255/50R24 vs 255/55R24
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 | 255/50R24 | 255/55R24 | Change |
|---|---|---|---|
| Overall height | 34.0" | 35.0" | +2.9 % |
| Sidewall | 5.02" | 5.52" | +10.0 % |
| Section width | 255 mm | 255 mm | 0.0 % |
| Circumference | 106.9" | 110.1" | +2.9 % |
| Revs per mile | 592 | 576 | -2.9 % |
| Axle height | 17.02" | 17.52" | +12.8 mm |
| Approved rim width | 7–9.5" | 7–9.5" | overlap 7–9.5" |
Both are approved on a rim 7" 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 255/50R24. Fit 255/55R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.5 mph | +1.5 |
| 70 mph | 72.1 mph | +2.1 |
| 90 mph | 92.7 mph | +2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,295 on the road, so it under-counts by 295. At a true 70 mph the first turns 691 times a minute, the second 671.