Aerodynamics – The key to going fast on the bike

Posted: August 8, 2011 in Time Trial Bikes, Triathlon

This is the first year that I have properly entered into the world of time trialing on the bike and I have learned ALOT.  Things started out pretty good and I won the first two races (Maidenhead & Brill Hilly).  This was a massive surprise to me as I consider myself big for a cyclist (weighing in at 84 kg) and would not have expected to do well on hilly courses. The next two TT’s I did were on flat courses and I did OK coming 2nd and 3rd in those two races.  What surprised me was that the gap between myself and the same riders from the hilly races was much smaller.  I would have expected it to be the other way around and put more time into the same people on the flatter courses.  Since both my bike and wheels are aerodynamically top notch,  this made me question just how aerodynamic my position was on the bike really was? The next TT of the year was the national 50.  I went into this not really sure what to expect.  Having no real experience in flat out 50 mile racing pace judgement was difficult.  I managed to hold 343 Watts average, but in hindsight massively undercooked it.  As I headed off for a run after the race my legs still felt fresh.  When I got back from the run I was chatting to a couple of guys who finished in the top 10 and rode about 7mins faster than me.  What really surprised me was I had put out 20 Watts more power than both of them!!  This reiterated to me the fact that my body position on the bike needed addressing.  At the time it was coming up to Ironman Switzerland so I was not prepared to start messing around with things so close to a big race.  What I did do was book a session in the F1 wind tunnel for the week after Ironman Switzerland with the team at drag2zero.

This proved to be a very very interesting day!
What I discovered was somewhat depressing and that is I generate a huge amount of drag relative to most cyclists 😦  Basically my bloody shoulders are like a massive set of parachutes!!  The guys at drag2zero were awesome and we spent ages playing around with things trying to find something that helped to bring those bloody drag numbers down.  After three hours in the tunnel we were out of time.  We had made a slight improvements in my position, saving about 10 watts but that was it. Having said that, I came away from the session having learnt a huge amount about the aerodynamics of my body in different positions and had a pretty good idea in my mind of what I needed to do to reduce those drag numbers.  Moving forward I have played around with these concepts and had some pretty positive results.
There is a mid week series of time trials held at Western on the Green.  It is not the fastest course in the world and I don’t think anyone has ever gone under 21mins for a 10mile TT on this course. However, it is around 4km per lap and makes it very easy to compare results assuming the wind conditions are similar.  Here are three results I have under similar wind conditions on this course comparing time vs power.

10 miles – 21:58 -> 398W  (old setup)

10 miles – 21:36 -> 380W  (new setup)

25mile – 54:10 -> 374W (new setup II)  => broken down this is 2 x 10mile in 21:40 & 5 miles in 10:50

Looking at the stats, after playing around with my setup, I am going very slightly faster and putting in 24 watts less effort!!!!
I am racing Challenge Copenhagen in just under 1 weeks time.  The bike section is virtually pancake flat, so a perfect course to put these adjustments in my bike setup to the test.  I know that on a flat course I can comfortably hold 300 Watts average for 4-5hrs and come off the bike with fresh legs.  In the Cotswold middle distance triathlon a few weeks before Ironman Switzerland I held 310 Watts average and clocked 4hrs 22mins for 112miles, coming off the bike feeling in great nick and running well.  Assuming I can replicate that in Copenhagen, hold 300-310 Watts for the 112 miles and stay in my new position on the bike, I could be going at a pace that previously would have required 324-334 Watts!!
This all sounds amazing in THEORY.  However, the poor result in Switzerland still weighs heavily in my mind.  How can I go from clocking a comfortable 4hrs 22mins for 112 miles one weekend to 5hrs 05mins and feeling spent two weeks later?  I have thought about this quite a bit!  The 4hr 22min ride was almost completely flat and pretty sheltered from the wind.  I was able to maintain a steady pace and don’t think I pushed over 340 Watts at any point in the ride.  In comparison the 112 miles in Switzerland were hilly.  The course climbed a total of about 1800m according to my garmin and I spent large segments of time (20-30 mins) at 370-380 Watts.  Added to that I was loosing lot of time with my granny like descending!!  After the first lap I was on for a 4hrs 50mins split which would have placed me at the front of the field.  Then my stomach issues kicked in.  I think this was mainly caused by my efforts at 370-380 Watts while trying to take on enough calories.  I have learnt that combination just does not work!!
So that is why I think things did not go my way in Switzerland.  If I am right, which Carli (my girl friend) will tell you is NOT that often, racing a flat course like the one in Challenge Copenhagen should allow me to hit a 4hr 40min bike split and still hit the run feeling fresh.  I still maintain that if I ‘get it right’ out there I should be able to run a 3hr 10mins marathon.  HOWEVER, I have been wrong so many times about what I think I can do and what my body is actually capable of!!  So while this should be possible in theory, I am not expecting things to work out.
With Kona just around the corner I am going to head out to Copenhagen with Carli.  Have an awesome weekend in Denmark, ENJOY the race and learn as much as possible from it about where my limits are!!
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Comments
  1. Tom Diethe says:

    Interesting reading … so 4:46 in the end and a 3:16 run … pretty damn close! Good effort 🙂

  2. Ian says:

    Hi

    How did it feel holding the new position for the 112 miles? Did you modify it for IM? Does not look like major changes, I have big shoulders and need to hide them too

    IP

    • Hi Ian,

      The new position is actually more comfortable than my old one. So had no problem holding it for the full 112miles. As you said they are not major changes, but as I learnt from my time in the wind tunnel. It only takes changes of a few cm’s to make 10-20 Watts savings. you just need to know where to make those adjustments. The thing is, what works for one person, might not work for the next. So unless you can afford to get into the wind tunnel is really is just guess work.

      All the best.

      Chris

  3. Richard says:

    Just jumped on your blog having followed your escapades on Sunday, awesome effort – that Wiltshire is a fish. Quick question…I’m considering using watts as a metric. What setup do you use in terms of power meters and how do ensure that you can both train and race using a power meter (thinking how people manage hub based power meters).

    • Hi Richard,

      I have been using a powertap in the hub for quite a while. It does mean that you have to have a ‘training’ wheel and a ‘race wheel’ but this system has worked well for me over the years. Hope that is of some help.

      All the best,

      Chris.

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