[A4] tire sizes

[thejimrose]

hey guys, just have to bring a little common sense to the party. different
tire sizes would cause the wheels to rotate at different speeds, right?
which also happens when?

every time you turn the steering wheel. and the inside wheels are travelling
slower than the outside wheels. that's why the diffs are open not locked. if
minor deviations in rolling diameter were an issue, the diffs wouldn't last
very long at all.

besides - it's not a "perfect" world. recalling werner and his fabulously
principles of uncertainty; no 2 sides of the road, no 2 tires, no 2 diffs,
no 2 mating surfaces, etc etc etc are perfect so there is always going to be
some 'slop' in the system. audi knows this, and while sure, it's a good idea
to keep tire sizes as similar as possible, the difference between 2 same
sized tires with different wear is SO tiny it's just not going to have any
meaningful effect. it would be the same as running 1 tire a few psi low. not
"ideal" but not going to break anything.

that said, if the other tire is close to the end of it's life, sure get a
new pair of tires since you'' be at the shop anyway. but if it's got more
than 30% life left  i'd just get 1 new tire and be done with it. im sure the
audi guys factored in some % deviation in tire diameter in the differentials
to account for spare tires, odd tires, different tire pressures and the rest
of the 'slop' in the system. if they hadn't there would be a trail of broken
audi diffs littering the roadways.

and i've NEVER heard of an audi diff breaking. it's about the only part that
doesn't break.