205/65R18 vs 215/65R18
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/65R18 | 215/65R18 | Change |
|---|---|---|---|
| Overall height | 28.5" | 29.0" | +1.8 % |
| Sidewall | 5.25" | 5.50" | +4.9 % |
| Section width | 205 mm | 215 mm | +4.9 % |
| Circumference | 89.5" | 91.1" | +1.8 % |
| Revs per mile | 708 | 695 | -1.8 % |
| Axle height | 14.25" | 14.50" | +6.5 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 205/65R18. Fit 215/65R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.6 mph | +1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,180 on the road, so it under-counts by 180. At a true 70 mph the first turns 826 times a minute, the second 811.