255/80R17 vs 285/70R17 — same height, 30 mm apart
Two very different casings that arrive at almost the same diameter, and the reason an 80-series exists at all.
285/70R17 is 0.35 in shorter than 255/80R17 (1.07%) and 1.18 in wider. A speedometer calibrated for 255/80R17 would over-read by 1.07%.
Measured against each other
Overall diameter
33.06 in32.71 in-0.35 in (-1.07%)Section width
10.04 in / 255 mm11.22 in / 285 mm+1.18 in (+11.76%)Sidewall height
8.03 in7.85 in-0.18 inCircumference
103.9 in102.8 in-1.1 inRevolutions per mile
610.0616.6+6.6Ride height at the axle
——-0.18 inSpeedometer reading
——-1.07% over-read
| Dimension | 255/80R17 | 285/70R17 | Change |
|---|---|---|---|
| Overall diameter | 33.06 in | 32.71 in | -0.35 in (-1.07%) |
| Section width | 10.04 in / 255 mm | 11.22 in / 285 mm | +1.18 in (+11.76%) |
| Sidewall height | 8.03 in | 7.85 in | -0.18 in |
| Circumference | 103.9 in | 102.8 in | -1.1 in |
| Revolutions per mile | 610.0 | 616.6 | +6.6 |
| Ride height at the axle | — | — | -0.18 in |
| Speedometer reading | — | — | -1.07% over-read |
Calibrated for 255/80R17, running 285/70R17
- Dial reads 30
- 29.7 mph
- Dial reads 50
- 49.5 mph
- Dial reads 70
- 69.2 mph
- Odometer counts 100
- 98.9 mi covered
Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.
The narrower tire here is the taller one. That is the whole reason the pairing is worth measuring.
Two shapes, one height
- 255/80R17 — a 10.04 in casing with an 8.03 in sidewall, reaching 33.06 in
- 285/70R17 — an 11.22 in casing with a 7.85 in sidewall, reaching 32.71 in
An 80-series profile is what allows a narrow casing to get this tall. Eighty per cent of 255 mm is more sidewall than seventy per cent of 285 mm, despite the second casing being 30 mm wider, and the result is 0.35 in in the narrow tire's favour.
What the 30 mm buys and costs
The wide size has 1.18 in more section width — 11.76% — and gives up a third of an inch of height for it. Which of those matters depends entirely on what the vehicle runs out of first, and the two dimensions are constrained by completely different parts of it.
For anyone whose limit is width at full lock, the 255/80R17 delivers more diameter in less space than anything else commonly available on a 17-inch wheel.
The instrument difference is negligible
1.07%, and the direction is the unusual one: a speedometer set up for the narrow tire reads high on the wide one. Two inches of extra casing and the vehicle ends up going marginally slower than the needle claims — a reminder that width contributes nothing to the reading and the 80-series sidewall contributes everything.
Why 80-series sizes are rare now
Because the market moved to larger wheels, and a tall profile on a large wheel produces a tire nobody can package. 255/80R17 survives because it is the narrow-and-tall answer for trucks that need diameter without track width — an expedition and utility niche rather than a mainstream one — and because nothing else does the job.
Availability reflects that. The tread list in 255/80R17 is short and specialised, while 285/70R17 is among the most heavily stocked light-truck sizes in North America.
The sidewall proportions, stated
Divide sidewall by width and the difference in character is obvious: the narrow tire's sidewall is four-fifths of its casing width, the wide tire's is seven-tenths. That is a genuinely different shape, not a scaled version of the same one, and it shows in how each tire deforms when pressure is lowered — an effect this site does not attempt to quantify but which follows directly from the proportions above.
The 16-inch version of the same idea
235/85R16 against 285/75R16 is the same narrow-versus-wide comparison one wheel size down, with an even taller profile and a wider gap between the two casings.