[rallybull]

As per tirerack when you change wheels/tires the overall diameter should not change by more than +/- 1% , preferably +/- 0.5%

Now the 18" OEM wheels with 225/45 tires setup will have an overall diameter of 21.98" while the 19" OEM wheels with 225/40 tires will have a diameter of 22.51". That is more than half an inch diameter difference between the 18" setup and the 19" setup which actually happens to be a whopping 2.5% difference.

Is anyone is aware whether the cars that come with 19" from factory are coded differently than those with 18"? If you simply throw in a 19" setup on a car with existing 18" setup won't the odometer be off (I mean for every 100 miles you drive your odo will register 2.5 extra miles!!) ? Also won't that throw off the traction control system?

There are so many of you guys who have moved from 18" to 19" - have you'll given this a thought?

[infinitigor]

Stop worrying throw the 19s on and call it a day. Worst case scenario is your MPH reading is off by +- 2%

[rallybull]

Originally Posted by infinitigor

Stop worrying throw the 19s on and call it a day. Worst case scenario is your MPH reading is off by +- 2%

Worst case scenario could be odo putting on more miles (my warranty will expire in 39000 miles instead of 40,000) and issues with traction control. However, I refuse to believe that BMW will let the odo run faster than actual due to legal implications. I suspect the 19" cars are coded accordingly.

[remmib]

Originally Posted by rallybull

Now the 18" OEM wheels with 225/45 tires setup will have an overall diameter of 21.98" while the 19" OEM wheels with 225/40 tires will have a diameter of 22.51". That is more than half an inch diameter difference between the 18" setup and the 19" setup which actually happens to be a whopping 2.5% difference.

Where did you get those numbers, all wrong as far as I can see.

The 225/45/18 diameter is 26", and the 225/40/19 diameter is 26.1"

That's a 0.4% difference.

[ƒ°]

Your overal diameters are impossible. For 225/45/18, the diameter should be close to 25.9 inches. And for 225/40/19, it should be close to 26.1 inches.

21.98 inch total diameter on an 18 inch wheel would mean that the tire side-wall would be only 1 1/2 inch thick... that'd be like a 20 or 25 series tire.

[1bad335]

I made that very change a few months ago. Went from 18 inch sportline wheels with 225 square set up to BMW oem 403m 19 inch staggered wheels. There is no difference in my odo at all.

[cardnation]

You will be fine. You could also go with 245/35/19 which would be 25.86" vs 225/45/18 which is 25.91"

[rallybull]

Originally Posted by remmib

Where did you get those numbers, all wrong as far as I can see.

The 225/45/18 diameter is 26", and the 225/40/19 diameter is 26.1"

That's a 0.4% difference.

Originally Posted by Number

Your overal diameters are impossible. For 225/45/18, the diameter should be close to 25.9 inches. And for 225/40/19, it should be close to 26.1 inches.

21.98 inch total diameter on an 18 inch wheel would mean that the tire side-wall would be only 1 1/2 inch thick... that'd be like a 20 or 25 series tire.

You guys are right. I forgot to add the thickness of the side wall twice

Originally Posted by 1bad335

I made that very change a few months ago. Went from 18 inch sportline wheels with 225 square set up to BMW oem 403m 19 inch staggered wheels. There is no difference in my odo at all.

Makes sense given that my calculations were way off.

Originally Posted by cardnation

You will be fine. You could also go with 245/35/19 which would be 25.86" vs 225/45/18 which is 25.91"

That is an interesting point. Never thought of going wider on the front with 245/35. But I'm a bit wary that may cause rubbing with the lowered M-Perf suspension. Actually the 225/40 is not even available for the Micehlin Pilot A/S 3 so if I have to go with that tire, I will either need to move up to 245 or go with 18" instead of 19".

[trey100]

Your math is wrong. 225/45/18 is:

45% of 225 for EACH side of the wheel. So, 100 mm x 2 = 7.97". Plus the 18" wheel is 25.97"

For the 225/40/19:

40% of 225 is 90 mm each side of the wheel. So, 2 x 90 mm = 7.08". That plus the 19" wheel is 26.08".

[teen335]

Hopefully this can help you

www.1010tires.com/Tools/Tire-Size-Calculator