275/65R18 vs 285/60R18
New overall diameter
31.46″
was 32.07″
True speed at an indicated 60
58.9 mph
your speedo reads high
Revolutions per mile
641
was 629, +12
| Measurement | 275/65R18 | 285/60R18 | Change |
|---|---|---|---|
| Overall diameter | 32.07″ | 31.46″ | −0.61″ (−1.9%) |
| Sidewall height | 7.04″ (178.8 mm) | 6.73″ (171.0 mm) | −7.8 mm |
| Tread width | 275 mm | 285 mm | +10 mm |
| Circumference | 100.77″ | 98.85″ | −1.92″ |
| Revs per mile | 629 | 641 | +12 |
| Speedometer error | baseline | −1.9% | reads high |
Diameter overlay
275/65R18 285/60R18
Speedometer check
With 285/60R18 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
24.5 mph actual
35 mph shown
34.3 mph actual
45 mph shown
44.1 mph actual
55 mph shown
54.0 mph actual
65 mph shown
63.8 mph actual
75 mph shown
73.6 mph actual
Common questions
- Will 285/60R18 fit instead of 275/65R18?
- Diameter moves 1.9%, comfortably inside the 3% rule. Your speedometer, ABS, traction control and gearing all stay in the range they were calibrated for. Your speedometer will read high, so you are going slower than it says. Overall diameter goes from 32.07″ to 31.46″, a change of −1.9%. 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 285/60R18?
- At an indicated 60 mph you are really doing about 58.9 mph, a −1.9% error. The speedometer reads high, so you are going slower than it shows.
- What is the difference in revolutions per mile between 275/65R18 and 285/60R18?
- 275/65R18 turns about 629 times per mile and 285/60R18 turns about 641, a difference of +12. Your speedometer and odometer both count rotations, so this number is what throws them off.