205/85R20 vs 215/80R20
Going from one to the other changes the overall height by -0.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/85R20 | 215/80R20 | Change |
|---|---|---|---|
| Overall height | 33.7" | 33.5" | -0.5 % |
| Sidewall | 6.86" | 6.77" | -1.3 % |
| Section width | 205 mm | 215 mm | +4.9 % |
| Circumference | 105.9" | 105.4" | -0.5 % |
| Revs per mile | 598 | 601 | +0.5 % |
| Axle height | 16.86" | 16.77" | -2.3 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 205/85R20. Fit 215/80R20 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 | 69.6 mph | -0.4 |
| 90 mph | 89.5 mph | -0.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,947 on the road, so it over-counts by 53. At a true 70 mph the first turns 698 times a minute, the second 701.