Perry-Roubaix TT Analysis

The last post covered the bad and the ugly from Perry, so now I'll allow a little space for the good. I had a good TT in Perry and took 2nd. I've been working hard on my position on the bike, I upgraded some equipment, and I've made it a point to do at least one hard ride per week on the TT bike. It's paid off. I'm faster now in TTs than I was last year. This weekend my average speed was 25.9 mph for about 10 miles.

In July 2007, my coast-down testing showed me having a CdA = 0.265 with an assumed 0.005 Crr (rolling resistance coefficient). Last week, after lots of tinkering with my position, adding a rear disc wheel, and installing Veloflex Record tubular tires, I reduced my assumed Crr to 0.045, which - if all else was equal - should have resulted in a higher CdA measurement. But I found that my CdA had dropped consierably to CdA=0.233.

To put that in perspective, a drop in CdA from 0.265 to 0.233 would result in a savings of 56 seconds on a pan-flat 10-mile TT course holding a constant 300 watts.

Using a very rough approximation of the segment lengths and slopes encountered in Perry this weekend, I modeled my ride with known CdA, distance, and time to calculate wattage. I normally put out more wattage while climbing, so that was considered for each segment. The model shows that my average power was about 299 watts. If I'm putting out about the same wattage now on my TT bike as on my road bike, and if my 60-min power is about 95% of my 20-min power, then that relates to a FTP of 299 x 0.95 = 284 watts, which is exactly what I recently tested it to be.

Here's a snapshot of the model. You can find the spreadsheet at Badger 3 if you'd like to use it.