225/65R21 vs 245/60R21
Going from one to the other changes the overall height by +0.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/65R21 | 245/60R21 | Change |
|---|---|---|---|
| Overall height | 32.5" | 32.6" | +0.2 % |
| Sidewall | 5.76" | 5.79" | +0.5 % |
| Section width | 225 mm | 245 mm | +8.9 % |
| Circumference | 102.2" | 102.3" | +0.2 % |
| Revs per mile | 620 | 619 | -0.2 % |
| Axle height | 16.26" | 16.29" | +0.8 mm |
| Approved rim width | 6–8.5" | 7–9" | 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 225/65R21. Fit 245/60R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.1 mph | +0.1 |
| 70 mph | 70.1 mph | +0.1 |
| 90 mph | 90.2 mph | +0.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,018 on the road, so it under-counts by 18. At a true 70 mph the first turns 724 times a minute, the second 722.