275/55R20 vs 285/65R20
New overall diameter
34.59″
was 31.91″
True speed at an indicated 60
65.0 mph
your speedo reads low
Revolutions per mile
583
was 632, −49
| Measurement | 275/55R20 | 285/65R20 | Change |
|---|---|---|---|
| Overall diameter | 31.91″ | 34.59″ | +2.68″ (+8.4%) |
| Sidewall height | 5.95″ (151.3 mm) | 7.29″ (185.3 mm) | +34.0 mm |
| Tread width | 275 mm | 285 mm | +10 mm |
| Circumference | 100.25″ | 108.66″ | +8.41″ |
| Revs per mile | 632 | 583 | −49 |
| Speedometer error | baseline | +8.4% | reads low |
Diameter overlay
275/55R20 285/65R20
Speedometer check
With 285/65R20 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
27.1 mph actual
35 mph shown
37.9 mph actual
45 mph shown
48.8 mph actual
55 mph shown
59.6 mph actual
65 mph shown
70.5 mph actual
75 mph shown
81.3 mph actual
Common questions
- Will 285/65R20 fit instead of 275/55R20?
- 8.4% is past the 5% mark, which is where this stops being a tire choice and starts being a project. Expect rubbing, meaningful speedometer error, and extra load on ABS, stability control and the drivetrain. Recalibration is the usual fix. Your speedometer will read low, so you are going faster than it says. Overall diameter goes from 31.91″ to 34.59″, a change of +8.4%. 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 285/65R20?
- At an indicated 60 mph you are really doing about 65.0 mph, a +8.4% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 275/55R20 and 285/65R20?
- 275/55R20 turns about 632 times per mile and 285/65R20 turns about 583, a difference of −49. Your speedometer and odometer both count rotations, so this number is what throws them off.