245/75R17 vs 33x12.50R17 — a Gladiator's first upgrade
The base Gladiator size against the size most of them end up wearing, on a truck whose extra length changes what the tire has to clear.
33x12.50R17 is 1.53 in taller than 245/75R17 (4.87%) and 2.85 in wider. A speedometer calibrated for 245/75R17 would under-read by 4.87%.
Measured against each other
Overall diameter
31.47 in33.00 in+1.53 in (+4.87%)Section width
9.65 in / 245 mm12.50 in / 318 mm+2.85 in (+29.59%)Sidewall height
7.23 in8.00 in+0.77 inCircumference
98.9 in103.7 in+4.8 inRevolutions per mile
640.9611.2-29.7Ride height at the axle
——+0.77 inSpeedometer reading
——+4.87% under-read
| Dimension | 245/75R17 | 33x12.50R17 | Change |
|---|---|---|---|
| Overall diameter | 31.47 in | 33.00 in | +1.53 in (+4.87%) |
| Section width | 9.65 in / 245 mm | 12.50 in / 318 mm | +2.85 in (+29.59%) |
| Sidewall height | 7.23 in | 8.00 in | +0.77 in |
| Circumference | 98.9 in | 103.7 in | +4.8 in |
| Revolutions per mile | 640.9 | 611.2 | -29.7 |
| Ride height at the axle | — | — | +0.77 in |
| Speedometer reading | — | — | +4.87% under-read |
Calibrated for 245/75R17, running 33x12.50R17
- Dial reads 30
- 31.5 mph
- Dial reads 50
- 52.4 mph
- Dial reads 70
- 73.4 mph
- Odometer counts 100
- 104.9 mi covered
Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.
The height change here is modest. The width change is not, and on a Gladiator that ordering matters more than it would on a Wrangler.
Six times more width than height, proportionally
- Diameter: +1.53 in, +4.87%
- Section width: +2.85 in, +29.59%
Nearly thirty per cent more casing for under five per cent more height. Anyone reading only the diameter row is reading the smaller of the two numbers by a wide margin.
Why the truck's length is part of this
A Gladiator carries the same front end as a Wrangler and adds a bed and a longer wheelbase behind it. The consequence is that the tire's height meets the same front-arch geometry as on the shorter vehicle, while the extra width has more places to interact with — the rear arch openings and the bed sides sit differently over the rear axle than a Wrangler's body does.
None of that is measurable from a size code, and it is the reason the two vehicles' owners reach different conclusions from identical arithmetic.
The differential arithmetic lands on a real set
Run a 3.73:1 axle through the ratio and it comes out at 3.91:1 — a set that is actually manufactured, so the conversion needs no rounding at all. A 4.10:1 axle comes out at 4.30:1, also available. Both are conversions rather than proposals: the ratio that reproduces one engine speed given another, with no opinion attached about whether anyone should fit it.
The instruments are the small print by comparison: under five per cent, which is the region most owners carry rather than correct.
The sidewall, and the shape change
Three quarters of an inch of extra sidewall, 7.23 in against 8.00 in. The metric size is a stated 75-series; the flotation size works out to a 64-series. So the 33 is not simply a bigger version of the base tire — it is a squatter, wider shape that happens to be taller as well.
What the spare carrier is holding
A Gladiator's spare hangs under the bed rather than on a tailgate, in a position sized around the factory tire. A 33.00 in tire on a 12.50 in casing is a substantially bigger object than a 31.47 in one on a 9.65 in casing, and whether it stows is a question about the carrier and the winch rather than about either size code. It is the detail most often discovered after the tires have been bought.
The bigger move
245/75R17 against 35x12.50R17 keeps this width and adds another two inches of height, which is the step Gladiator owners most often take next and the one where gearing enters the discussion.