Hi guys, so car I just bought has aftermarket 21” wheels with front 255/30 (stock is 245/35-20) Toyo proxes tires and it’s also lowered with H&r springs. The ppi found one tire worn and car out of alignment. So I for sure will replace with Michelin p4s but was wondering what size to go with. I’m keeping the 21 wheels for now but wonder if 245/30r 21would be better as far as alignment and drivability, only thing holding me back is you lose a little sidewall vs 255/30r21 and car is already riding pretty stiff. Any insight would be greatly appreciated
Thanks.

 

Your goal should be to match the stock tire diameter to maintain stock speedometer accuracy, wheel well/suspension clearance and gearing. If stock is 245/35-20, your wheels are 35.4 inches in diameter (not accounting for flattening on the road), you want a tire within about 5% of the same diameter. Wider tires can start to rub on the wheel well liner, fender or suspension parts. You need to make sure there's clearance (10mm is probably fine). You also need to be mindful that for every wheel width, there's an acceptable range of tire widths. Too wide or narrow of a tire and there may be safety concerns.

 

Yes both tires are very close to stock size as far as diameter, .7%. The 255 tire is wider by about 4% but also has .1 more sidewall. Neither will rub.

 

I like narrower tires, less tramlining and better feel. But most people go for wider tires for grip.

 

Yeah me too, but narrower tire has 3.4% less sidewall and that’s where my indecision comes in, car rides very stiff already.

 

So 255/30 r21 installed and holy crap what a difference. The car has zero tram lining and is much quieter and smoother. I think stock size is way to go, if it improves my upsized tired car this much it must be even better on stock wheels.