275/65R18 vs 285/75R18 — a 35 without changing wheels
The second-generation Tundra's route to a 35-inch tire, and the rare case where the metric size is the taller option.
285/75R18 is 2.76 in taller than 275/65R18 (8.59%) and 0.39 in wider. A speedometer calibrated for 275/65R18 would under-read by 8.59%.
Measured against each other
Overall diameter
32.07 in34.83 in+2.76 in (+8.59%)Section width
10.83 in / 275 mm11.22 in / 285 mm+0.39 in (+3.64%)Sidewall height
7.04 in8.42 in+1.38 inCircumference
100.8 in109.4 in+8.7 inRevolutions per mile
628.8579.0-49.8Ride height at the axle
——+1.38 inSpeedometer reading
——+8.59% under-read
| Dimension | 275/65R18 | 285/75R18 | Change |
|---|---|---|---|
| Overall diameter | 32.07 in | 34.83 in | +2.76 in (+8.59%) |
| Section width | 10.83 in / 275 mm | 11.22 in / 285 mm | +0.39 in (+3.64%) |
| Sidewall height | 7.04 in | 8.42 in | +1.38 in |
| Circumference | 100.8 in | 109.4 in | +8.7 in |
| Revolutions per mile | 628.8 | 579.0 | -49.8 |
| Ride height at the axle | — | — | +1.38 in |
| Speedometer reading | — | — | +8.59% under-read |
Calibrated for 275/65R18, running 285/75R18
- Dial reads 30
- 32.6 mph
- Dial reads 50
- 54.3 mph
- Dial reads 70
- 76.0 mph
- Odometer counts 100
- 108.6 mi covered
Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.
34.83 in is a 35 by any reasonable rounding, reached without a flotation size, without a wheel change and with an 8.42 in sidewall intact.
The profile does the work
Ten points of aspect ratio, from 65 to 75, plus 10 mm of width. Sidewall goes from 7.04 in to 8.42 in — 1.38 in, nearly all of it from the profile — and doubled that produces the 2.76 in of extra diameter.
Section width moves only 0.39 in, from 10.83 in to 11.22 in. So this is a height change with almost no lateral component, which is unusual for a step of this size.
The instrument arithmetic
1,086 miles are covered for every 1,000 the odometer records. Over a warranty period or a lease allowance that is the figure with money attached to it, and it is the one worth writing down. The speedometer error in the panel above is the same quantity, and it is merely the version you notice.
A 3.73:1 axle converts to 4.05:1, and 4.10:1 is the closest set sold. This is the magnitude at which owners start discussing whether to bother.
Why 285/75R18 is unusual
Because 75-series sizes on 18-inch wheels are not common — the industry mostly went to shorter profiles as wheels grew. This size survives because it serves exactly this purpose: a 35-inch class tire for trucks delivered on 18s whose owners do not want a flotation size or a new set of wheels.
The tread list is correspondingly short and weighted toward all-terrain and rugged patterns.
Where it beats the 20-inch route
275/65R18 against 285/65R20 reaches 34.59 in — a quarter of an inch shorter than this — by buying two inches of wheel. This page reaches further with the wheels already on the truck, and keeps 1.12 in more sidewall while doing it. On height alone, the metric 18-inch route wins.
The name it gets
34.83 in rounds to 35, and that is how the size is discussed. It is also 0.17 in short of a genuine 35x12.50, which is the same order of shortfall as most metric approximations of a round number manage. Anyone pricing a set against flotation 35s should know they are quoting a tire a sixth of an inch shorter and 1.28 in narrower.
What has to be checked on the truck
Whether 2.76 in of extra diameter clears at full compression and full lock, and whether the tire in front of you meets the rating the placard demands. Neither follows from a size code.