Frequently Asked Questions


It’s going to be a bit rider dependent but for me my Trek Madone with the original RaceLite wheels comes in at about 0.3600 with road kit and a road helmet. My basic TT bike / training bike with unbranded 50mm deep section wheels comes in at about 0.2100. That’s 0.1500 differential, or about 150 virtual Watts.
Some power is lost due to the TT position, because the hip angle is closed, roughly 10% of FTP, so 20 Watts in my case. So if I’m doing 20mph with an average power of 200 Watts on the road bike that translates into 23.6mph with an average power of 180 Watts on the basic TT bike.
It’s going to be a bit rider dependent but for me my Trek Madone with the original RaceLite wheels comes in at about 0.3600 with road kit and a road helmet. My Cervelo S3 with 303FC wheels, Aerotunda bars, TriRig aero brakes, more aero road helmet and hidden cables comes in at about 0.3000. That’s 0.0600 differential, or about 60 virtual Watts.
So if I’m doing 20mph with an average power of 200 Watts on the Madone that translates into 21.8mph with an average power of 200 Watts on the Cervelo S3.
It’s going to be a bit rider dependent but for me my basic TT bike / training bike with unbranded 50mm deep section wheels comes in at about 0.2100. My optimized TT bike is a Cervelo P3 with a Zipp Super 9 disk, a Zipp 808 NSW on the front, TriRig aero brakes, Ventus II base bar and Di2 with hidden cables and that comes in at about 0.1750, and that’s with the same skin suit and helmet, and with the same geometry for body position and ride height. That’s a 0.0350 differential, or about 35 virtual Watts.
So if I’m doing 25.96mph for a 23:07 10TT with an average power of 180 Watts on my optimized TT bike that would translates into 24.15mph on my basic TT bike and a time of 24:51.
I’ll test the basic TT set-up with the disk and the 808NSW at some point to see how much of the differential is down to the wheels. My guess is that it’s about 0.0160 for the front wheel and about 0.0100 for the disk, given my previous tests of wheels.
It’s going to be a bit rider dependent but for me my Trek Madone with the original RaceLite wheels comes in at about 0.3600 with road kit and a road helmet. My optimized TT bike is a Cervelo P3 with a Zipp Super 9 disk, a Zipp 808 NSW on the front, TriRig aero brakes, Ventus II base bar and Di2 with hidden cables and that comes in at about 0.1750.
So if I’m doing 20mph with an average power of 200 Watts on the Madone that translates into 26mph with an average power of 180 Watts on the Cervelo S3.
It’s probably never going to be as good as an optimized TT bike but it could be as good as a basic TT bike. Some events ban the use of disk wheels but something like an 808 NSW rear wheel (or the ENVE equivalent) is nearly as good as a Super 9. The easy equipment gain is from fitting aero wheels. You are always going to have the conventional drop handle bars and shifters out in the wind.
It’s not just a question of bolting on a pair of clip-ons. Getting your arms “in-board” is only the start. You then need to work on getting you torso into an aero position.
Yes. There are two sides to this, equipment and riding position, again wheels are the easiest place to make an aero gain with equipment investment. Body position and helmet choice are the other two key areas where gains can be made.
You need a benchmark to ensure consistency within a test session and continuity between test sessions. For a more complete explanation read our information note (downloadable pdf file).
Once you have found a suitable track / circuit / road to test on then aim to test in the same position with the same kit for about an hour. Try to keep the power application smooth and stay off the brakes unless you need to use them for safety. You can vary the pace but change pace gradually avoiding any power spikes if possible. The weather history is available “on the hour” so if you can run the test between two “o’clocks” then you’ll have weather data for the start and end of the test so that you can see if there were any significant changes in Crr and air density.
Yes, all you need to do is establish the CdA for it in the same way as you did initially, with an hour long test. Your first benchmark set-up and position is probably not going to be your most aero. You don’t want to have to keep switching back to an old set of wheels or a different skin suit every time you do a session to check your benchmark. At the end of our process your benchmark should be your most aero set-up. You will then truly be in the area of marginal gains.
When the temperature drops below about 10’C I start to use tight road kit with a base layer. This becomes my new benchmark. When the temperature gets down to around 4’C I start to use tight winter kit with a base layer and this becomes my new benchmark. The CdA will increase because of the different apparel, and there will be a bit more variability, as there will be some wrinkles in the clothing and they will never be in the same place every time. Testing in these conditions is more to do with training in the TT position but you can still get some useful data.
Ideally you want to test in conditions with a light wind or no wind. A light wind for aero testing purposes is anything up to about 7mph. You can get comparative results in a wind up to about 12mph if it is against and behind for the majority of your test route, or up and down the straights if you are using an open-air Velodrome. The banking shields you a bit on the corners. A cross-wind will increase the effective wind resistance and show up as an increased CdA. A wind that is gusting is a problem as it will introduce random variations. Testing in very windy conditions becomes an exercise in bike handling which is still a useful thing to do. Put a shallower front wheel in and look at the impact that this, and the wind, has on the CdA figure.
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