I was bored today and since I've just had an excellent tank mpg drop during the last 1/4 tank because of a cold spell I decided to play around with the temp drag relation.
All units used are metric, the only search I found was a chart with Imperial which meant very little to me.
Here's what I came up with.
drag equation
D=Cd*(1/2*p*v^2)*A
Then I used this link to find
past Canadian temperature pressure data for my area.
Then this calculator to calculate
air density.
So using my quick calculated values for my Optima estimated Cd .28 (stock is .29 hybrid has .26) and frontal area of 2.2m^2 I compared the drag at -4C and 101Kpa and 25C 99Kpa at both 90km/hr and 110km/hr.
I found that at 90km/hr:
-4C drag is 25.18N
25C drag is 22.27N
At 110km/hr:
-4C drag is 37.60N
25C drag is 33.20N
So in the winter time going the difference from 90-110km/hr creates about 2N more drag than in the summer. Of coarse there are all the other reasons why winter fuel economy sucks too but I found these numbers interesting. I also found that last night after power washing the ice cunks off my car my avg to work was about 12% better.
Also just for fun I plugged in the EV1 and VW XL1 Cds of .18 and that would mean about 14.32 N at 90km/hr and 25C or 35% better.
This really motivates me to improve my cars aero!