How tall is a 33 inch tire, really?
Answer
32.99–33.06 in
"33-inch" is a category, not a measurement. Of the sizes in this catalogue that people call 33s, the geometric diameters run from 32.99 in to 33.06 in — a spread of 0.07 in between tires sold under the same name.
The working
- 33x12.50R15
- 33.00 in tall, 12.50 in wide
- 33x12.50R16
- 33.00 in tall, 12.50 in wide
- 33x10.50R17
- 33.00 in tall, 10.50 in wide
- 33x12.50R17
- 33.00 in tall, 12.50 in wide
- 33x12.50R18
- 33.00 in tall, 12.50 in wide
- 33x12.50R20
- 33.00 in tall, 12.50 in wide
- 275/60R20
- 32.99 in tall, 10.83 in wide
- 255/80R17
- 33.06 in tall, 10.04 in wide
The one call size that mostly tells the truth
Ask this question about a 31 or a 35 and the honest answer is a range with an argument in it. Ask it about a 33 and the answer is boring: 33.00 in. Every flotation size written 33x-something states its diameter in the code, so a 33x12.50R17, a 33x12.50R20 and a 33x10.50R17 are all exactly 33.00 in by construction, differing only in width and in which rim they mount on.
The metric neighbours are closer than usual too
275/60R20 comes out at 32.99 in and 255/80R17 at 33.06 in. Both are within a rounding error of the flotation figure, which is not something the 35-inch or 31-inch groups can claim.
Where the 33 label starts stretching
The looseness is on the shoulders of the group, among sizes that are marketed and discussed as 33s without being one:
- 285/70R17 — 32.71 in. The most commonly quoted "33" in metric, and 0.29 in short of the mark.
- 285/75R16 — 32.83 in. The 16-inch version of the same idea, and slightly closer.
- 275/70R18 — 33.16 in. Over the line rather than under it.
- 295/70R17 — 33.26 in. The tallest thing anyone reasonably calls a 33.
That is a spread of about half an inch from the shortest to the tallest, all under one name. A quarter of an inch either side of nominal decides nothing about a speedometer and can decide everything about a fender liner.
Reading a claim about someone else's 33s
Two people running "33s" may be 0.55 in apart, which puts a little over a quarter of an inch of ride height between them at the axle. That is why every comparison on this site is built from the size code rather than the nickname — put any two of the sizes above into the comparison tool and the difference is stated in inches rather than in labels. If you want the general rule behind the flotation numbering, the metric versus imperial notation page explains why one of these two systems can state a diameter and the other cannot.