[V8] Goodyear Tires

[Buchholz, Steven]

... I was thinking that I should not have sent that earlier message ...
oh well ... guess that's what happens when I'm in a hurry ... 

I was pretty clear that I was talking about a 5kQ ... by definition that
means the car had a manually lockable open center diff.  No question,
with that car you could never lock the center diff ... but given that
you did not, the car ran just fine for a very long time ... after all,
what is a differential for?  I was just quoting that as an example of an
extreme situation.  

I guess what I was trying to get across is that I don't think its right
to come in with an unsubstantiated "understanding ... difference causes
stress on the drivetrain" either.  The AWD system has to be designed to
deal with a certain amount of difference in the diameters of the tires
at the corners ... so as long as you did a careful analysis of the
difference in the diameters of the wheels it might very well be possible
to have different profile tires on the same car and not risk damaging
the drivetrain.  Would I recommend doing it?  No, I've always used and
recommended having all four wheels be the same size with the same
profile tires ... to minimize the risk of dynamic (handling) issues.
The justification would have very little to do with risking the drive
train.  I have toyed with the idea of having different profile tires on
front and rear to change the handling characteristics, but never had
time to follow through.  

>From reading some of these responses I sense that some folks are not
100% clear on how Torsen differentials work ... Torsens are *not*
locking differentials ... they will and do allow differentiation.  Due
to the way they are designed, a Torsen diff will tend to pass more
torque to the output shaft that is turning more slowly.  I know that
I've heard of cars with Torsen center diffs having them be damaged from
towing long distances with one axle or the other stationary while the
other is turning ... I've wondered if the risk of damage is as much due
to the fact that the Torsen is working "backward" in those situations
... one output shaft is spinning while the other is stopped.  In any
case, remember that most V8s don't have center Torsens.

Steve B
San Jose, CA (USA)
> 
> I don't see how that could have lived very long at all.
> What kind of center diff did it have?
> If it was a torsen, it would have been trying to lock all the time
wouldn't
> it?
> If you had a electronic lockup, and it NEVER locked, it might work for
a while
> but I again would have guessed that the center diff eat itself up
quickly.
> The stresses on CV joints and the whole drivetrain would be
tremendous.
> 
> With the center diff locked, the drivetrain would have to explode in
short
> order. There has to be somewhere for all that stress to go.
> My experiences with more traditional 4WD trucks and Jeeps says that
the
> drivetrain binds up quick if there is any difference at all from front
to
> back.
> 
> Dave
> 
> 
> Quoting "Buchholz, Steven" <Steven.Buchholz at kla-tencor.com>:
> 
> > .. do you have any data that demonstrates what sort of increased
stress
> > is created on a drivetrain that has tires of different diameter?
I'm
> > sorry, but it does bother me to see this sort of statement without
any
> > data to substantiate it.
> >
> > Here is my data point ... I owned a 1987 5000 TQ which had the
proper
> > rear diff but the transmission from a non-turbo ... i.e. a final
drive
> > ratio of 4.11:1 in front and 3.89:1 in back.  I don't know how long
it
> > was in that configuration, but I do not expect that even this
magnitude
> > of a transgression did anything to the overall longevity of the
> > drivetrain ...
> >
> > The only things that I can think of to bear in mind ... the ABS
system
> > does tend to expect all four wheels rotating at the same speed ...
I'd
> > imagine that on the V8 the transmission controller might want to
lock
> > the center diff on an automatic when enough variation is seen ...
that
> > and the Torsen diff will tend to shift power away from the larger
> > diameter wheel.
> >
> > Steve B
> > San Jose, CA (USA)
> > >
> > > My understanding is that tires need to have the same circumference
in
> > 4
> > > wheel drive applications.  Changing circumference changes the
final
> > drive
> > > gear ratio. Tires should be *very* close to avoid strain on the
> > drivetrain.