[s-cars] Was: Subject: Re: One bad tire on my Quattro (torsen) NOW: Running tires which may not be exactly the same size due to wear

[Paul Heneghan]

I'm inclined to agree with Calvin here.

I did a few rough calculations, and I reckon that a 4/32" difference in
tread between tyres (as mentioned in the Tire Rack article as the limit for
Audis) is equivalent to having tyres with identical wear, and going round a
continuous bend with a radius of 150m. That would correspond to a steering
wheel angle of 15 degrees, or about 10cm off horizontal.

I live in the Cotswold Hills in the UK, and there is only one straight road
in the vicinity (an old Roman road).  Everything else is full of bends, so I
wouldn't be surprised if the average steering wheel angle is of the order of
15 degrees.  I cannot believe that Audi's rally-derived transmission is
going to overheat and explode under this stress!  One of the main reasons
for buying a couple of S6s was because they are supposed to be good at this
kind of stuff.

I remember regularly driving my 1984 80 quattro (called a 4KCSQ in the US)
at some speed across some very bendy Welsh roads for about 100 miles with
the centre diff locked (as recommended in the owner's manual).  You could
really feel the transmission windup with the centre diff locked, but the
only thing I was conscious of was the huge improvement in handling, and the
vague feeling that I might be wearing the tyres a bit faster than normal.
That car did 185K miles before I had to sell it (my wife wouldn't get in it
anymore as she said it looked tatty - can you believe it?).  The
transmission was still the best bit of it.

I would hate to start up another great Tor$en debate, but I doubt that
Tor$en diffs are significantly more fragile than the old lockers.

Call me cynical, but I'm always suspicious of semi-technical articles from
vendors (like Tire Rack) identifying problems which can only be solved by
giving them lots of money!

Having said all that, I would still try and match tyres on each axle, but I
would NEVER have a tyre shaved unless I was on a racetrack, or attempting a
land speed record on an Autobahn.

Paul
1995 S6 Avant (his)
1996 S6 (hers)

-----Original Message-----
Message: 1
Date: Thu, 10 Apr 2008 07:05:53 -0600
From: Tom Winter <tom at freeskier.com>
Subject: [s-cars] Was: Subject: Re: One bad tire on my Quattro (torsen) NOW:
Running tires which may not be exactly the same size due to wear
>
>
>Dave Kase <davekase at pdqlocks.com> wrote
>http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=18
>
>OK, so call me stupid, but if you are rotating the 5th tire (spare) into
the
>mix it's highly unlikely that all of your tires will be the same size. For
>example. I rotate spare into the mix for the first time, removing one used
>tire. Spare is new, other tires are used = different tread depth and no
>bueno according to Tire Rack. Rotate tires again, and then the "spare"
>(which started out new) stays on, one "old" tire comes off, and the old
>"spare" gets put on. First spare is a different size as is the second
spare,
>too. But both are now being used as daily drivers.
>
>Hmmmm.....
>
>And then throw in slightly underinflated tires (yeah I know, but I don't
>check mine every day, sorry) and the different wear between front and back
>or if your alignment is slightly off and you have more wear on one tire. .
.
>
>I'm guessing I'm screwed, as it's highly unlikely that all my tires are the
>same. Close, yeah, but it sounds like not close enough. . .
>
>I'd better go spend some money at Tire Rack to make it all good again ;-)