i was wodering this cause im getting new tires/rims. what do bthey mena and how do u convert the metric measurements to customary. swo i can get an ideaof the wideness andheight of the tirs im looking at

 

The three numbers represent width height and inside diameter.

Using 245/45-18 as an example:

-245 is the width in mm.

-45 is the height of the sidewall as a percentage of width, so 45% of 245mm is 110.25mm

-18 is the diameter of wheel the tire fits in inches.

 

One more thing I forgot. There are 25.4 mm in an inch.

 

or 2.54 cm/inch.
one of my few metric conversion factors, other than a kilometer being about 0.6 mile. I know...FWIW.

 

yup 2.54, very important to remember, wish I could remember how many grams in a lb. owell 454 I think... who knows.

anyway, also for you purposes, quick math dictates that stock tires are 245/45/18, MEANING that you have 110mm of sidewall. this is what you want to duplicate if you get 18" rims regaurdless of rim width, you want 110mm of sidewall.

if you go to 19" rims you added .5" of rim, meaning you need .5" less of sidewall, 25.4mm/inch/2, is 12.7mm less of sidewall, meaning you want about 98mm of sidewall, do the reverse math and depending on width of tires in question, you figure out the percentage that gets you the closest to the overall stock diameter.