195/50R18 vs 195/55R18
Going from one to the other changes the overall height by +3.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 195/50R18 | 195/55R18 | Change |
|---|---|---|---|
| Overall height | 25.7" | 26.4" | +3.0 % |
| Sidewall | 3.84" | 4.22" | +10.0 % |
| Section width | 195 mm | 195 mm | 0.0 % |
| Circumference | 80.7" | 83.1" | +3.0 % |
| Revs per mile | 785 | 763 | -3.0 % |
| Axle height | 12.84" | 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 195/50R18. Fit 195/55R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.5 mph | +1.5 |
| 70 mph | 72.1 mph | +2.1 |
| 90 mph | 92.7 mph | +2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,299 on the road, so it under-counts by 299. At a true 70 mph the first turns 916 times a minute, the second 890.