215/60R21 vs 225/55R21
Going from one to the other changes the overall height by -1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/60R21 | 225/55R21 | Change |
|---|---|---|---|
| Overall height | 31.2" | 30.7" | -1.3 % |
| Sidewall | 5.08" | 4.87" | -4.1 % |
| Section width | 215 mm | 225 mm | +4.7 % |
| Circumference | 97.9" | 96.6" | -1.3 % |
| Revs per mile | 647 | 656 | +1.3 % |
| Axle height | 15.58" | 15.37" | -5.3 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 215/60R21. Fit 225/55R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.1 mph | -0.9 |
| 90 mph | 88.8 mph | -1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,867 on the road, so it over-counts by 133. At a true 70 mph the first turns 755 times a minute, the second 765.