In need of tire to wheel sizing input......

[Car Guy]

My mother's `06 Infiniti M35x needs tires before the snow flies and I need input before 'pulling the trigger' on a new set. The factory wheels are 18 x 8" with 245/45 tires but those wheels are gone and not coming back. A set of 18 x 7.5" wheels are currently installed (very long story) and will get the new tires. The only aspect of the new tire size I am hung up on is the width in relation to the smaller wheel width. The two sizes I am considering are 225/50-18 and 235/50-18. A 235 tire is ideal for everyday driving on a 7.5" wide wheel but the selection in 235/50-18 is not the best. A lesser but valid concern is the 235/50-18 size is near the high end of the factory diameter range. The diameter will work but I prefer to stay as close to the factory diameter as possible. The 225/50-18 size is very close to the factory diameter and the selection is much better. However, I am concerned the 225 width on a 7.5" wheel will be too thin ON THIS SPECIFIC VEHICLE. I do not want any issues in the future after spending ~$800 on new tires. My main concern is irregular tire wear but also handling, braking, ride quality, etc. My OCD will not allow me to just say "those will be fine" without doing adequate
research.....:goof


Any input is much appreciated! :thumbsup

[spooln30]

I think as long as the over dia is the same you'll be ok. Also a 225 will be ok on a 7.5 in rim.

[WickedSix]

with the varience between tire brands, the relative size differences you are looking at are negligible. Any of the three sizes you listed will work on the 18x7.5 wheel so long as they are the same at all 4 corners. Find a tire tread you like in one of the sizes and go with it. Narrower tires work better in ice/snow due to increased contact pressure so the 225 would serve this purpose, however if the tires will be used in all seasons the 235 is a good compromise between summer and winter performance.

Alot of places/people will tell you the OE went through XXX hours to find the right tire and wheel combination to best suit your vehicle...its malarkey...its just what they found to be the best compromise of cost/performance/packaging....as a vehicle enthusiast you know what the vehicle will be used for...find a set of tires that fit what your ma will be using the vehicle for

[Car Guy]

UPDATE: I had 225/50-17s Michelin Primacy MXM4 installed and my mother is very happy. Going from 255-45 to 225-50 on a 7.5" wheel made a world of difference, complete night and day. I know new tires always make a big difference but this comparison is to when the 255-45s were new. The ride went from pontoon boat like to very controlled and tracking very nicely. There is the smallest amount of outward sidewall taper but nothing that will cause any issues. I could not be happier with how everything went besides Michelin not carrying the MXV4 Primacy series in 225/50-17. A tire I prefer over the MXM4, ah well.....

[wrath]

It is important to note section width vs tread width. Some tires, especially under the Michelin name, are horribly narrow.

in a 275x55r20 tire, you will see a 1.75" difference between the narrowest and widest tread width P-metric tire in that size. Goodyear LS-2s are one of the widest.