215/80R16 vs 205/85R16
Going from one to the other changes the overall height by +0.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/80R16 | 205/85R16 | Change |
|---|---|---|---|
| Overall height | 29.5" | 29.7" | +0.6 % |
| Sidewall | 6.77" | 6.86" | +1.3 % |
| Section width | 215 mm | 205 mm | -4.7 % |
| Circumference | 92.8" | 93.4" | +0.6 % |
| Revs per mile | 683 | 679 | -0.6 % |
| Axle height | 14.77" | 14.86" | +2.3 mm |
| Approved rim width | 6–8" | 5.5–7.5" | 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 215/80R16. Fit 205/85R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.3 mph | +0.3 |
| 70 mph | 70.4 mph | +0.4 |
| 90 mph | 90.5 mph | +0.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,060 on the road, so it under-counts by 60. At a true 70 mph the first turns 796 times a minute, the second 792.