GarageCalc How to read the 18-inch chart
Every size here fits an 18-inch wheel, but they are not interchangeable: the diameter spread is 10.9 in between the shortest and the tallest. 34 of the 54 sizes have an aspect ratio of 55 or lower, the low-profile end used on cars, while 14 sit at 65 or higher, the tall-sidewall sizes used on trucks, SUVs and vans.
To swap sizes on the same wheel, stay within 3 percent of the original diameter and check that the wheel width suits the new tire width. The comparison calculator shows the speedometer error for any pair, and the offset calculator covers clearance if the wheel changes too.
Frequently asked questions
What is the most common 18-inch tire size?
Width 245 mm appears most often in the 18-inch catalogue, across 8 aspect ratios. Which one your car takes depends on the placard in the door jamb; the chart lists all 54 sizes so you can read the diameter of each.
How tall are 18-inch tires?
Anywhere from 23.9 in (215/35R18) to 34.8 in (305/70R18) in overall diameter. The wheel is always 457 mm; the sidewall, which is width times aspect ratio, decides the rest.
Can I put a different 18-inch tire size on the same wheel?
Yes if the overall diameter stays within about 3 percent of the original and the rim width suits the new tire width. Each size page lists the sizes that qualify, on this wheel and one size up or down.