Tire diameter increase - recode?

[tp2017]

If I change the OEM 17" tires on my 2016 BMW 320i xDrive to 18" wheels, does the vehicle need to be re-coded for the larger diameter wheels?

[328 Power 04]

The overall tire diameter remains unchanged though.

[tp2017]

Is that due to the tires in the 18" range having a shorter sidewall?

[328 Power 04]

Exactly

If you're using the factory tire size scheme, then the shorter sidewall makes for relatively the same diameter.

[bluptgm3]

This tire calculator (https://www.tyresizecalculator.com) should help

[visionaut]

There’s no ‘coding’ for tire diameters. OEM 20”, 19”, & 18” wheel/tire combos all have the same ~26.0” tire diameter. The larger diameter wheels are run with smaller aspect ratio tires (less sidewall) to retain the same overall diameter. Problems occur when folks venture away from OEM sizes, then the diameter can get too tall/short, a real problem if X-Drive…

[RBNetEngr]

If I change the OEM 17" tires on my 2016 BMW 320i xDrive to 18" wheels, does the vehicle need to be re-coded for the larger diameter wheels?

What you are asking about is known as a Plus 1 upgrade. If you increase the wheel size by 1” in diameter you would need to select an 18” tire that has the same diameter as the 17” tire does (within a 1-2%, if possible).

If you use a tire calculator like this, and enter your current 17” tire size, it will show you 18” a
(and other sizes as well) tires and their size comparison to the 17”.

https://tiresize.com/comparison/

For example, my 2014 328i came with 225/50R16 tires on it. But if I upgrade to a 17” wheel and choose a 255/40R17 tire, the overall tire size is very close, but the 17” tires will be wider.

https://uploads.tapatalk-cdn.com/20231031/66ea18dc8f13ec07ebf80d553eb968bd.jpg

Here is another calculator option that has a tab for alternate tire sizes:

https://tiresize.com/calculator/

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