[MinscLovesBoo]

Greetings and first post.

I’ve done searching while lurking however haven’t found this specific question.

We are about to order a 2020 M40i with 19s. For where we live running winter tires doesn’t make sense due to local snowfall and temps and some of our driving routes; BUT we do need to head through some mountain passes which can have large amounts of snowfall (Northern Nevada) for trips into CA where we might have 60 plus degree temps that would be...bad...for winter tires.

Vredestein (sp?) has some all season severe snow rated and w/y rated tires however they are 245/45 vs the 245/50.

Other than all the usual effects of a smaller sidewall, has anyone done something similar or aware of any potential issues with the systems in an M40i?

Thank you!

[chassis]

Shorter sidewall in the 45s will be harsher and slappier. Whether it is acceptable or unacceptable is your judgment to call.

[Opie55]

Your speedo will read a bit higher. But that car uses a 50 aspect ratio tire? That seems large. But assuming that is correct, besides the speedo error the only issue would be appearance. Have not paid much attention to the new 6s, but most people think the fender gap is already too big. Dropping from 50 to 45 on that width tire is a full half inch smaller sidewall. That's noticeable. The gap may look funny that big. The entire wheel will be an inch smaller. My daughter has an Audi A4 with the opposite issue. Somebody put tires for an AllRoad wagon on it, and they are 5 (or 1/2 inch) larger. You wouldn't think a half inch would make that much difference, but they look too big.

EDIT: Ignore the part of my comment questioning the aspect ratio of 50 - I was thinking I was still in the 6 series forum. But the tire will still be noticeably smaller, although gap is less of an issue in an X3.

[MinscLovesBoo]

Originally Posted by chassis

Shorter sidewall in the 45s will be harsher and slappier. Whether it is acceptable or unacceptable is your judgment to call.

Agreed - however switching from the run flats to normal will soften the ride significantly (based on previous experience I’ve had with run flats)...so I’m thinking it will at worst case end up a wash. We will see though.

[oVeRdOsE.]

Originally Posted by chassis

Shorter sidewall in the 45s will be harsher and slappier. Whether it is acceptable or unacceptable is your judgment to call.

side wall 4.3'' VS 4.8'' (11%)
diameter 27.7'' VS 28.6'' (3.2%)

doubt he will feel any difference.

[doodlebro]

Originally Posted by oVeRdOsE.

side wall 4.3'' VS 4.8'' (11%)
diameter 27.7'' VS 28.6'' (3.2%)

doubt he will feel any difference.

That's actually plenty to feel. Ride will be slightly harsher.

[jcmbmw]

What about mileage on odometer? Any big difference?

[Alfisti]

Ideally you do not change the sidewall and not change the width. 245/50 is 122mm of sidewall, 245/45 is 110mm. That is a HUGE drop. Your wheel is 483mm so your existing rolling circumference is 605mm and you are proposing moving it to 593mm.

605-593 = 12

12/605 = 2%

That should be fine. Rule of thumb is 3% absolute max.