[A4] tires, speaking of tires, anyone have any used 17's lay'n around?

[Huw Powell]

>>Yes, but forcing a differential to constantly rotate to make up for tire 
>>diamter issues is hard on it.
> 
> It's a matter of degree.  As I said, you will almost never have exactly
> identical rolling radius on the different tires.

Correct.  What you want to do is minimize the amount of power the pinion 
gears have to handle.

>  The difference between a
> brand new tread and one that's at the wear bars is around 7mm on these
> types of cars.  That's just over a quarter of an inch.

That's time to replace the worn tire.

>  Brand new tires
> inflated to exactly the same pressure will be close.

They sure will.

>  But, the fronts wear faster than the backs. 

That's why we rotate tires.

> Oh, and don't ever park your car so that one side
> of it is in the sun, that'll cause the pressure on that side to be much
> larger than on the shaded size.

Oh man, what if I have to drive four hours with the sun on one side of 
the car?  Too bad I can't measure this out of curiosity for a few 
months.  Can someone in Oz (or anywhere sunny these days) test this?

> How far do you really want to take it?

To the cage, dude, to the cage... hehe

> Yeah, it's your car, you can worry about these things all you want.  Me,
> personally, I'll go with Audi's recommendation, and that replacing a flat
> tire for a nearly identical new one is fine.  I wouldn't put a different
> size on different wheels, but a new versus a used tire is almost certainly
> fine.  It sure was in my experience.

I would hope and try to get the same brand/model tire, but I know that 
is not always practical for people.  I'd be tempted to get two new tires 
and have a nice full-size spare for the next time I need it.

>>To take care of your diffs, they should at least be the same size.
> 
> Absolutely, if we're talking about putting a 55 series tire on a car with
> 60s on the other 3 corners, I totally agree that that's stupid.  But if
> we're talking about putting a new 55 on a car with 3 others with 25k miles
> on them, I would do it without worry.

I once saw a 4wd truck with bigger tires on the rear.  And a broken 
transfer case.  Of course we're not talking that extreme here.

-- 
Huw Powell

http://www.humanspeakers.com/audi

http://www.humanthoughts.org/