255/50R16 vs 245/55R16
Going from one to the other changes the overall height by +2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/50R16 | 245/55R16 | Change |
|---|---|---|---|
| Overall height | 26.0" | 26.6" | +2.2 % |
| Sidewall | 5.02" | 5.31" | +5.7 % |
| Section width | 255 mm | 245 mm | -3.9 % |
| Circumference | 81.8" | 83.6" | +2.2 % |
| Revs per mile | 775 | 758 | -2.2 % |
| Axle height | 13.02" | 13.31" | +7.3 mm |
| Approved rim width | 7–9.5" | 7–9" | 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 255/50R16. Fit 245/55R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.5 mph | +1.5 |
| 90 mph | 92.0 mph | +2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,219 on the road, so it under-counts by 219. At a true 70 mph the first turns 904 times a minute, the second 884.