Yesterday I went out to do a personal 8 mile TT on my road bike (essentially a 20 minute or so interval) in the cold for us weather (44 F). I noticed a significant decrease in speed speed versus doing the same kind of ride in the heat of summer. At first I thought that I might have lost a bit of FTP as I have lost a significant amount of weight, but the Kreuzotter calculator gave me very comparable power numbers between the two types of rides I'm guessing that the increased air density (and hence drag force) made the difference. Any of you TT guys with power meters have good data on how air temperature changes your times? Is it only changes in drag? Is there any benefit to the increased concentration of oxygen due to being cold like with IC engines, i.e. more oxygen intake per breath?