I'm currently on 225/50/17 tires and 17x7 rims. Can I safely switch to 225/45/17?

~THT

 

Yes, you can.

 

How about going wider to 235/45/17?

~THT

 

Last question first: 235/45's on 7" wheels has been discussed ad nauseum (and it's still an out-of-spec fitment by half an inch of rim width).

225/45's are OK, but since it's a slightly smaller tire in terms of load capacity you should run about 4 psi or so more in them than the tire sticker calls for in order to match what your car's originals were good for at the sticker inflation pressure.

Norm

 

Thanks for the input. If 235 is an out-of-spec width for a 7" rim, why would Tirerack suggest a 235/45/17 tire size for a that size?

~THT

 

It's a case where the size (235/45) is OK for the car, but not the wheel. You should be satisfying both sets of requirements whenever you change tire size.

Be careful of what was not provided on that search results page. Notice that no mention was made as to wheel width, nor was that one of the search parameters. TR's search engine has no way of knowing what size wheels you have or may be intending to purchase, nor the sizes on Maximas for which tires were sold in the past. Hence that listing is being made on the basis of things like load capacity and outer diameter/revolutions per mile for reasons of guaranteed clearance, speedometer accuracy and perhaps some ABS considerations as well. This page only satisfies the car's requirements.

When you dig deeper into Tire Rack's database you can find out the permissible rim width ranges for most (if not all) of the tires that they sell. Click on the 'SPECS' tab or link for any specific tire make/model, and you'll find one column for the "measuring width" and another for the range of acceptable rim widths for the available sizes. Here's where you find out what the tire needs, or alternatively, what your wheels are acceptable for.

Norm

 

Once more, thank you for the very informative post.

When I selected a 17x7 wheel, they recommended a 235/45/17 tire to go with it; is that still fitting just the car's requirements? I checked the Specs link for the Pirellis that I'm interested in and the 215 model is recommended for 7" wheels. I really don't want that narrow of a tire and my 225s have been riding just fine. What are the negatives of using an out-of-spec tire (say 225 or 235 on my 7" rims)?

~THT

 

Yes. I have yet to see a 235/45-17 tire that was approved for a 7" rim width. Nor have others who have investigated this. AFAIK, it's a Tire & Rubber Association industry-wide spec that 7.5" be the minimum width for this size. It's entirely possible to design a tire to behave properly on a narrowish wheel, but it would probably have to be sold as some sort of special-purpose tire. Actually, exactly this has been done for certain racing tires that used a rather extreme cantilever construction to help racers get around sanctioning body wheel width regulations. But I digress . . .

Tires are designed with a specific flex point in the sidewalls, and that goes with a specific rim width (best bet would be the "measuring width"). Going wider or narrower than that moves the flex point up or down the sidewall, and there is some tolerance for this. Ultimately, there is a limit as to how far you can allow the flex point to migrate before you push it into a region of the sidewall that isn't intended to cope with the maximum flexing. Heat builds, as do the adverse effects.

That's why there's a range of acceptable widths for any given nominal tire size. Yes, there's some margin, and that's certainly one reason that those who have actually put 235/45's on the OE wheels have not been reporting failures. Another is that this is not a binary "absolutely-good/guaranteed failure" issue, and the 235's are just barely out of spec. But for official guidelines that carry some legal weight, a firm line has to be drawn somewhere.

Now consider that if you're using up some of the overall safety margin by improper fitment (maybe even a disproportionately large amount of said margin) you're leaving yourself less in reserve to cover maximum vehicle loading (or the slight overloading that everybody knows occurs on occasion), extended high speed summertime running, unusually hard driving, occasional inadvertent underinflation, etc., or any combination of the above. I suppose that if you never encountered any of those conditions or others that I have missed you could run the 235's in a reasonable semblance of safety. But you'll never get a recommendation of 235/45's on 7's as from me - that would be far too irresponsible.

Norm

 

Either 225/45 or 225/50 is in spec on 17 x 7's. If you're looking at the P6 Four Seasons specs I understand that question better now, as I've seen the P6 4S table to be incomplete.

Separate post for clarity

Norm