245/50R15 vs 225/55R15
Going from one to the other changes the overall height by +0.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/50R15 | 225/55R15 | Change |
|---|---|---|---|
| Overall height | 24.6" | 24.7" | +0.4 % |
| Sidewall | 4.82" | 4.87" | +1.0 % |
| Section width | 245 mm | 225 mm | -8.2 % |
| Circumference | 77.4" | 77.7" | +0.4 % |
| Revs per mile | 818 | 815 | -0.4 % |
| Axle height | 12.32" | 12.37" | +1.3 mm |
| Approved rim width | 7–9" | 6–8.5" | 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 245/50R15. Fit 225/55R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.2 mph | +0.2 |
| 70 mph | 70.3 mph | +0.3 |
| 90 mph | 90.4 mph | +0.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,040 on the road, so it under-counts by 40. At a true 70 mph the first turns 955 times a minute, the second 951.