Re: Torsen bites Performance Car

[Sargent Schutt <sargent@novagate.com>]

David Gump wrote:
> 
> oh sh*t, i knew i shouldn't have said anything....
> 
> confused is as confused does...

>From the 'horse's mouth' department. :) 
> 
> my point was that scott says that the bite does happen in high cf conditions,
> ie. a torque shift at t*max* at 7/10ths driving.  in low cf conditions, as you
> have so accurately said, the locker can go from 0-100 torque and back to 100-0
> torque.  depending upon grip.  in the same conditons, the torsen can go from
> 28/72 to 72/28.  so, by your own argument, the locker is worse!

Yes, but you are only at Step 1 of the argument. Step 2 says the road surface
is variable and effectively unpredictable with respect to cf. Because the
torsen can be fooled by slip angles and wheel spin (w/o complete wheel lift),
torsen is also unpredictable. Note: by mechanical/physical definition, torsen
stands the risk of sending the torque to the wrong axle at the limits (b/c of
wheelspin/slip angle). When torsen is fooled, it may end up sending the torque
to the axle with less actual traction. 

The locker is predictable: when the center is locked, there is no chance that
the front axle will spin faster than the rear. You are at the mercy of the
road surface there, not the device. When torsen gets fooled, it creates a more
dire situation than the locker, as it applies as much as 78% of the torque to
the axle with the least traction. The locker can only send 50% of the torque
to the axle with the least traction, and since it is locked, you theoretically
(for KISS) have as much as 100% of the torque used by the axle with the most
traction. 

Mind you, torsen doesn't get fooled all the time, but it can and does happen. 
Usually only above 7/10's, which is terrible time for the car to become
unpredictable. Hence some of the comments on quattro handling at the limits.
>From what I've read in mags and seen here on the list, it appears to be much
more/(only?) a problem in the large type 44's and possibly the A8. Not so much
the case in the smaller cars (completely different chassis dynamics. Same
physics, but the equations produce differnt outcomes because the variables for
weight dist, overall weight, wheelsbase, etc are totally different)

In the torsen you have two unpredictable variables playing in tandem. Imagine
having RWD and experiencing an erratic throttle mid corner. That is what
torsen can do. To the extent that torsen does not get fooled, it is a nice
device. But, if the torsen center were accompanied by some sort of limited
slip front and a torsen rear, the torsen center would be able to make wiser
decisions. With open diffs, it can and has been repeatedly fooled. BTDT, not
my imagination. That is also why you don't see winning rally set-ups with
torsen centers and open F/R diffs. Read the C&D Subie article, for example.

> 
> my 70% torque with the torsen is in reference to one axle getting 0% torque
> reaction (ie. its on ice).  i didn't state this, i thought that this would be
> clear.
> 
> mmmm, which one of those is better?

Well, you made a better effort with the torsen v. locker rebuttle than the
following torque shift mistake. I'll let the latter slide, you'd have be a
real contortionist to wiggle out of that one. :)

c-ya!

Sarge