285/50R20 vs 265/55R20
New overall diameter
31.48″
was 31.22″
True speed at an indicated 60
60.5 mph
speedometer reads low
Revolutions per mile
641
was 646 · −5
Switching from 285/50R20 to 265/55R20? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 285/50R20 | 265/55R20 | Change |
|---|---|---|---|
| Overall diameter | 31.22″ | 31.48″ | +0.26″ (+0.8%) |
| Sidewall height | 5.61″ (142.5 mm) | 5.74″ (145.8 mm) | +3.3 mm |
| Tread width | 285 mm | 265 mm | −20 mm |
| Circumference | 98.08″ | 98.89″ | +0.80″ |
| Revs per mile | 646 | 641 | −5 |
| Speedometer error | baseline | +0.8% | reads low |
Diameter overlay
285/50R20 265/55R20
Speedometer check
With 265/55R20 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
25.2 mph actual
35 mph shown
35.3 mph actual
45 mph shown
45.4 mph actual
55 mph shown
55.5 mph actual
65 mph shown
65.5 mph actual
75 mph shown
75.6 mph actual
Common questions
- Will 265/55R20 fit instead of 285/50R20?
- Good fit. Within the 3% rule — overall diameter changes only 0.8%. Speedometer calibration, ABS, traction control and gearing all stay in their intended range. Your speedometer will read lower than your true speed. Overall diameter goes from 31.22″ to 31.48″, a change of +0.8%. 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 265/55R20?
- At an indicated 60 mph you would actually be travelling about 60.5 mph — a +0.8% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 285/50R20 and 265/55R20?
- 285/50R20 turns roughly 646 revolutions per mile; 265/55R20 turns roughly 641. That is a change of −5 revolutions per mile, which is what shifts odometer and speedometer readings.