[torsen] "Correcting" understeer

QSHIPQ at aol.com QSHIPQ at aol.com
Thu Jan 18 10:26:02 EST 2001

Re: RSR article:

Let's get the quote exactly right:  "... the strong understeer went away".  
That really doesn't mean oversteer, only less understeer, or at best 
"neutral" which by definition (without shifting actual weight) is understeer. 
 Since you aren't changing the static dynamic of f/r balance, U can only be 
reduced.  I'd sure like to see a long term test update of that machine.  A 
quick calculation of the difference in f/r rotation shows 4% based on these 
numbers.  A couple of folks have mixed 3.89 with 4.11 on their lockers, and 
found *that* 5.4% difference to cause the car to lockup.

So, in a torsen machine, what Meyer has done is to bias the torsen itself 
*forward*, not backward.  When the car is in a straight line on dry pavement, 
the torsen is settled at 50f/50 rear.  With the tire mods that becomes 
54f/46r static torque bias.  This would indicate a car with more understeer, 
not less.  However, the common thinking of awd (including the latest S4) is 
that to reduce understeer, you bias the torsen forward as close as possible 
to the static weight.  That can be done with the torsen unit itself, or with 
tire sizing.  Doing it with tire sizing can affect the reverse torque 
(braking) allocation however, something I'd approach with some caution, since 
this can affect abs algorithums.  

Also, one would need to address heat problems associated with preloading the 
torsen with no other mods but tires.  

All that said, I drove Graydon's 5ktq (diffs open) with larger wheel/tires 
front, smaller rear.  A great improvement in handling on the 44 chassis car.  
I'm not going so far as to say oversteer, but understeer was reduced greatly, 
and turn-in improvement was impressive.

Interesting too, the MTM article points at the *smaller* rear roll bar than 
the RS2 with a stiffer rear suspension, helping lift throttle antics.

Interesting that Herr Meyer found the answer to reducing U, and audi followed 
suit, albeit 5 years later.  Sounds like a trend.  Here's hoping that trend 
doesn't include those god ugly borbet 'O's...

My .02

Scott Justusson

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