265/50R20 vs 285/50R20
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/50R20 | 285/50R20 | Change |
|---|---|---|---|
| Overall height | 30.4" | 31.2" | +2.6 % |
| Sidewall | 5.22" | 5.61" | +7.5 % |
| Section width | 265 mm | 285 mm | +7.5 % |
| Circumference | 95.6" | 98.1" | +2.6 % |
| Revs per mile | 663 | 646 | -2.6 % |
| Axle height | 15.22" | 15.61" | +10.0 mm |
| Approved rim width | 7.5–9.5" | 8–10.5" | overlap 8–9.5" |
Both are approved on a rim 8" to 9.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 265/50R20. Fit 285/50R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,259 on the road, so it under-counts by 259. At a true 70 mph the first turns 773 times a minute, the second 754.