Tire size question
 

Merry Christmas, Happy Holidays and Happy New Year to all my BMW buddies :)

Not sure where to put this so the lounge is a good default.

Really, really, can I use 275/40/20 tires on 285/40/20 rims and 315/35/20 tires on 325/35/20 rims?

Some of you have the background on my 50i vs ///M saga. I went backwards to a 50i because I wanted runflat tires and no one makes them in the 285 & 325 sizes above. Fast forward, I was very disappointed in the 50i and traded it in for the ///M. So here we go....

I asked my tire vendor and he said they would fit, he would do it if it was my car but being brand new, lease, etc he wouldn't do it unless BMW told me OK in writing. While at the dealer, I was speaking to the parts manager and he said they do it all the time. It's only 10 mm which is less than half an inch.

So, what do you guys think? JCL, you're always a wealth of knowledge. I really appreciate any info.

Thanks all.

It'll fit just fine. You will have a 1% speed variance on your speedometer, however.

Thanks!

Jeff,
As you may recall, L doesn't drive the speed limit anyway...that 1% is a rounding error for her. ;)

PS: I agree on the fit.

Of course I drive the speed limit. I'm just wondering which way the 1% goes :dunno:

Hi mD!

;) Lol!

Using my handy PowerDog site, the newer tire set of 275 and 315s vs 285 and 325s, shows a difference of:

704 vs 696 revolutions per mile, (275/315s vs 285/325s)...about a 1% diff.

With the 'original size' of 285s/325s vs the proposed new size of 275s/315s,
the original set at 60 mph on a speedo would theoretically show 61 mph at same speed. Not biggie, imo.

And factor in that the BMW speedos are a tad optimistic anyway, and I wouldn't give it any concern.

Keep that new M under a buck and a half and between the fences. :)
Happy New Year, L :hug:

Tire size calculator

The gurus have already spoken, but I'd do it without a worry.

Happy New Year to all.

Jeff

Thanks Jeff, mD and Jeff for ll your info.