Well, that's not really a good test since there were so many variables that weren't controlled. The only way to measure the difference in wheel-performance is to at least maintain constant speed or constant power-output. And control all other variables like air-temp, wind-direction and speed, relative-humidity, as well as air-density (same course on different days will have different air-density due to varying atmospheric conditions). You
MAY be able to compensate for those variations if you measured all those conditions, but they weren't recorded. And the rider's fitness-level and recovery-state will be different on two different days as well. Way, way too many variables to narrow down the performance differences between two wheelsets.
Originally Posted by
Sluggo
Well, I'd like to answer the OP's question anyway since this is such an academic discussion. First, let's use the Kreuzotter site to calculate bicycle-speed given various aerodynamic positions and power-outputs:
http://kreuzotter.de/english/espeed.htm. I used the following changes from the default settings:
1. roadster
2. hands on drops
3. air-temp = 70F for STP
4. height above sea-level = 0ft for STP
5. blank out
watts box in lower-left
6. enter
31mph in speed box in lower-right
7. hit CALCULATE
And we get
565 watts required to push that bike at 31mph in the drops at sea-level. Al1943 is correct in that using steady 50kph is an unrealistic test-speed as most riders won't be able to output 565-watts for long. However, let's use that speed since that was one of the few instrumented tests with data we can use. And it may closely match the sprint of an average rider and he'd want to know how much faster he can beat his friends if he upgrade his wheels.
Let's use the
18-watt difference between the "slowest" Mavic R-sys wheel used in that test versus the "fastest" Zipp-808 and plug that difference into the model:
8. blank out
speed box in lower-right
9. enter
583 in the watts box, basically 565 generated watts + 18 "free" watts from "faster" wheels
10. hit CALCULATE
and we get an increase of
0.4mph to 31.4mph when upgrading to the "fastest" Zipp-808 wheels or
1.3%. Of course this is only from the Mavic R-sys wheels. Depending upon what wheels you originally had, your speed-increase will be more or less than this.