[torsen] Re: [urq] RE: Quattro handling

QSHIPQ at aol.com QSHIPQ at aol.com
Wed Apr 17 09:11:46 EDT 2002

All reading and theory aside Dave, what we find DRIVING them is that ALL 
torsen OR lockers change torque allocation constantly.  The torsen LOOKS to 
return to 50/50 all the time, but it's never always there.  Neither is the 
locker.  The only one that constantly gives 50f/50r is the open.  We can 
agree on that much.

I completely understand WHAT you are saying, what we should do is look at the 
experiences in HANDLING of either differential in terms of the constant 
torque shift.  I cringe a bit at any comparo of the torsen to a locker, in 
handling OR design.  What is found is that in a constant cf condition, in U 
breakaway at the limit of adhesion.  This is due to the front weight biased/ 
powered/ steering wheels > physical properties of awd car handling that 
allows no speed differention between f/r axles.  This *could* be the case in 
a torsen, but if turning radius causes torque allocation, on power up, at the 
limit of adhesion on the same cf, the rears could break away first, OR the 
fronts could break away first.  Which is it?  Well, there are many factors 
that will dictate that, including where the torque is AT the time of the 
break.  Again, constant cf.  We *might* stretch and see 
similarities/advantages of 2 wheels on 1 cf, two on another, but that lasts 
the length of the wheelbase.  IF your proposal is that 4 wheels ALWAYS have a 
differing cf all the time, I might agree in theory, but in practice and 
methodology of testing and modelling, those differences appear to be small 
enough to not effect predictable results or white papers (even to the 
engineers of the torsen).

With regard to the "driveshaft" sturdiness you mention below, Audi actually 
mentions the fact that the driveshafts are designed to handle 100% of the 
torque applied to them.  IMO/E Driveshafts have *never* been a factor, even 
adding and ADDITIONAL 100% of engine torque TO the equation, so not sure the 
point.  I guess what jeff might be pointing his finger at is the eclipse 
turbo cars that manage to snap driveshafts quite regularly.  I'd love to meet 
the urq owner with that experience, I haven't even seen it in the rally cars 
(and my inspections of many would conclude they use production driveshaft 
assemblies).  I've read several audisport rally books in the last year, I 
can't recall a *SINGLE* failure do to a torque applied snapped axle, can you? 
 Most "torque" related failures of the A1/2/SQ/S1 cars were the front diff 
ring gear.

The "behavior" in locked center diff cars has plenty of btdt on this list, 
and in rally, and in race, even today.  Even Istook runs locked center in his 
S4tt.  *Best*?  I make no claims of that, only that predictability comes up 
routinely in ANY interview with audi race car drivers using the locked center 
diff.  I haven't found that word mentioned in the context of "torsen", in 
fact...  (telemetry signal interupton:)

Scott Justusson

In a message dated 4/16/02 10:43:53 PM Central Daylight Time, 
deaton at tranzrail.co.nz writes:

the other obvious effect of this 0:100% factor of a locker, is that you have
to engineer the drivetrain so that any particular wheel can cope with 50% of
the engine's torque, whereas with an open diff, this is 25%.  with the rear
locker as a factor, the rear driveline has to be prepared to cope with 100%
of engine torque.  that involves weight and expense.

there is a detailed explanation of these factors in jeff daniel's book that
i mentioned earlier.

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