Rolling resistance and AWD

[Andrew Duane USG/PE <duane@zk3.dec.com>]

Someone started something by saying:

> 0%, drivetrain frictional losses are balanced by the reduction in rolling 
> resistance because all four tires are recieving driving torque.

To which AudiDudi replied:

> Has anyone ever seen independent proof of this?  I know Audi makes the claim
> in all of their literature but I'm still just a teensy bit suspicious ... of
> course, most of the quattro cars have also been turbo'd and come with larger
> wheels/tires and shorter gears, which makes direct comparisons difficult.

And Kenny Gong opined:

> I thought rolling resistance is a function of the tire in contact with
> the road.  A rolling tire will deform at the contact patch, heat and
> sound radiates.  I do not see how when torgue is apply at the center of
> the wheel or at the contact patch (by the road) change the energy loss of
> a rolling tire.


Well, it just so happens I recently read a good article in Scientific
American on this very subject. The term is called "hysteresis", and is
a real factor in rolling resistance. The rolling resistance of a tire
goes up as (I think) the square of the speed, but as the fourth (!)
power of the torque being applied to the wheel. So, doubling the speed
makes a four-fold increase in drag, but doubling the drive-wheel count
cuts it by a factor of 16!


-- 

Andrew L. Duane (JOT-7)			duane@zk3.dec.com
Digital Equipment Corporation		(603)-881-1294
110 Spit Brook Road			http://www.zk3.dec.com/~duane
M/S ZKO3-3/U14
Nashua, NH    03062-2698

Only my cat shares my opinions, and she's pretty aerodynamic.