195/50R15 vs 185/55R15
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 | 195/50R15 | 185/55R15 | Change |
|---|---|---|---|
| Overall height | 22.7" | 23.0" | +1.5 % |
| Sidewall | 3.84" | 4.01" | +4.4 % |
| Section width | 195 mm | 185 mm | -5.1 % |
| Circumference | 71.2" | 72.3" | +1.5 % |
| Revs per mile | 889 | 876 | -1.5 % |
| Axle height | 11.34" | 11.51" | +4.3 mm |
| Approved rim width | 5.5–7" | 5–6.5" | 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 195/50R15. Fit 185/55R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.3 mph | +1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,148 on the road, so it under-counts by 148. At a true 70 mph the first turns 1038 times a minute, the second 1022.