Charlie Baker Time Trial - 6-18-08

With Longsjo coming up in just another 2 weeks, tonight was one of the last Charlie Baker Time Trials I could use to prepare. Early in the season it was my intention to focus on time trialing and be really dialed in by now. That plan was set back when I crashed and totaled my Orbea back in late April. Instead of focusing on TT positions, I spent more time on dialing in my road position on the new Cannondale. Not until the past 2 weeks have I made any significant efforts to work on my position.

This week was a highly experimental week. The “cookie-cutter” position that I’ve been trying to make work just didn’t seem very fast. In fact, it was hardly any faster than the cannibal position with no aero bars. On the plus side it was comfortable and power output was good. I wanted to go the other direction with my position. I wanted to try a position that was aggressive and very aerodynamic, with no concern for comfort/power output.

Also experimental was the equipment. This was the first week I’ve used all the aero toys which include aero bars, aero helmet, disc wheel (covered open pro), carbon front wheel, skinsuit, and shoe covers.

I was well rested for the time trial, coming off of two recovery days. Weather was 67F and about 50% RH with scattered T-storms in the area. The rest would help my time, and the weather would be about average. Warmup was good including a one hour ride to the race followed by a few VO2 max efforts within 15 minutes of the start.

Excitement got the best of me and I started off too hard, 410W for the first minute, 374W for the first two minutes, well above threshold. Heart rate reached 185 bpm 2 minutes into the race. Threshold HR is about 175-180. I realized this early on and tried to settle into a more sustainable pace. I had a fast 30-second guy (with no aero gear) that may have contributed to my going out too hard.

The racer staged 30 seconds behind me caught and passed me in Carlisle center. I was dragging a bit going up the hill into town center so I imagine he made up a bunch of time on me there. On the downhill out of town I swear he practically stopped pedaling. I was pedaling as easy as 150W at times trying to avoid passing him back. I think this little break may have given me a taste of how nice it would feel to stop pedaling and it was all downhill from there on out.

As we turned onto Monument Road I was really getting sick of racing and my power output went way down, and my frustration way up. I couldn’t get comfortable in the saddle and it seemed like there was no efficient way to pedal. At one point I looked down and was doing only 180 watts. Fading power output left me with a good amount of energy for the finish and made a decent sprint effort to cross the line at 24:16.6 according to my PowerTap (although official time is always slower for some reason). This would be a PR of 43 seconds over my previous best which was set 2 weeks ago.

Average power for the race was a new low for the season, 252 watts. Average heart rate was 180 bpm, a new high, maybe due to good rest. Power decreased over the course of the race, likely due to a combination going out too hard and becoming uncomfortable in the aggressive position. Average power in 5 minute increments looked like this:

First 5-minute block: 323W
Second 5-minute block: 248W
Third 5-minute block: 232W
Fourth 5-minute block: 220W
Fifth 5-minute block: 231W

Seeing the average power dip below 230W for the last 15 minutes of the race was a big shock. On training rides in road bike position I’ve averaged 230W for literally 3 hours. I think shows just how uncomfortable the aggressive position was.

White Mountain Wheels (see link on right) has an Excel spreadsheet that makes for interesting time trial analysis. It requires a several inputs including rider weight, equipment weight, weather conditions, CdA (aerodynamic drag), rolling resistance, power output, and course details. I’ve been using this model to calculate the theoretical CdA of my various time trial positions. I download gps (.hst) files off of motionbased.com for each TT course I want to look at, simplify the courses up into 20 or less segments, and input that into the WMW model. Inputs such as weight and weather conditions are pretty easy to determine. Wind and rolling resistance are a little bit of a wag. Calculations aren’t very sensitive to variations in rolling resistance, although wind calculations are. Wind is probably the largest source of error in the model. For the CBTT, the course is run in a loop and is pretty well protected from wind compared to other courses. This does help minimize the error created by wind. Power output is also easy, I just use the power numbers from the PowerTap. Using this methodology I can somewhat accurately calculate my CdA for various positions. I think it’s better than just comparing power output and speed because it takes weather conditions (air density) into account.

As I said in the second paragraph, the goal for tonight was not to get the fastest time possible, but instead to get the best calculated CdA possible. Assuming that this was the goal, the night was a huge success! Here are the CdA numbers:

The April 17 time trial was a massive disappointment because I had much higher expectations for my first time using the aero bars. In the May 25 time trial I had taken almost a full 90 seconds of the April 17 time with out using any aero equipment! This was largely due to average power increasing from 258W to 285W, but I do think CdA was better in cannibal position than with aero bars. On June 15 I performed some serious testing, doing intervals on the CBTT course with aero gear, including helmet (I got lots of funny looks), and achieved a calculated CdA of only 0.300 (at nearly 300W). This was extremely frustrating. However, after making some aggressive adjustments, I am very pleased to see that my calculated CdA for the June 18 time trial was a whopping 0.230. This value is even better than the benchmark CdA set by White Mountain Wheels for full TT gear of 0.239. Granted power output is suffering severely, but I think this can be fixed by making some minor adjustments to improve comfort. I am very encouraged to finally have achieved what I think is a good aerodynamic position.