215/55R18 vs 205/60R18
Going from one to the other changes the overall height by +1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/55R18 | 205/60R18 | Change |
|---|---|---|---|
| Overall height | 27.3" | 27.7" | +1.4 % |
| Sidewall | 4.66" | 4.84" | +4.0 % |
| Section width | 215 mm | 205 mm | -4.7 % |
| Circumference | 85.8" | 87.0" | +1.4 % |
| Revs per mile | 738 | 728 | -1.4 % |
| Axle height | 13.66" | 13.84" | +4.8 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 215/55R18. Fit 205/60R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,137 on the road, so it under-counts by 137. At a true 70 mph the first turns 862 times a minute, the second 850.
What drivers reported
215/55R18 carries 10 complaints. Nobody has filed one naming 205/60R18.