215/35R21 vs 225/35R21
Going from one to the other changes the overall height by +1.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/35R21 | 225/35R21 | Change |
|---|---|---|---|
| Overall height | 26.9" | 27.2" | +1.0 % |
| Sidewall | 2.96" | 3.10" | +4.7 % |
| Section width | 215 mm | 225 mm | +4.7 % |
| Circumference | 84.6" | 85.5" | +1.0 % |
| Revs per mile | 749 | 741 | -1.0 % |
| Axle height | 13.46" | 13.60" | +3.5 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 215/35R21. Fit 225/35R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.5 mph | +0.5 |
| 70 mph | 70.7 mph | +0.7 |
| 90 mph | 90.9 mph | +0.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,102 on the road, so it under-counts by 102. At a true 70 mph the first turns 874 times a minute, the second 865.