275/70R17 vs 255/75R17
New overall diameter
32.06″
was 32.16″
True speed at an indicated 60
59.8 mph
speedometer reads high
Revolutions per mile
629
was 627 · +2
Switching from 275/70R17 to 255/75R17? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 275/70R17 | 255/75R17 | Change |
|---|---|---|---|
| Overall diameter | 32.16″ | 32.06″ | −0.10″ (−0.3%) |
| Sidewall height | 7.58″ (192.5 mm) | 7.53″ (191.3 mm) | −1.3 mm |
| Tread width | 275 mm | 255 mm | −20 mm |
| Circumference | 101.03″ | 100.72″ | −0.31″ |
| Revs per mile | 627 | 629 | +2 |
| Speedometer error | baseline | −0.3% | reads high |
Diameter overlay
275/70R17 255/75R17
Speedometer check
With 255/75R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
24.9 mph actual
35 mph shown
34.9 mph actual
45 mph shown
44.9 mph actual
55 mph shown
54.8 mph actual
65 mph shown
64.8 mph actual
75 mph shown
74.8 mph actual
Common questions
- Will 255/75R17 fit instead of 275/70R17?
- Good fit. Within the 3% rule — overall diameter changes only 0.3%. Speedometer calibration, ABS, traction control and gearing all stay in their intended range. Your speedometer will read higher than your true speed. Overall diameter goes from 32.16″ to 32.06″, a change of −0.3%. As a rule of thumb, under 3% is safe, 3–5% needs a clearance check, and over 5% is not recommended.
- How far off will my speedometer read on 255/75R17?
- At an indicated 60 mph you would actually be travelling about 59.8 mph — a −0.3% error. The speedometer reads high, so you are going slower than it shows.
- What is the difference in revolutions per mile between 275/70R17 and 255/75R17?
- 275/70R17 turns roughly 627 revolutions per mile; 255/75R17 turns roughly 629. That is a change of +2 revolutions per mile, which is what shifts odometer and speedometer readings.