215/65R21 vs 215/70R21
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/65R21 | 215/70R21 | Change |
|---|---|---|---|
| Overall height | 32.0" | 32.9" | +2.6 % |
| Sidewall | 5.50" | 5.93" | +7.7 % |
| Section width | 215 mm | 215 mm | 0.0 % |
| Circumference | 100.5" | 103.2" | +2.6 % |
| Revs per mile | 630 | 614 | -2.6 % |
| Axle height | 16.00" | 16.43" | +10.8 mm |
| Approved rim width | 6–8" | 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 215/65R21. Fit 215/70R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.9 mph | +1.9 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,264 on the road, so it under-counts by 264. At a true 70 mph the first turns 735 times a minute, the second 716.