Sunday, October 28, 2007

Williams 30 vs. Mavic ES Preformance Report

Hi Athletes,

We just received this unsolicited report from one of the Webcor /Alto Velo Elite Cyclists.

We might be on to something here at Williams Wheels!

Report by:
Dominic Giampaolo
Webcor / Alto Velo Elite cycling Team
I've seen web pages that claim the rolling resistance of good tirescan save you 20-40 watts of power at the same speed. I've alwaysdoubted those claims would hold up in the real world. This pastSunday morning I decided to do a simple experiment to see how much ofa difference good tires and race wheels make over my normal trainingwheels.To keep the experiment simple I compared my training wheels againstmy race wheels.

My training wheels are:
Mavic Ksyrium ES
front Conti GP 4000,
rear Specialized S-Works Mondo(both with Mr. Tuffy tire liners)

My racing wheels are:
William's 30's (the new ones with ceramic bearings)
Michelin ProRace 2

Since I switched out the complete wheels instead of just the tires,this isn't just a rolling resistance test although that's certainly afactor. I also figured that switching the entire wheelset wouldmaximize the difference between the wheels making it easier to measureif there is a significant change in the power needed to pedal thebike.I started with the training wheels. I pumped them up to thestandard pressure I use. This registers 140psi on my pump, but Isuspect that the gauge isn't accurate. Anyway that's the pressure Inormally run so that's what I pumped them up to. I calibrated thecircumference of my wheels by getting fully suited up (includinghelmet, water bottle, etc), sitting on my bike and rolling out onerevolution of the front wheel. Then I set my SRM to that value(2107mm) and calibrated the SRM cranks. After I finished the firstset of runs I switched to my race wheels, pumped them to the samepressure, measured the circumference (2114mm), updated the SRM andthen double checked the SRM crank calibration which had not changed.The test course I used is a 1 mile loop over by the Google buildingsand the Shoreline theaters (Charleston, right on Joaquin, right onPlymouth (by the theaters) and right on Alta, which goes back toCharleston. It's dead flat (+/- 2 feet elevation). It was cool thatmorning (53 degrees on the SRM) and there was no wind.

For the test I decided to do 3 laps at 200w, 3 laps at 250w and 2laps at 300w on each set of wheels. That's about 10 minutes at 200w,just under 9min at 250w and just over 5min at 300w. I wanted to makethe runs long enough to eliminate small variances in how I tookcorners etc. I figured that by fixing the distance and power I shouldsee differences in the time to complete the laps and the measuredspeed. If it's not clear, I did take a break between the runs so thatI always started them from the same location. The 200w runs beganfrom a standing start, the other two I did from a rolling start overthe same start location (a spray painted line on the road). On allruns I tried to stay in the same position (on the hoods), did not usemy brakes and tried to follow the same line as much as possible.

I came pretty close on the power: on the training wheels I had 199w,249w, and 295w and on the race wheels I had 199w, 250w and 293w. The distance for the runs was also pretty close: 3.167, 3.162, 2.115 mileson the training wheels and 3.177, 3.157 and 2.130 miles on the racewheels (that's +0.3%, -0.2% and +0.7% difference).

To calculate the difference, I looked at the time to complete thelaps and scaled it by the difference in distance covered. The formulain the spreadsheet is more complicated than it needs to be but itworks out to be this:

(Race Distance / Race Time) / (Training Distance / Training Time)

The results of using that formula show that there is a noticeabledifference between the race wheels and the training wheels at allpower levels. The time to complete the laps was consistently faster at all three power outputs. Expressed as a percentage, the resultsare:

Power : % faster for race wheels
200w : 4.13%
250w : 3.69%
300w : 4.14%

In practice what is a 4% difference? Well at 300w it would requirejust over 12w more power on the training wheels to keep the samespeed. For me on flat ground 300w is pretty close to threshold powerand a 12w difference would push me over the edge much more quickly.In terms of time, if you were doing a 1 hour TT effort, the racewheels would save you 2 minutes and 22 seconds. As you can imagine,I highly recommend Williams Wheels!

Clearly good tires and wheels will save you a lot of energy in aroad race. In the past I've raced on wire-bead tires with Mr. Tuffy'sin them and poo-poo'ed the notion of nice tires. No more. This isthe kind of difference that equates to being able to win a raceinstead of being just ever so slightly more tired and not having thelegs to contest the finish.

Dominic Giampaolo