225/55R18 vs 205/60R18
Going from one to the other changes the overall height by -0.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/55R18 | 205/60R18 | Change |
|---|---|---|---|
| Overall height | 27.7" | 27.7" | -0.2 % |
| Sidewall | 4.87" | 4.84" | -0.6 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 87.2" | 87.0" | -0.2 % |
| Revs per mile | 727 | 728 | +0.2 % |
| Axle height | 13.87" | 13.84" | -0.8 mm |
| Approved rim width | 6–8.5" | 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 225/55R18. Fit 205/60R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.9 mph | -0.1 |
| 50 mph | 49.9 mph | -0.1 |
| 70 mph | 69.9 mph | -0.1 |
| 90 mph | 89.8 mph | -0.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,979 on the road, so it over-counts by 21. At a true 70 mph the first turns 848 times a minute, the second 850.
What drivers reported
225/55R18 carries 11 complaints. Nobody has filed one naming 205/60R18.