285/60R18 vs 265/55R20
New overall diameter
31.48″
was 31.46″
True speed at an indicated 60
60.0 mph
no meaningful change
Revolutions per mile
641
was 641, −0
| Measurement | 285/60R18 | 265/55R20 | Change |
|---|---|---|---|
| Overall diameter | 31.46″ | 31.48″ | +0.01″ (+0.0%) |
| Sidewall height | 6.73″ (171.0 mm) | 5.74″ (145.8 mm) | −25.3 mm |
| Tread width | 285 mm | 265 mm | −20 mm |
| Circumference | 98.85″ | 98.89″ | +0.04″ |
| Revs per mile | 641 | 641 | −0 |
| Speedometer error | baseline | +0.0% | no change |
Diameter overlay
285/60R18 265/55R20
Speedometer check
With 265/55R20 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
25.0 mph actual
35 mph shown
35.0 mph actual
45 mph shown
45.0 mph actual
55 mph shown
55.0 mph actual
65 mph shown
65.0 mph actual
75 mph shown
75.0 mph actual
Common questions
- Will 265/55R20 fit instead of 285/60R18?
- Diameter moves 0.0%, comfortably inside the 3% rule. Your speedometer, ABS, traction control and gearing all stay in the range they were calibrated for. Your speedometer stays accurate. Overall diameter goes from 31.46″ to 31.48″, a change of +0.0%. The rule of thumb most shops use: under 3% is fine, 3 to 5% needs a clearance check, over 5% needs recalibration.
- How far off will my speedometer read on 265/55R20?
- At an indicated 60 mph you are really doing about 60.0 mph, a +0.0% error. That is effectively no change.
- What is the difference in revolutions per mile between 285/60R18 and 265/55R20?
- 285/60R18 turns about 641 times per mile and 265/55R20 turns about 641, a difference of −0. Your speedometer and odometer both count rotations, so this number is what throws them off.