195/60R18 vs 195/55R18
Going from one to the other changes the overall height by -2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 195/60R18 | 195/55R18 | Change |
|---|---|---|---|
| Overall height | 27.2" | 26.4" | -2.8 % |
| Sidewall | 4.61" | 4.22" | -8.3 % |
| Section width | 195 mm | 195 mm | 0.0 % |
| Circumference | 85.5" | 83.1" | -2.8 % |
| Revs per mile | 741 | 763 | +2.8 % |
| Axle height | 13.61" | 13.22" | -9.8 mm |
| Approved rim width | 5.5–7" | 5.5–7" | overlap 5.5–7" |
Both are approved on a rim 5.5" to 7" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 195/60R18. Fit 195/55R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,718 on the road, so it over-counts by 282. At a true 70 mph the first turns 865 times a minute, the second 890.