275/70R24.5 vs 285/70R24.5
Going from one to the other changes the overall height by +1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/70R24.5 | 285/70R24.5 | Change |
|---|---|---|---|
| Overall height | 39.7" | 40.2" | +1.4 % |
| Sidewall | 7.58" | 7.85" | +3.6 % |
| Section width | 275 mm | 285 mm | +3.6 % |
| Circumference | 124.6" | 126.3" | +1.4 % |
| Revs per mile | 509 | 502 | -1.4 % |
| Axle height | 19.83" | 20.10" | +7.0 mm |
| Approved rim width | 7.5–10" | 8–10.5" | overlap 8–10" |
Both are approved on a rim 8" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 275/70R24.5. Fit 285/70R24.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.3 mph | +1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,139 on the road, so it under-counts by 139. At a true 70 mph the first turns 593 times a minute, the second 585.