175/55R15 vs 185/50R15
Going from one to the other changes the overall height by -1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/55R15 | 185/50R15 | Change |
|---|---|---|---|
| Overall height | 22.6" | 22.3" | -1.3 % |
| Sidewall | 3.79" | 3.64" | -3.9 % |
| Section width | 175 mm | 185 mm | +5.7 % |
| Circumference | 70.9" | 70.0" | -1.3 % |
| Revs per mile | 893 | 905 | +1.3 % |
| Axle height | 11.29" | 11.14" | -3.8 mm |
| Approved rim width | 5–6" | 5–6.5" | overlap 5–6" |
Both are approved on a rim 5" to 6" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 175/55R15. Fit 185/50R15 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 | 69.1 mph | -0.9 |
| 90 mph | 88.8 mph | -1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,869 on the road, so it over-counts by 131. At a true 70 mph the first turns 1042 times a minute, the second 1056.
What drivers reported
Nobody has filed a complaint naming 175/55R15. 185/50R15 carries 2.