Diffrent tire sizes?

[Moezer]

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

[dkl]

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?

[motordavid]

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

[Qsilver7]

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.

[Moezer]

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