BulldogAE said:
I do understand that the Cd of something like a helmet does change, but most peoples heads are not too differently shaped. Also people always give drag coefficients in CdA. Because something like a helmet design has a fixed A there is nothing you can do about that. Having a power meter would be great, and I could figure out everything I need to know based on that, but just an average power meter cost nearly as much as my bike. I am just trying to figure out for myself something like how much an aero helmet helps compared to a regular or even how much regular helmets vary. I wish I could care more about bike aerodynamics, but I doubt that will happen soon. I would still like to know how different tri bikes and road bikes compare though, just for kicks.
Equipment will help you to mitigate overall drag BUT your position on the bike will possibly have as great-or-greater of an impact until you actually optimize your frontal displacement ...
Several years ago, I did a comparison based on simply moving my hands from the hoods to the crook in the drops where I reckon the actual change in my body 'height' didn't change by more than 2" since the difference in positions is more for hand relief ... if the difference is actually more-or-less, then it's whatever it is.
At altitude (6000+ feet) on a False Flat where the coasting speed was greater than 12 MPH, the difference in speed was about 2+ MPH for the different hand positions (and, subsequent change in body position).
On a steeper descent where the coasting speed was greater than 30 MPH (actually, closer to 35 MPH), the difference was approximately the same (i.e., 2.n MPH).
At-or-closer to Sea Level, the difference in coasting speed would probably be greater for the two positions as the speed of the rider increased ...
In other words, you could be wearing all of the latest-and-greatest aero gear + be riding on a TdF level TT bike, but if you were sitting taller than someone else who is more aero on his/her bike, then you might nonetheless need to expend more watts to maintain a given MPH.
I reckon that Lance Armstrong's less-than-ideal TT position (
i.e., Armstrong's slightly 'hunched' back appears to raise his frontal displacement by at least 2" more than it would be if he could 'flatten' his back the way other top tier riders do) finally caught up with him at last year's TdF -- undoubtedly, that is one reason why he spent a portion of this past year working toward improving his aero positioning.
Presumably, diminutive Leipheimer (who has a pretty good aero position) can go incrementally faster for a given wattage output than someone whose frontal displacement is greater.
So, as a suggestion, if the stem on your Road bike is currently barely lower than your saddle, then you probably want to set it so that it is at least 4" lower than the top of the saddle to help you acclimate to a more aero position ... then, when that is a comfortable riding position, get a TT bike where your back position is as close to flat as you can manage ...
That's a very circuitous way of vaguely inferring that some aero gear will undoubtedly help an individual to reduce their frontal displacement (you know, a skin suit is better than wearing a blousey T-shirt) & drag, but if they are not riding in an aero position then the benefit may be smaller than for someone else.
Hope that helps a bit.
