195/85R18 vs 215/80R18
Going from one to the other changes the overall height by +1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 195/85R18 | 215/80R18 | Change |
|---|---|---|---|
| Overall height | 31.1" | 31.5" | +1.6 % |
| Sidewall | 6.53" | 6.77" | +3.8 % |
| Section width | 195 mm | 215 mm | +10.3 % |
| Circumference | 97.6" | 99.1" | +1.6 % |
| Revs per mile | 650 | 639 | -1.6 % |
| Axle height | 15.53" | 15.77" | +6.3 mm |
| Approved rim width | 5.5–7" | 6–8" | overlap 6–7" |
Both are approved on a rim 6" to 7" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 195/85R18. Fit 215/80R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.1 mph | +1.1 |
| 90 mph | 91.4 mph | +1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,158 on the road, so it under-counts by 158. At a true 70 mph the first turns 758 times a minute, the second 746.