255/60R19 vs 285/50R20
New overall diameter
31.22″
was 31.05″
True speed at an indicated 60
60.3 mph
your speedo reads low
Revolutions per mile
646
was 650, −4
| Measurement | 255/60R19 | 285/50R20 | Change |
|---|---|---|---|
| Overall diameter | 31.05″ | 31.22″ | +0.17″ (+0.6%) |
| Sidewall height | 6.02″ (153.0 mm) | 5.61″ (142.5 mm) | −10.5 mm |
| Tread width | 255 mm | 285 mm | +30 mm |
| Circumference | 97.54″ | 98.08″ | +0.54″ |
| Revs per mile | 650 | 646 | −4 |
| Speedometer error | baseline | +0.6% | reads low |
Diameter overlay
255/60R19 285/50R20
Speedometer check
With 285/50R20 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
25.1 mph actual
35 mph shown
35.2 mph actual
45 mph shown
45.3 mph actual
55 mph shown
55.3 mph actual
65 mph shown
65.4 mph actual
75 mph shown
75.4 mph actual
Common questions
- Will 285/50R20 fit instead of 255/60R19?
- Overall diameter changes 0.6%; section width changes 30 mm. Diameter comparison alone cannot confirm fitment. Verify the vehicle maker's approved rim width, tire load and speed ratings, and clearance at full steering lock and suspension compression. Confirm any possible ABS, traction-control, speedometer, and drivetrain effects with the vehicle maker or a qualified tire professional. Overall diameter goes from 31.05″ to 31.22″, a change of +0.6%. 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 285/50R20?
- At an indicated 60 mph you are really doing about 60.3 mph, a +0.6% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 255/60R19 and 285/50R20?
- 255/60R19 turns about 650 times per mile and 285/50R20 turns about 646, a difference of −4. Your speedometer and odometer both count rotations, so this number is what throws them off.