265/60R18 vs 275/70R17 — the smaller wheel, the taller tire
A Tacoma wheel-and-tire change that runs against intuition, and where plus-sizing arithmetic is easiest to get backwards.
275/70R17 is 1.64 in taller than 265/60R18 (5.37%) and 0.39 in wider. A speedometer calibrated for 265/60R18 would under-read by 5.37%.
Measured against each other
Overall diameter
30.52 in32.16 in+1.64 in (+5.37%)Section width
10.43 in / 265 mm10.83 in / 275 mm+0.39 in (+3.77%)Sidewall height
6.26 in7.58 in+1.32 inCircumference
95.9 in101.0 in+5.1 inRevolutions per mile
660.8627.2-33.7Ride height at the axle
——+0.82 inSpeedometer reading
——+5.37% under-read
| Dimension | 265/60R18 | 275/70R17 | Change |
|---|---|---|---|
| Overall diameter | 30.52 in | 32.16 in | +1.64 in (+5.37%) |
| Section width | 10.43 in / 265 mm | 10.83 in / 275 mm | +0.39 in (+3.77%) |
| Sidewall height | 6.26 in | 7.58 in | +1.32 in |
| Circumference | 95.9 in | 101.0 in | +5.1 in |
| Revolutions per mile | 660.8 | 627.2 | -33.7 |
| Ride height at the axle | — | — | +0.82 in |
| Speedometer reading | — | — | +5.37% under-read |
Calibrated for 265/60R18, running 275/70R17
- Dial reads 30
- 31.6 mph
- Dial reads 50
- 52.7 mph
- Dial reads 70
- 73.8 mph
- Odometer counts 100
- 105.4 mi covered
Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.
Going down a wheel size and up in tire size at the same time is where most people's mental arithmetic fails. The 17-inch assembly here is the bigger one by a comfortable margin.
Two changes in opposite directions
The wheel loses an inch, which on its own would take an inch off the diameter. The tire gains ten points of aspect ratio and 10 mm of width, which together add far more than that back.
- Sidewall: 6.26 in to 7.58 in — 1.32 in more
- Wheel: 18 in to 17 in — 1.00 in less
- Diameter: 30.52 in to 32.16 in — 1.64 in more
Two sidewalls at +1.32 in each is +2.64 in, less the inch the wheel gave up, which leaves 1.64 in.
Why the axle only rises 0.82 in
Because ride height at the axle is always half the diameter change, regardless of what the wheel is doing. Half of 1.64 in is 0.82 in, and the smaller wheel does not alter that: the axle centre is determined by the outside of the tire, not by the rim.
This is precisely the point at which plus-sizing arithmetic gets confusing, because two of the three numbers move in one direction and the third moves in the other.
The readings
5.37% reaches the driver as a dial reading of 60 against a road speed of 63.2, and as an odometer running about five and a half miles short in every hundred.
What the sidewall is worth
Over an inch and a quarter more rubber between the rim and the road, on the same truck. That is the substantive reason people move from the 18-inch package to the 17-inch one, and it is entirely invisible in a comparison of diameters — two assemblies could match on height and still differ by this much in sidewall.
Section width barely participates: 10.43 in to 10.83 in, 0.39 in, 3.77%.
The other 17-inch option
265/60R18 against 285/70R17 makes the same wheel change with a wider, taller tire — 2.19 in rather than 1.64 in — and is the version of this comparison most often asked about on the off-road trims.