215/55R20 vs 225/50R20
Going from one to the other changes the overall height by -1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/55R20 | 225/50R20 | Change |
|---|---|---|---|
| Overall height | 29.3" | 28.9" | -1.5 % |
| Sidewall | 4.66" | 4.43" | -4.9 % |
| Section width | 215 mm | 225 mm | +4.7 % |
| Circumference | 92.1" | 90.7" | -1.5 % |
| Revs per mile | 688 | 699 | +1.5 % |
| Axle height | 14.66" | 14.43" | -5.8 mm |
| Approved rim width | 6–8" | 6–8.5" | overlap 6–8" |
Both are approved on a rim 6" to 8" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 215/55R20. Fit 225/50R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.9 mph | -1.1 |
| 90 mph | 88.6 mph | -1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,846 on the road, so it over-counts by 154. At a true 70 mph the first turns 803 times a minute, the second 815.