185/55R15 vs 195/50R15
Going from one to the other changes the overall height by -1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/55R15 | 195/50R15 | Change |
|---|---|---|---|
| Overall height | 23.0" | 22.7" | -1.5 % |
| Sidewall | 4.01" | 3.84" | -4.2 % |
| Section width | 185 mm | 195 mm | +5.4 % |
| Circumference | 72.3" | 71.2" | -1.5 % |
| Revs per mile | 876 | 889 | +1.5 % |
| Axle height | 11.51" | 11.34" | -4.3 mm |
| Approved rim width | 5–6.5" | 5.5–7" | overlap 5.5–6.5" |
Both are approved on a rim 5.5" to 6.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 185/55R15. Fit 195/50R15 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 9,855 on the road, so it over-counts by 145. At a true 70 mph the first turns 1022 times a minute, the second 1038.