205/85R18 vs 215/85R18
Going from one to the other changes the overall height by +2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/85R18 | 215/85R18 | Change |
|---|---|---|---|
| Overall height | 31.7" | 32.4" | +2.1 % |
| Sidewall | 6.86" | 7.19" | +4.9 % |
| Section width | 205 mm | 215 mm | +4.9 % |
| Circumference | 99.7" | 101.8" | +2.1 % |
| Revs per mile | 636 | 623 | -2.1 % |
| Axle height | 15.86" | 16.19" | +8.5 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 205/85R18. Fit 215/85R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.5 mph | +1.5 |
| 90 mph | 91.9 mph | +1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,211 on the road, so it under-counts by 211. At a true 70 mph the first turns 742 times a minute, the second 726.