225/55R21 vs 215/60R21
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 | 225/55R21 | 215/60R21 | Change |
|---|---|---|---|
| Overall height | 30.7" | 31.2" | +1.3 % |
| Sidewall | 4.87" | 5.08" | +4.2 % |
| Section width | 225 mm | 215 mm | -4.4 % |
| Circumference | 96.6" | 97.9" | +1.3 % |
| Revs per mile | 656 | 647 | -1.3 % |
| Axle height | 15.37" | 15.58" | +5.3 mm |
| Approved rim width | 6–8.5" | 6–8" | 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 225/55R21. Fit 215/60R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 70.9 mph | +0.9 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,134 on the road, so it under-counts by 134. At a true 70 mph the first turns 765 times a minute, the second 755.