procainestart
procainestart HalfDork
12/16/08 2:57 p.m.

When you let off the throttle while driving an AWD car with a center diff that transfers power only when the front wheels slip, I assume there would be no compression braking forces to the rear once you lift, right?

What about on contemporary computer-controlled AWD systems: do they transfer compression braking forces through the center diff, too?

My sense is that the manufacturer would not want compression braking forces acting on the rear wheels because if, in slippery conditions, the driver lifted on a corner and the rears were slowed somewhat, then the car might be more prone to oversteering. Or not??

So how's it all work these days?

Thx...

fiat22turbo
fiat22turbo GRM+ Memberand SuperDork
12/16/08 3:11 p.m.

Damn, that is a good question. I believe it somewhat depends on the type of transmission involved along with the type of differentials.

Many automatics tend to freewheel on deceleration (which is why people tend to tap the damned brakes all the time!)

I would think many of the center diffs would decelerate all 4 wheels, but then again it would depend on the type of center differential involved.

Strizzo
Strizzo Dork
12/16/08 4:02 p.m.

i remember reading a bit of advice given to a magazine writer that was driving a porsche 911 turbo (awd) on the salt flats or some other high speed event, and they told him not to lift if anything happens because that would transition the car from an awd car on-throttle to a rear engine, rwd car with trailing throttle. which on loose surface might mean it tries to loop at 190mph

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