265/60R20 vs 285/50R20
New overall diameter
31.22″
was 32.52″
True speed at an indicated 60
57.6 mph
your speedo reads high
Revolutions per mile
646
was 620, +26
| Measurement | 265/60R20 | 285/50R20 | Change |
|---|---|---|---|
| Overall diameter | 32.52″ | 31.22″ | −1.30″ (−4.0%) |
| Sidewall height | 6.26″ (159.0 mm) | 5.61″ (142.5 mm) | −16.5 mm |
| Tread width | 265 mm | 285 mm | +20 mm |
| Circumference | 102.16″ | 98.08″ | −4.08″ |
| Revs per mile | 620 | 646 | +26 |
| Speedometer error | baseline | −4.0% | reads high |
Diameter overlay
265/60R20 285/50R20
Speedometer check
With 285/50R20 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
24.0 mph actual
35 mph shown
33.6 mph actual
45 mph shown
43.2 mph actual
55 mph shown
52.8 mph actual
65 mph shown
62.4 mph actual
75 mph shown
72.0 mph actual
Common questions
- Will 285/50R20 fit instead of 265/60R20?
- At 4.0% this lands between the 3% and 5% marks. Plenty of people run swaps like this, but you will see real speedometer error, and you want to check the wheel well at full lock and full compression before you buy. Your speedometer will read high, so you are going slower than it says. Overall diameter goes from 32.52″ to 31.22″, a change of −4.0%. 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 285/50R20?
- At an indicated 60 mph you are really doing about 57.6 mph, a −4.0% error. The speedometer reads high, so you are going slower than it shows.
- What is the difference in revolutions per mile between 265/60R20 and 285/50R20?
- 265/60R20 turns about 620 times per mile and 285/50R20 turns about 646, a difference of +26. Your speedometer and odometer both count rotations, so this number is what throws them off.