PontiacBonnevilleClub.com

Ok, I admit I am blonde...so this is my question about tire sizes and what is ok to change and what cant be changed (not rims, jut the rubber).

For example, my bonne has 225/60/16 tires. I believe 60 is the width, so 50 would be a thinner tire, 70 wider. (obviously 16 is the rim size) ....now 225 how far can one veer from that? 215? 235? what changes if that number/size is messed with? odometer and gas mileage? handling? Thanks in advance!!

Deb

60 is not the width. It is the aspect ratio, AKA the height of the sidewall - the number is the percentage of the (section) width, which in this case is 225mm. A 225/60 will be "taller" than a 225/55 because it has more sidewall height. 60% of 225 = 135mm, 55% of 225 = 123.75mm.

In the end, in order to maintain factory clearance and not rub anything by going too big, and to avoid looking like you have four donuts by going too small, you will want to maintain the same overall height. The factory 225/60/16 tire has an overall height of ~26.6". If you are looking for wider tires for extra performance, 235/55/16 may be a reasonable size. Its overall height is 26.2", which results in plus ~1.8% speedometer error (as per this nifty tool.

Some possible rim/tires combinations that typically work with Bonnevilles and still maintain reasonable accuracy (of course, with different rim specs, YMMV):

235/55/16
245/55/16
225/55/17
235/55/17
235/45/18
245/45/18

thank you RepinS for explaining this to me!!