225/65R20 vs 215/70R20
Going from one to the other changes the overall height by +1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/65R20 | 215/70R20 | Change |
|---|---|---|---|
| Overall height | 31.5" | 31.9" | +1.1 % |
| Sidewall | 5.76" | 5.93" | +2.9 % |
| Section width | 225 mm | 215 mm | -4.4 % |
| Circumference | 99.0" | 100.1" | +1.1 % |
| Revs per mile | 640 | 633 | -1.1 % |
| Axle height | 15.76" | 15.93" | +4.3 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 225/65R20. Fit 215/70R20 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 | 91.0 mph | +1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,106 on the road, so it under-counts by 106. At a true 70 mph the first turns 747 times a minute, the second 739.