Diffrent tire sizes?
 

Hey guys, I know that running different tire sizes is not good for the x5, but for some dumb reason I thought that my spare on the x5 was the same as the rest of my tires that are 255/55/18 the spare is 235/65/17

I put the spare against the x5 to size it with the 18s and the spare is a bit bigger then the 18s that are on the x5, how bad is that to run on the x5? I have had the spare on for the past 2 to 3 weeks almost, would any thing have gotten damaged in that time?

If it is really bad would it be ok lets say if I get another flat to run the spare just to get me home or to a tire shop? normally I can plug it my self unless the tire blows up

Thanks

If you do the calculation, both 17" & 18" tire/wheel combo rolling diameters are relatively the same. Did you do the comparison when both tires are unloaded/loaded?

That is standard spare size; rolling circumference is nearly identical to oe 18" and oe 19" stock wheels.

As dkl noted, standing a tire/wheel combo up next to a tire/wheel mounted on car, will give false impression.

A handy tire/wheel combo size comparo site shows circumference of both combinations to be 91.2" and rotations per mile to be 694 & 695 = 'identical' for all practical purposes.

Not to worry...

Tire size calculator

GL, mD

Also look at the chart on your driver's door jamb (and owners manual)...and the recommended 17" tire size should be listed. The rolling diameter/circumference of all the recommended tires sizes is approx the same...at least within 3% (+/-) each other. :)

Just think about the 4.6is & 4.8is...they have the small 19" compact tire for the spare...that tire is way smaller than the 315/35/20 rear wheel...but the rolling diameter is the same.

BMW started giving different full spares around the early turn of the century (2000 - 2003 model year)...if you have a full sized spare...it is usually one of the lesser wheels if you have an upgraded size or more popular wheel.

well I knew from the 55 to the 65 that covers the 1 inch from 17 to 18 but I wanted to make sure, Thanks for all the info!!! learn something every day