I have been reading some forums but finding a clear answer is tricky as so many variables come into play. I am curious if these wheels/tire sizes would fit a 2006 530i stock suspension (non-sport). Will there be rubbing issues? Should fenders be rolled? Would spacers help (3/4")?

Sizes are 255/40/19 front and 285/35/19 rear. Why would someone want the front tire a 40 when the back is a 35? Dont they need to be the same?

Thanks

 

To answer your question you have to understand what the 40 and 35 numbers mean. The middle number determines the thickness of your sidewall which in turn tells you the outside diameter of a tire.

To calculate the sidewall you take the first number (255) multiple it by the ratio (40) and divide by 100. (255 * 40) / 100 = 102mm. To convert to inches you divide 102 by 25.4 = 4.02". To find the outside diameter you double the sidewall and add the last number in the tire specs (19).

(4.02 * 2) + 19 = 27.04"

Now if you did the same for the rear tire 285/35/19 you'd realize the outside diameter is 26.85" and the sidewall is 3.93".

If we did the rear the same as the front 285/40/19 you'd have a really large sidewall (4.5") compared to the front and the outside diameter would be 27.98.

Now those sizes you listed are the incorrect sizes. You should run 245/35/19 and 275/30/19 because that will give you the closest outside diameter to OEM wheels. This is important because the speedometer and odometer are calibrated to the tire's outside diameter.

FYI...

245/35/19 Outside Diameter 25.75 Sidewall 3.38
285/30/19 Outside Diameter 25.73 Sidewall 3.37

Notice how close the numbers are? That's your goal. Hope that made sense.

Michael
Owner
Acute Performance

 

Not enough info to answer your question since you did not specify the offsets.

Assumptions
1. You have M5 offset

You cant fit 255/40/19 on your front

You need the front to be 245/40/19

For your rear -- 285/35/19 should be good to go


"Why would someone want the front tire a 40 when the back is a 35? Dont they need to be the same? "
This question has been answered multiple times in different posts, please use the search feature.

 

The wheels came off a 2008 M5. I am guessing the offset would be for an M5. Thanks for the education on the tires. I will use that formula as I look for rims. I am thinking I will just buy rims without tires and do my own setup to get the right fit. Thanks guys, love the knowledge this forum has!!

 

Great explanation, Mike. I've wondered about the tire sizes myself.

Thanks,