255/55R20 vs 265/60R20
New overall diameter
32.52″
was 31.04″
True speed at an indicated 60
62.9 mph
speedometer reads low
Revolutions per mile
620
was 650 · −29
Switching from 255/55R20 to 265/60R20? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 255/55R20 | 265/60R20 | Change |
|---|---|---|---|
| Overall diameter | 31.04″ | 32.52″ | +1.48″ (+4.8%) |
| Sidewall height | 5.52″ (140.3 mm) | 6.26″ (159.0 mm) | +18.8 mm |
| Tread width | 255 mm | 265 mm | +10 mm |
| Circumference | 97.53″ | 102.16″ | +4.64″ |
| Revs per mile | 650 | 620 | −29 |
| Speedometer error | baseline | +4.8% | reads low |
Diameter overlay
255/55R20 265/60R20
Speedometer check
With 265/60R20 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
26.2 mph actual
35 mph shown
36.7 mph actual
45 mph shown
47.1 mph actual
55 mph shown
57.6 mph actual
65 mph shown
68.1 mph actual
75 mph shown
78.6 mph actual
Common questions
- Will 265/60R20 fit instead of 255/55R20?
- Marginal fit — proceed with care. The 4.8% diameter change is between 3% and 5%. It can work, but expect noticeable speedometer error and check wheel-well clearance, scrub radius and gearing before committing. Your speedometer will read lower than your true speed. Overall diameter goes from 31.04″ to 32.52″, a change of +4.8%. 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 265/60R20?
- At an indicated 60 mph you would actually be travelling about 62.9 mph — a +4.8% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 255/55R20 and 265/60R20?
- 255/55R20 turns roughly 650 revolutions per mile; 265/60R20 turns roughly 620. That is a change of −29 revolutions per mile, which is what shifts odometer and speedometer readings.