245/55R16 vs 255/50R16
Going from one to the other changes the overall height by -2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/55R16 | 255/50R16 | Change |
|---|---|---|---|
| Overall height | 26.6" | 26.0" | -2.1 % |
| Sidewall | 5.31" | 5.02" | -5.4 % |
| Section width | 245 mm | 255 mm | +4.1 % |
| Circumference | 83.6" | 81.8" | -2.1 % |
| Revs per mile | 758 | 775 | +2.1 % |
| Axle height | 13.31" | 13.02" | -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 245/55R16. Fit 255/50R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.5 mph | -1.5 |
| 90 mph | 88.1 mph | -1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,785 on the road, so it over-counts by 215. At a true 70 mph the first turns 884 times a minute, the second 904.