235/60R22 vs 255/60R22
Going from one to the other changes the overall height by +2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 235/60R22 | 255/60R22 | Change |
|---|---|---|---|
| Overall height | 33.1" | 34.0" | +2.9 % |
| Sidewall | 5.55" | 6.02" | +8.5 % |
| Section width | 235 mm | 255 mm | +8.5 % |
| Circumference | 104.0" | 107.0" | +2.9 % |
| Revs per mile | 609 | 592 | -2.9 % |
| Axle height | 16.55" | 17.02" | +12.0 mm |
| Approved rim width | 6.5–8.5" | 7–9.5" | overlap 7–8.5" |
Both are approved on a rim 7" to 8.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 235/60R22. Fit 255/60R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.6 mph | +2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,285 on the road, so it under-counts by 285. At a true 70 mph the first turns 711 times a minute, the second 691.