Anybody know how much we can upsize our tires on our 18inch rims?
What can we put on which will improve handling. Also what tires are the best for our cars?

 

Sometimes you can fit up to 335's on the back, probably 275's on the front, but some tires might rub so it's risky. I would say you are certainly safe with 315 rear and 265 front. Things you need to keep in mind is how much if any your car is lowered and how aggressive your alignment is. Both will determine if you have issues or not.

I would say Michelin PSS would be a good tire for your car.

 

OP is asking about stock rims. No way you're going to fit a 265 or 275 and 335 on 18x8/11 twists. 235/315 GT2 sizes is about it....

 

I run 295/35 /18 rears and 245/40/18 fronts on stock rims.

 

235 or 245 front depending on brand, and 315 rear with stock wheel width

 

There are some good tire options in 235/40R18 and 315/30R18 combos. Both of those should fit okay on stock rims (not too bulgy), and they should be very close to the same diameter front and rear (for those with AWD).
-Dan

 

Are you still AWD? I'd love to go with 245's to help out with understeer. Wouldn't 245/35 be a better choice though? Much closer in size to the rear tire in diameter.

 

are you sure the 245/35 would still work up front on an AWD car?

per tire calculators, it'd be 840 revs/mile as opposed to the ~818 for the GT2 sizes and the ~830 for the stock tire size. Not sure how sensitive the AWD system is, and the difference is only a fraction of a percent, so I gotta ask

I guess as the rears will wear out faster than the fronts, the revs/mile will gradually wear to become closer together with the 245/315 set up anyways..

 

HI,As I posted in the past years on many threads > I ran .5'' difference between front and rears for 25,000+ miles, numerous dyno runs[AWD],long road trips and numerous 160+ runs without any problems..
You really have to measure the diameter of any tire on the rim because sometimes those specs are wrong AND the width of the rim other then the info/spec rim size changes the diameter..Been there done that..