205/80R20 vs 215/75R20
Going from one to the other changes the overall height by -0.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/80R20 | 215/75R20 | Change |
|---|---|---|---|
| Overall height | 32.9" | 32.7" | -0.7 % |
| Sidewall | 6.46" | 6.35" | -1.7 % |
| Section width | 205 mm | 215 mm | +4.9 % |
| Circumference | 103.4" | 102.7" | -0.7 % |
| Revs per mile | 613 | 617 | +0.7 % |
| Axle height | 16.46" | 16.35" | -2.8 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 205/80R20. Fit 215/75R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.7 mph | -0.3 |
| 70 mph | 69.5 mph | -0.5 |
| 90 mph | 89.4 mph | -0.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,934 on the road, so it over-counts by 66. At a true 70 mph the first turns 715 times a minute, the second 720.