275/55R20 vs 275/60R20 — one profile step, nothing else
The smallest change this site can draw with any clarity, and the reference case for what a single aspect step is worth on a wide casing.
275/60R20 is 1.08 in taller than 275/55R20 (3.39%) and 0.00 in wider. A speedometer calibrated for 275/55R20 would under-read by 3.39%.
Measured against each other
Overall diameter
31.91 in32.99 in+1.08 in (+3.39%)Section width
10.83 in / 275 mm10.83 in / 275 mm0.00 in (0.00%)Sidewall height
5.95 in6.50 in+0.54 inCircumference
100.2 in103.6 in+3.4 inRevolutions per mile
632.0611.3-20.7Ride height at the axle
——+0.54 inSpeedometer reading
——+3.39% under-read
| Dimension | 275/55R20 | 275/60R20 | Change |
|---|---|---|---|
| Overall diameter | 31.91 in | 32.99 in | +1.08 in (+3.39%) |
| Section width | 10.83 in / 275 mm | 10.83 in / 275 mm | 0.00 in (0.00%) |
| Sidewall height | 5.95 in | 6.50 in | +0.54 in |
| Circumference | 100.2 in | 103.6 in | +3.4 in |
| Revolutions per mile | 632.0 | 611.3 | -20.7 |
| Ride height at the axle | — | — | +0.54 in |
| Speedometer reading | — | — | +3.39% under-read |
Calibrated for 275/55R20, running 275/60R20
- Dial reads 30
- 31.0 mph
- Dial reads 50
- 51.7 mph
- Dial reads 70
- 72.4 mph
- Odometer counts 100
- 103.4 mi covered
Change either size in the comparison tool, or see the full speed table in the speedometer error calculator.
Two sizes that differ by one character. Everything else about the code, and about the space the tire occupies laterally, is identical.
What five points is worth on a 275
5.95 in of sidewall becomes 6.50 in — 0.54 in more, which is five per cent of 275 mm doubled and converted. The section width does not change, at 10.83 in in both cases, and the wheel does not change either.
The result is 1.08 in of extra diameter, or 3.39%, and it arrives with nothing else attached to it.
Why this is the useful reference
Because nothing is confounded. Every other comparison at this wheel size involves either a width change, a wheel change, or a notation change. Here the only moving part is the profile, so the 1.08 in is attributable to it entirely and can be used as a yardstick for reading other pairings.
The general rule it demonstrates: on a 275 mm casing, one five-point aspect step is worth just over an inch of overall diameter. Wider casings gain more from the same nominal step and narrower ones gain less, because the step is a percentage rather than a length.
The consequences
3.39%, felt as 62.0 mph at a dial reading of 60. Since the wheel and the casing are both fixed, that percentage and the sidewall gain are the only two things on the whole page that changed at all.
The name that changes
32.99 in rounds to 33, and 275/60R20 is consequently described as a 33 by most retailers. 275/55R20, at 31.91 in, rounds to 32. So a single character in the size code moves the tire across the boundary between two conversational categories, which is a much bigger change in how the tire is discussed than in how tall it is.
Both sizes are original equipment
Neither is an aftermarket specification. Full-size half-tons are delivered on both, depending on trim and on which tire the manufacturer specified for the load rating it needed. So a buyer comparing two trucks with 20-inch wheels may well be comparing exactly these two sizes, with a 1.08 in difference in how tall each one stands and no difference at all in how much room the tire needs beside it.
What follows on the same wheel
The next real step up is 285/65R20 at 34.59 in, which moves both variables at once and adds another 1.59 in.