So this past weekend I participated in a stage race that started with an 8.6 mi TT. I opted to use my Canyon Aeroad with Enve 5.6 disc wheels over a borrowed TT bike due to concerns with handling and generally being unfamiliar with a TT bike.
I averaged 300W over the duration of the out-and-back course for a time of 20:01. Interestingly a friend of mine with full TT rig and aero helmet held the same average power and his time was only 11s faster. He is a shorter individual and a sprinter with big calves. So I put my information in Best Bike Split and had to adjust CdA to 0.306 in order to get the estimated time to 20:01.
My understanding is 0.306 is a pretty low CdA on a road bike so I question how much of an advantage I would potentially get with going to a TT bike with similar wheels and helmet. If I assume 1.5 mph faster on a TT bike, my time would have been 18:58 with a theoretical CdA (via BBS) 0.255. 2 mph faster would yield a time of 18:37 and a CdA of 0.242.
I guess a few questions/observations are whether or not I held a good position on the road bike to compensate or perhaps my friend had a bad position on his TT bike and whether or not I would benefit greatly by getting a full TT bike (aero extentions out due to H11 cockpit). I’ve also heard of low CdA values in the 0.20-0.22 range so maybe there’s even a greater benefit?