245/55R22 vs 255/50R22
Going from one to the other changes the overall height by -1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/55R22 | 255/50R22 | Change |
|---|---|---|---|
| Overall height | 32.6" | 32.0" | -1.8 % |
| Sidewall | 5.31" | 5.02" | -5.4 % |
| Section width | 245 mm | 255 mm | +4.1 % |
| Circumference | 102.4" | 100.7" | -1.8 % |
| Revs per mile | 618 | 629 | +1.8 % |
| Axle height | 16.31" | 16.02" | -7.3 mm |
| Approved rim width | 7–9" | 7–9.5" | overlap 7–9" |
Both are approved on a rim 7" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 245/55R22. Fit 255/50R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.4 mph | -1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,825 on the road, so it over-counts by 175. At a true 70 mph the first turns 722 times a minute, the second 734.