illus83

Has anyone considered going to a 265/40/21 tire on their SQ5? It wouldn't hurt to have a slightly wider look and you get a few more options to choose from going with that size.

Reggie

How will that affect the odometer?

There are websites that can tell you

JBDinTX

Don't think wider would effect the speedo. Just taller.

ND40oz

Wider is taller if the second number doesn't change, since it's the ratio of height to the width.

Doesn't look like there are any really better options at 265 or even 275.

Yoshimura

Those are nominal dimensions and thus not all tires of a particular dimension have the same width and/or height. Some 255/45 are actually taller than some 265/45. You need to check the tire specification for actual dimensions.

Regarding spedometer accuracy, you need to check Revolutions Per Mile specification. Because all tires doesn't flex the same way, two different tires with the same height (or diameter) could have different number of revolution per mile. Some 255/45 actually turns less per mile than some 265/45.

Here's a picture of two 255 tires on 8.5" wheels...

ND40oz

Yeah, there are slight variances between manufacturers and specific tires, but if you compare two of the same exact tire, a 265/40/21 will be taller then a 255/40/21.

A 265/40/21 should be 265mm wide with a sidewall height of 106mm (265x.40).

A 255/40/21 should be 255mm wide with a sidewall height of 102mm (255x.40).

SQive

That is exactly what I intend to do. I have the 21" Pirellis and they are too narrow for my taste. I'm actually thinking of going with 275/40R21. That currently limits my selection to the Dunlop SportMax, but it's a good-looking tire. Alternately, I may go with the Continental CrossContact UHP in 265/40R21. They are a slightly harder compound, so treadwear would be better, although handling may suffer.

If the 275's will fit the front with my 12.5mm spacers, then that's what I'll go with. If not, I'll go with the 265's. There is no problem with the back. The only issue is in the front, with the upper-control arms at the top of the tire. You should take a measurement for yourself, but I don't think there will be any problem with the 265's.

Personally, I like a little belly on my tires. Call me "old school," and it may not be as good in handling, but I think it looks far better and you don't have to worry so much about curbing the rims. I also like a little more sidewall in case of potholes.

Here is the site where you can get (fairly) exact measurements for various tire sizes and offsets: Custom rims, wheel tire packages for your ride - RIMSnTIRES.com. It also gives you the speedometer variation. The 265 is only 0.3" larger in diameter, which puts the speedometer 1.2% slower, so 60 MPH will actually be 60.7 MPH. That's really not an issue and it will shave a few miles of the odometer in the long run. The 275 would be 2.2%, or 61.3 MPH. That is not a problem for me at all. I only have 4K miles on these Pirellis, but I am looking forward to wider shoes...except for the price, of course.

illus83

I'm with you. I prefer the wider look. I ran a calculation as well between a 255 vs 265 and the variance was only 1%.

It would be great if we could run 275's all the way around. I wonder how the sidewalls would look? You're right about the clearance for the fronts. I imagine you'd be good with 12.50 mm spacers?

MP4.2+6.0

Anything beyond a 255 in a 40 is a 9" min. wheel spec typically.

SQive

The 12.5mm spacers in the front make the offset 20.5mm. I have 20mm spacers in the back, making it 13mm.
Ideally, I would get some 20x10 et15 wheels with 295/40R20 tires. That would only be 0.3" taller, and the width would be 11.8".
However, I got these stock 21" wheels because I really like the way they look, and I got the extended wheel and tire coverage to boot...so there's that.