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Size comparisons

275/60R20 vs 285/65R20 — the AT4 step, casing over size

A Sierra's factory tire against the size above it, where the change in load rating is as consequential as the change in geometry.

275/60R2032.99 in tall10.83 in wide285/65R2034.59 in tall11.22 in wide+1.59 in · +4.83%
Drawn to scale from the size codes. Solid outline is 275/60R20; dashed outline is 285/65R20. The bars below each tire are section width at the same scale.

285/65R20 is 1.59 in taller than 275/60R20 (4.83%) and 0.39 in wider. A speedometer calibrated for 275/60R20 would under-read by 4.83%.

Measured against each other

  • Overall diameter

    32.99 in34.59 in+1.59 in (+4.83%)

  • Section width

    10.83 in / 275 mm11.22 in / 285 mm+0.39 in (+3.64%)

  • Sidewall height

    6.50 in7.29 in+0.80 in

  • Circumference

    103.6 in108.7 in+5.0 in

  • Revolutions per mile

    611.3583.1-28.2

  • Ride height at the axle

    ——+0.80 in

  • Speedometer reading

    ——+4.83% under-read

Calibrated for 275/60R20, running 285/65R20

Dial reads 30
31.4 mph
Dial reads 50
52.4 mph
Dial reads 70
73.4 mph
Odometer counts 100
104.8 mi covered

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

The dimensional change here is ordinary. The change in what the tire is built to carry frequently is not, and that is the part worth attention.

The dimensions first

Ten millimetres of casing and five points of profile, which come to 1.59 in of diameter — most of it bought by the profile step, since 0.80 in of extra sidewall on an unchanged wheel is the whole of the height. On the dial that is roughly three and a half miles an hour missing at motorway pace, and nothing there requires an allowance to be made.

The part that is not geometry

285/65R20 is widely offered as an LT-marked tire and 275/60R20 frequently is not. An LT casing is built to a different standard: heavier construction, a much higher reference inflation pressure, and a load index derived from what the casing holds at that pressure rather than at the passenger-tire reference.

Two tires of the same nominal size, one marked LT and one not, can differ by hundreds of pounds of rated capacity each. On a half-ton that tows or carries, that difference matters considerably more than the 1.59 in above — and it is invisible in every dimension this site computes.

The number the vehicle requires is on the door-jamb placard, stated as a load index and a cold inflation pressure. It does not change when the tire does.

Pressure follows construction, not size

A consequence worth stating: if the replacement tire is an LT and the original was not, the cold inflation pressure that achieves the placard's load is different, and often considerably higher. Running an LT casing at the pressure printed for a passenger-construction tire under-inflates it for the load. That is an arithmetic relationship between load tables and pressure rather than a recommendation, and the load range reference sets out how the two are connected.

Because it is the largest metric size commonly stocked for a factory 20-inch wheel, it lands within half an inch of a nominal 35, and it does so without any flotation-size complications. For an owner who wants the height and the load rating together, it is the only mainstream option.

The smaller and larger neighbours

Below: 275/55R20 to 275/60R20, one profile step at 1.08 in. Above: 35x12.50R20, which is 0.41 in taller and 1.28 in wider, and which brings the rim-width question with it.

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