195/55R18 vs 205/50R18
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 | 195/55R18 | 205/50R18 | Change |
|---|---|---|---|
| Overall height | 26.4" | 26.1" | -1.4 % |
| Sidewall | 4.22" | 4.04" | -4.4 % |
| Section width | 195 mm | 205 mm | +5.1 % |
| Circumference | 83.1" | 81.9" | -1.4 % |
| Revs per mile | 763 | 774 | +1.4 % |
| Axle height | 13.22" | 13.04" | -4.8 mm |
| Approved rim width | 5.5–7" | 5.5–7.5" | 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 195/55R18. Fit 205/50R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.0 mph | -1.0 |
| 90 mph | 88.7 mph | -1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,859 on the road, so it over-counts by 141. At a true 70 mph the first turns 890 times a minute, the second 903.
What drivers reported
Nobody has filed a complaint naming 195/55R18. 205/50R18 carries 2.