One Flat Turns to Four

[Joshua Van Tol]

On Wed, May 2, 2012 at 11:31 PM, Huw Powell <audi at humanspeakers.com> wrote:

> Enough of the silly armchair engineering.  The reality is that mismatched
> tires will tear a differential apart.  This is because the light spider
> gears are transferring power all the time.
>
> Pickup truck people find this out when they run totally different wheels
> and tires front and rear in 4wd.
>
> But that's because pickup trucks don't have a center differential, at
least not most of them. They have a transfer case, which simply drives the
rear drive shaft at the same speed as the front. Similar to driving around
in a quattro with the center diff locked. The spider gears aren't exactly
"light" btw. The bearing surfaces arguably aren't designed to take
continuous high speed rotation, but the gears themselves are pretty sturdy.


> The amount of wear on a given tire is probably not enough to worry about,
> although regular rotation is encouraged, and Quattros should get four new
> tires at a time.
>
> Putting on a new tire of same brand and model with three half-worn ones
> might be ok.  Wrecked tires are the nightmare of quattro systems - how much
> difference is ok?
>
> Anyone ever hear of a Q diff blowing up (under 500 hp)?  Ever?
>

Yep, happened to someone on Motorgeek. The pin that the spiders ride on
worked itself loose and gouged a huge hole in the side of the tranny case.
Instant stop. I'm pretty sure that was at higher power levels, but not 500
hp.


>
> My comment about shaving the new tire was a joke.  A well meant joke.
>
> - Huw
>
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