[A4] Replacing a Partly Worn Tire?

[thejimrose]

lol.. your driveline wasn't built by nasa. there's a considerable
amount of slop in the system to compensate for the irregularities of
the real world. one mismatched tire, even grossly so, won't hurt
anything because the car has open front and rear differentials. open
diffs are very forgiving of tire diameter differences [since every
time you are in a curve the tires are moving at different rates]. the
center diff less so but still...

it is best to try to get the same brand / model / size - so that
traction, load rating, etc are all as close as possible.  note that
manufactures lie like crazy wrt tire size ratings. can't tell you how
many times i saw 1 oe's 245 be the same size as someone else's 265.
you can usually get the actual tire dim's from the manufacturer, handy
for buying tires that are actually the same size vs the same rated
size [i believe they're allowed up to a 15% deviation in actual dims
from stated sidewall size]. otherwise just measure overall diameter
and get the closest one.

to illustrate, i have a mismatched set of snow tires for my a4.
they're all 225/50/16 but the pirelli's are about 3/8" taller than the
dunlops. if i put the pairs front to back, the center diff binds on
the highway [steady state so 50/50 split]. if i put them side to side,
no issues at all.

maybe tmi, but hth..
jim