33x12.50R20 vs 275/65R20 — the metric size is the taller one
A 20-inch pairing where the substitution runs upward rather than downward, which is not what the names suggest.
275/65R20 is 1.07 in taller than 33x12.50R20 (3.26%) and 1.67 in narrower. A speedometer calibrated for 33x12.50R20 would under-read by 3.26%.
Measured against each other
Overall diameter
33.00 in34.07 in+1.07 in (+3.26%)Section width
12.50 in / 318 mm10.83 in / 275 mm-1.67 in (-13.39%)Sidewall height
6.50 in7.04 in+0.54 inCircumference
103.7 in107.0 in+3.4 inRevolutions per mile
611.2591.9-19.3Ride height at the axle
——+0.54 inSpeedometer reading
——+3.26% under-read
| Dimension | 33x12.50R20 | 275/65R20 | Change |
|---|---|---|---|
| Overall diameter | 33.00 in | 34.07 in | +1.07 in (+3.26%) |
| Section width | 12.50 in / 318 mm | 10.83 in / 275 mm | -1.67 in (-13.39%) |
| Sidewall height | 6.50 in | 7.04 in | +0.54 in |
| Circumference | 103.7 in | 107.0 in | +3.4 in |
| Revolutions per mile | 611.2 | 591.9 | -19.3 |
| Ride height at the axle | — | — | +0.54 in |
| Speedometer reading | — | — | +3.26% under-read |
Calibrated for 33x12.50R20, running 275/65R20
- Dial reads 30
- 31.0 mph
- Dial reads 50
- 51.6 mph
- Dial reads 70
- 72.3 mph
- Odometer counts 100
- 103.3 mi covered
Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.
Substituting a metric size for a flotation one usually costs height. Here it gains 1.07 in.
The inversion, and its size
33x12.50R20 is 33.00 in. 275/65R20 works out to 34.07 in — a full inch taller, or 3.26%.
Section width goes the other way: 12.50 in down to 10.83 in, a reduction of 1.67 in or 13.39%. So the metric size is taller and considerably narrower, and neither tire is larger in both dimensions.
Why the sidewall matters more on a 20
Half an inch, 6.50 in against 7.04 in, which does not sound like much until you notice it is eight per cent of a rubber column that was short to begin with. On 20-inch wheels every fraction of sidewall is proportionally valuable, and the metric size has more of it despite being narrower.
The derived aspect ratio of the flotation tire is 52. The metric size states 65. Thirteen series apart, on tires an inch apart in height.
What the swap does
3.26%, with the metric size under-reading — around two and a quarter miles an hour at 70. The direction is worth registering, because a driver moving to a size described as "smaller" would expect the needle to run the other way, and the extra half inch of sidewall settles it instead.
Who this comparison is for
Owners who have been offered a 33-inch package and are wondering what the metric alternative gives up. The answer is that it gives up width and gains height, which is the reverse of the assumption most people bring, and it does so while asking less of the wheel — a 10.83 in section sits comfortably on factory 20-inch wheels where a 12.50 in one does not.
The tread trade
What the metric size gives up is not height but choice. Aggressive patterns on 20-inch wheels are overwhelmingly offered in flotation sizes, and 275/65R20 skews toward all-terrain and highway compounds sold as original equipment. A buyer who wants a particular mud-terrain pattern will usually find it in the 33 and not in the 275, and that constraint decides more of these comparisons than the inch of height does.
The taller end of the same wheel
285/65R20 reaches 34.59 in, and 35x12.50R20 reaches 35.00 in. Between them those two describe the top of what a 20-inch wheel will carry in general circulation.