quattro Digest, Vol 36, Issue 28

[Bluemaxww1 at aol.com]

The theory is this, and proven on Semi trucks and other large trucks such a  
Dumps, Haulers, etc.,  different diameter tires, such as one worn and one  new 
tire of the same size, cause the axles to rotate at different speeds.   This 
puts undo pressure on both sides of the diff.  This will  eventually cause the 
diff to fail.  Not urban legend.  The same will  happen in a car.
 
The report on the trucks was in a maintanence magazine for fleet  companies.  
Our Utility followed the advice, and the diff failure rate went  down 52%.  
Savings in the first year of replacing pairs, or in some cases,  quad tires, 
was close to 1M.  The rear tires not worn out enough were  simply used on the 
fronts as replacements.
 
Greg W.
 
In a message dated 10/9/2006 9:31:01 AM Pacific Standard Time,  
audi at humanspeakers.com writes:

The  locked diff probably wouldn't get hurt, it's the tires that get 
eaten if  they can't slip a bit.  Running different tires on an unlocked 
diff  can supposedly "wind up" the diff and kill it, though, according 
to, as  you say, the legend of the street.  This goes for 4wd trucks 
(etc.)  as well as quattros.

Anyone who actually knows what they are talking  about, feel free to add 
accurate details...

-- 
Huw  Powell