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Size comparisons

285/70R17 vs 35x12.50R17 — the step a Rubicon usually takes

The most common one-move upgrade on a factory 33, and the point where stock gearing first becomes a topic.

285/70R1732.71 in tall11.22 in wide35x12.50R1735.00 in tall12.50 in wide+2.29 in · +7.01%
Drawn to scale from the size codes. Solid outline is 285/70R17; dashed outline is 35x12.50R17. The bars below each tire are section width at the same scale.

35x12.50R17 is 2.29 in taller than 285/70R17 (7.01%) and 1.28 in wider. A speedometer calibrated for 285/70R17 would under-read by 7.01%.

Measured against each other

  • Overall diameter

    32.71 in35.00 in+2.29 in (+7.01%)

  • Section width

    11.22 in / 285 mm12.50 in / 318 mm+1.28 in (+11.40%)

  • Sidewall height

    7.85 in9.00 in+1.15 in

  • Circumference

    102.8 in110.0 in+7.2 in

  • Revolutions per mile

    616.6576.2-40.4

  • Ride height at the axle

    ——+1.15 in

  • Speedometer reading

    ——+7.01% under-read

Calibrated for 285/70R17, running 35x12.50R17

Dial reads 30
32.1 mph
Dial reads 50
53.5 mph
Dial reads 70
74.9 mph
Odometer counts 100
107.0 mi covered

Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.

Two and a quarter inches, all of it sidewall, on the wheel the vehicle already has. This is the most-taken single step in the 17-inch off-road world.

The sidewall reaches nine inches

The rubber column reaches a round 9.00 in, from 7.85 in. On a 17-inch wheel that is close to the practical ceiling: a taller flotation size would need a taller sidewall still, and 37x12.50R17's 10.00 in is where packaging under an unmodified body generally stops.

The width change is modest by comparison — 11.22 in to 12.50 in, 1.28 in, 11.40% — which is why this step is discussed in terms of height almost exclusively.

Seven per cent, and the gearing question

This is the magnitude at which the gearing conversation starts. From a 4.10:1 axle the arithmetic asks for 4.39:1, with 4.30:1 the nearest ratio sold; from 3.73:1 it asks for 3.99:1 against an available 3.91:1. Neither is a match, and neither is a recommendation — they are conversions of one ratio into another at a fixed road speed.

Two vehicles, the same numbers

Both the Wrangler JL and the Gladiator are delivered on 285/70R17 in their off-road trims, and both have owners who step to 35x12.50R17. The arithmetic is identical; the packaging is not, since one vehicle has a bed and a longer wheelbase behind the same front end.

Ride height and what it does not do

Whatever the axle gains, the crown of the tire takes back from the arch, so the vehicle stands higher and has less room than it started with — the mechanism is set out in overall diameter, loaded radius and rolling radius. On a vehicle with a removable top and doors, incidentally, the sequence matters: the gap that gets tighter is the one measured with the suspension fully compressed, which is not a position anyone checks in a car park.

At the instruments the same step is 7.01%, which is the region where a cluster recalibration starts being worth doing rather than carrying.

The notation switches at this rung

Below 35 inches there are metric options at nearly every height. At 35 there effectively are not: the largest common metric size on a 17-inch wheel is 315/70R17 at 34.36 in, and it is 0.64 in short. So this is the step where an owner leaves metric notation behind and starts buying flotation sizes, which is a change in how the tire is specified as much as in how big it is.

The step beyond

285/70R17 against 37x12.50R17 is 4.29 in and 13.12% — nearly twice this — and it is where the axle ratio arithmetic stops being a curiosity.

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