A trip to the local wind tunnel
Sunday morning. Once again I'm up before the crack of dawn suiting up in full timetrial kit and readying my TT bike as carefully as if this were the biggest race of the year. The objective isn't a big race though. For me it's something every bit as important. I'm prepping for another aerodynamic drag testing session.
The location is the local "wind tunnel", Centaur Road. It's about a kilometer long and just about as flat as a road can be. Even better, as you can see from the photo, it's almost completely surrounded, top and sides, by thick foliage. Centaur's about as close as you can get to an enclosed tunnel. Only the ends are open to let in the wind. And early in the morning before the sun comes up there isn't much wind this time of year.
Full credit goes to Andy Coggan for figuring out what an ideal location this is for using the regression method to determine CdA and Crr. Those are critical terms for understanding how fast you can go on a bicycle. CdA tells you something about how hard it is to push your way through the air as you ride. Crr is a factor that describes how easily your tires roll along the road surface.
How does it work? It's pretty simple, really. You ride through the tunnel a number of times at varying speeds, while holding position constant. It takes a few minutes' time to collect the data from your bicycle power meter file, but as quickly as you can plug the numbers into an excel spreadsheet you get a pretty good estimate of CdA and Crr.
Not only is this a fun exercise for anyone like me who enjoys a little applied math and science; but it's a good workout too. With all the various runs at different wattages, plus the extra TT intervals we did, I stacked up enough TSS points to call it an honest workout. Now, I'm not really sure what, exactly, this kind of workout really trains, but it's training all the same.
Ok that's pretty interesting!
Will there be a follow-up with results and conclusions, :)
No question about it, there
No question about it, there will be follow ups to this one. It's the conclusions I'm not so sure about.
I'm pretty sure I heard Andy right the other day saying he'd been working on optimizing aerodynamic position for 20 years or more. He's not finished experimenting by any means. Conclusions, it seems, are at the end of a very long path.
Stay tuned.
Conclusion
Lower is faster...unless it's not. ;-)
Seriously, as Mark mentioned optimizing your aero position is an iterative process, and one which never really ends because equipment, rules, and even your body tend to change over time. Field testing using a powermeter can be helpful, but so too are plain ol' eyeball fitting, evaluation of actual TT performances, and wind tunnel testing. I've been doing all four since the mid 1990s, but still haven't found a "perfect" position that would cause me to cease experimenting in search of more speed.
Solution? LOL
This is a never ending story if there ever was one!
Let us see, there is Power vs. time curves, that are shifted by external factors that are uncontrollable (such as Temperature/humidity). Further there is Power vs. Position. So this brings us to Power vs. Position vs. Time. Oh yeah, and our physiology is not exactly a stationary target (know that I am not as flexible as I once was). Lets not forget technology changes (ideally they are advances) and changes in rules...
Oh yeah, and the whole cadence shift that many people display in windy conditions...particularly those who ride a fixed gear;)
Post new comment