the wind would be drowned out by the laughter of the technicians.  Any first time visitor to the tunnel surely wants to be told “your position is terrible, here have a couple of mph for free”.  Sadly that wasn’t the case.  Simon’s view on my position was that the CdA was about as low as I could expect to achieve, given my size.  I don’t yet know the absolute figure, because post-processing is required to remove the drag effect of the rig hardware, but Simon told me the figure was less than 0.2 (meaningless to most of you, I know).  I think his words were “It’s not quite exceptional, but it’s very good”.  Very good really means very bad.  It means big improvements in aerodynamics would not be found.  Somehow, quite by chance, I had found an aerodynamic position.  Damn.  This means I am not going to be a world beater.  If you need to, please take a moment to recover from the shock of that revelation 😉

If you’ve read my past postings on position, you might recall that in mid July I had lowered my saddle to the lowest position I could (reasonably) comfortably pedal in, and lowered the bars as far as they would go.  This was my amateur attempt at improving my aerodynamics.  The position was definitely faster (I PB’d by 30 seconds in my first 10 mile race after the change), but it cost me 10-15 watts of power (due probably to the very closed hip angle between thigh and torso).  Simon advised that if the drag effect of this position could not be improved within the scope of the session, we would focus on trying to find a position that would allow me to produce more power, with little or no extra drag cost.

In the main set of runs we tried various positions to see the effect on drag.  As Simon had predicted, we didn’t find one that significantly reduced drag.  We did however, manage to find a far less extreme position that was slightly better on drag.  It is to be hoped that this position releases a reasonable amount of power.  If so, that will be the material gain from the session.  It’s about power vs CdA after all.  Most folk would hope to improve CdA without harming power.  In my case, prior to the test, CdA happened to be very good, but in order to achieve that CdA, power output had degraded.  I am hopeful that my power output can be restored to what it was before I lowered the position so much in July.  I won’t know this until I can conduct a test, which may be a week or so, as the bike needs to be re-cabled in it’s new configuration.

We also tried some different things with the parts of the body that are not fixed to the contact points of the bike.  There’s two specific things that I have been trying to do this year to reduce frontal area (and hopefully drag).  We found that one of these things reduced drag, and the other one (which I find physically and mentally difficult to do) actually increased drag.  So I’m pleased to be able to stop trying to do that thing!  I am being cagey here due to confidentiality, but also these things are so specific to the individual that someone else might find the polar opposite if tested.

As for the whole experience, I had a really cool day.  The full force of the F1 wind tunnel technology and the technical know-how of Drag2Zero is brought to bear, for two hours, to try and make you faster.  It really does feel like you are the centre of their universe for those 120 minutes.  I felt as though they treated me as they would treat Tony Martin.  It’s expensive, and for me there was no silver bullet aerodynamically, but I hope and expect it to bear real fruit, and it was a very memorable experience.  I am due to receive a full technical report of the session (CD by post I think), most of which I won’t be able to share, but I will probably follow up with a post of my absolute CdA numbers from the best and initial positions.  A number of photos were taken during the session.  I’m not sure yet if I can post any of them, but if I can, I will.

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Posted on November 20, 2013, in Uncategorized and tagged , , , , , , , , . Bookmark the permalink. 2 Comments.

  1. As much as finding only a fractional amount of CdA savings might be disappointing, it’s also extremely reassuring to know for absolutely sure. I’ve always enjoyed your blog from over the pond here – keep it up!

    • Hi Eric. Thanks for the comment. Yeah the position question used to use up a lot of brain cycles. Now it uses up zero, except in trying to maintain the correct position on the turbo.

      I seem to have made some power gains on the turbo. But of course they are not yet realised where it matters. And also I can’t be sure if those gains are because of the position change, or because of more consistent training. Maybe both.

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