While moderating the BMW forums, one of the most common questions I answer is in regards to upgrading tires to a larger size. Using a wider size on the same wheel while maintaining the same overall diameter is known in the tire industry as "plus zero" sizing. This is typically done to get a larger contact patch and for an improved cosmetic appearance.
Here is a list of common plus zero sizes on two popular generations of BMW 3 Series vehicles:
E36 (most 1992-1998 BMW 318i, 325i, 328i, 330i models):
- If you have factory 16" wheels with the Original Equipment size of 205/55R16, you can install 225/50R16 tires with no problem. This is a very common upgrade and fits the wheels well. The plus size maintains the correct overall diameter and load requirements. With this change, you'll gain about an inch in tire width.
Below are two Firestone Firehawk Wide Oval Indy 500 tires. The tire on the left is a 205/55R16 and the one the right is size 225/50R16.
E46 (most 1999-2005 BMW 323i, 325i, 328i, 330i models):
- With the Original Equipment size of 205/55R16, you can use the plus size of 225/50R16.
- Owners with the O.E. size of 225/45R17 you can plus size to either 235/40R17 or 235/45R17. With the 235/45R17 size, it's a fit in a vast majority of cases and typically only rubs on a lowered vehicle or a car with worn suspension components.
- For the Original Equipment size of 225/40R18, the plus size of 235/40R18 will work. This is also a case where the plus size fits in the vast majority of cases and typically only rubs on a lowered vehicle or a car with worn suspension components.
For more information on this topic, read "Plus Size Wheels and Tires."