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      08-20-2008, 09:40 PM   #84
Lieutenant Colonel

Drives: Legacy GT - 13.704@99.39
Join Date: Jul 2007
Location: Manheim, PA

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Originally Posted by swamp2 View Post
I'm won't comment on the relative losses comparing Quattro vs. BMW except that the 100% rear bias available on the BMW does help substantially.
From previous information (and T Bones' recent post), it seems to me that the bimmer awd is a more sophisticated unit than the classic Audi. Not sure about how substantial the actual performance difference would be, however, since Audi has said for over 20 years that a driven tire exhibits less rolling resistance than one which is just along for the ride. The "not sure" piece is simple ignorance on my part, as I expect that all the info almost anyone would need resides somewhere in the SAE archives. I just don't feel like doing the research to run them down, and then paying for the pertinent articles.

Originally Posted by swamp2 View Post
I think the point is that regardless of the design or manufacturer AWD systems produce a significant amount of loss. If you believe the particular dyno numbers in the OP the RS4 losses are 18% vs. 12% for the M3. This difference is consistent with numbers used in simulation (numbers thanks to you, with my tweaks) of 3% for axles and 1% for a diff (12+2x3+1 = 19). No matter how you slice it 6% is a lot and for cars in this power range it is ~ 25 hp. In lb, at 9 lb/hp, this is ~ 225 lb.
Agreed. This plus the weight differential is what makes the M3 out-accelerate the Audi over any meaningful distance - meaning the M3 inexorably reels in the Audi after the banzai launch the RS4 is capable of, and keeps going.