GarageCalc How to read the 21-inch chart
Every size here fits a 21-inch wheel, but they are not interchangeable: the diameter spread is 3.8 in between the shortest and the tallest. 19 of the 19 sizes have an aspect ratio of 55 or lower, the low-profile end used on cars, while 0 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 21-inch tire size?
Width 255 mm appears most often in the 21-inch catalogue, across 4 aspect ratios. Which one your car takes depends on the placard in the door jamb; the chart lists all 19 sizes so you can read the diameter of each.
How tall are 21-inch tires?
Anywhere from 28.0 in (255/35R21) to 31.8 in (275/50R21) in overall diameter. The wheel is always 533 mm; the sidewall, which is width times aspect ratio, decides the rest.
Can I put a different 21-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.