205/70R18 vs 215/70R18
Going from one to the other changes the overall height by +1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/70R18 | 215/70R18 | Change |
|---|---|---|---|
| Overall height | 29.3" | 29.9" | +1.9 % |
| Sidewall | 5.65" | 5.93" | +4.9 % |
| Section width | 205 mm | 215 mm | +4.9 % |
| Circumference | 92.0" | 93.8" | +1.9 % |
| Revs per mile | 688 | 676 | -1.9 % |
| Axle height | 14.65" | 14.93" | +7.0 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 205/70R18. Fit 215/70R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,188 on the road, so it under-counts by 188. At a true 70 mph the first turns 803 times a minute, the second 788.