255/75R17 vs 33x12.50R17 — under an inch of height, two and a half of width
A Sahara's factory tire against the first flotation size above it, where the width increase dwarfs the height increase.
33x12.50R17 is 0.94 in taller than 255/75R17 (2.94%) and 2.46 in wider. A speedometer calibrated for 255/75R17 would under-read by 2.94%.
Measured against each other
Overall diameter
32.06 in33.00 in+0.94 in (+2.94%)Section width
10.04 in / 255 mm12.50 in / 318 mm+2.46 in (+24.51%)Sidewall height
7.53 in8.00 in+0.47 inCircumference
100.7 in103.7 in+3.0 inRevolutions per mile
629.1611.2-17.9Ride height at the axle
——+0.47 inSpeedometer reading
——+2.94% under-read
| Dimension | 255/75R17 | 33x12.50R17 | Change |
|---|---|---|---|
| Overall diameter | 32.06 in | 33.00 in | +0.94 in (+2.94%) |
| Section width | 10.04 in / 255 mm | 12.50 in / 318 mm | +2.46 in (+24.51%) |
| Sidewall height | 7.53 in | 8.00 in | +0.47 in |
| Circumference | 100.7 in | 103.7 in | +3.0 in |
| Revolutions per mile | 629.1 | 611.2 | -17.9 |
| Ride height at the axle | — | — | +0.47 in |
| Speedometer reading | — | — | +2.94% under-read |
Calibrated for 255/75R17, running 33x12.50R17
- Dial reads 30
- 30.9 mph
- Dial reads 50
- 51.5 mph
- Dial reads 70
- 72.1 mph
- Odometer counts 100
- 102.9 mi covered
Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.
Less than an inch taller. Two and a half inches wider. That imbalance is what makes this step feel much larger than the diameter figure suggests.
The two changes, side by side
Overall diameter rises 0.94 in, which is 2.94%. Section width rises 2.46 in, which is 24.51%.
The first of those is inside the range that tire wear alone produces over a set's life. The second is a quarter of the casing added in one move, and it is where the whole character of the change lives.
What the speedometer does
Revolutions per mile falls from 629.1 to 611.2 — eighteen fewer rotations in every mile. That count is the whole of the mechanism. Nothing on the dash measures road speed or distance directly; each display takes the rotation count and scales it, so all of them are wrong by one proportion or none of them is.
Nobody re-gears for this, and the arithmetic agrees. The conversion from 3.73:1 returns 3.84:1, a number sitting in the gap between two sets anyone sells and not worth chasing.
The shapes are quite different
The metric size is a stated 75-series with a 7.53 in sidewall on a narrow casing. The flotation size works out to a 64-series with an 8.00 in sidewall on a very wide one. Half an inch more sidewall, two and a half inches more width — the 33 is a much squatter object built to the same wheel.
Why this is the step that "usually clears"
Because 0.94 in of extra diameter is a small demand on the arch, and the vehicle's remaining constraint is width at full lock rather than height. Whether the width clears depends on wheel backspacing and on the steering stops, which are properties of the vehicle and its wheels rather than of the tire.
The rim the flotation size wants
Neither of these codes contains a rim width, and neither does this site's data. What the arithmetic can say is that the flotation casing is 2.46 in wider in nominal terms, 10.04 in against 12.50 in, and that the wider a casing is the more the wheel underneath it matters. Put one on a rim narrower than the one its width was quoted against and the crown rounds off: width falls below the nominal figure and height climbs above 33.00 in, the one paying for the other. The shift is a few tenths at most — but the entire height difference on this page is 0.94 in, so a few tenths is a meaningful share of the answer, and it is decided by the wheel rather than by either size code.
The bigger jump from the same start
255/75R17 against 35x12.50R17 keeps this same 12.50 in width and adds two more inches of height — the same width consequence, three times the diameter change, and a completely different conversation about gearing.