205/75R20 vs 215/70R20
Going from one to the other changes the overall height by -0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/75R20 | 215/70R20 | Change |
|---|---|---|---|
| Overall height | 32.1" | 31.9" | -0.8 % |
| Sidewall | 6.05" | 5.93" | -2.1 % |
| Section width | 205 mm | 215 mm | +4.9 % |
| Circumference | 100.9" | 100.1" | -0.8 % |
| Revs per mile | 628 | 633 | +0.8 % |
| Axle height | 16.05" | 15.93" | -3.3 mm |
| Approved rim width | 5.5–7.5" | 6–8" | overlap 6–7.5" |
Both are approved on a rim 6" to 7.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 205/75R20. Fit 215/70R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.6 mph | -0.4 |
| 70 mph | 69.4 mph | -0.6 |
| 90 mph | 89.3 mph | -0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,920 on the road, so it over-counts by 80. At a true 70 mph the first turns 733 times a minute, the second 739.