Saturday, September 6, 2008

VeloVets 10k TT - 14:02 (again)

Very nice day. Very little wind... Just enough to notice that the trip back was about 4km slower on average than the trip out... Averaged 45 out and 41 back... To arrive in exactly the same time as last time out a month ago... when there was a lot of wind and I did 48 out and 39 back.

Pavg was higher this time, 350 vs 332. Which doesn't make sense... 

Different skin suit? This was the older full length Cervelo skinsuit which has a different weave than the newer short sleeve VeloVet skinsuit I used last time.  Wouldn't think it would make that much difference. 

Bill Riley was slightly slower today compared to last month. 14:33 vs 14:20... 

Grasping at straws I checked the difference in air density.. Aug 6th, was warmer and lower air pressure (21.5C,101.41kPa, Dew Point 14.3) compared to doay (14.2, 102.07kPa, Dew Point 11.4).  Punching those numbers through a spreadsheet gives air density of 1.187 and 1.22 respectively... 

Then pushing those numbers through analytic cycling shows a nominal speed difference of about .4 km/h which is about 10 seconds... Or about  a about a 10 watt difference required to average the same speed (43kmh) for the two different air densities. So it would appear to make sense. I did work harder today... but it WAS harder just to get the same speed.

These also compare reasonably well with last years best time... 13:48. Which was on a day like last month (1.191) with power higher than today. But with an less aero bike position.