Quote:
Originally Posted by serialk11r
Rolling resistance is a constant value, good estimate is about 0.008 of the car's weight.
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Yeah at legal speeds rolling resistance ends up being close to 0.008 * weight, but according to that spreadsheet it starts increasing around 80 MPH and it's significant above 100 MPH.
Quote:
Originally Posted by old greg
For force, yes. For power, it scales linearly with speed.
Oh, and LRR prius tires FTW.  |
The formulas in the spreadsheets are:
fs = Speed Effect Coefficient
V = speed (mph)
Fd = force rolling drag (lbs)
fo = 0.008
W = weight (lbs)
fs = 0.00195 + 0.000024833 * (V - 150)
Fd = (fo + 3.24 * fs * (V/100)^2.5) * W
From what I've read, though the force required to offset rolling resistance isn't related to velocity, at high speed the additional heat increases the coefficient of friction. I got curious about the formula's numbers and the 5/2 exponent, so I clicked around the domain where the spreadsheet came from and found rolling drag at
http://www.mayfco.com/keith.htm
DR = W * (fo + 3.24 * fs * (V * (60/88)/100)2.5 (where 60/88 is just a conversion)
It's also mentioned at
http://www.physicsforums.com/archive.../t-321017.html
http://www.ffcars.com/forums/17-fact...top-speed.html
At some point I might dig my old textbooks out of the basement to look it up.
Anyway, while putting this together last night, it also occurred to me that the FT86's "Prius" tires ought to be advantageous for this. Everyone bashes them, but if steering feel is as good as the reviews say, then I think they make sense.