185/50R15 vs 175/55R15
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 | 185/50R15 | 175/55R15 | Change |
|---|---|---|---|
| Overall height | 22.3" | 22.6" | +1.3 % |
| Sidewall | 3.64" | 3.79" | +4.1 % |
| Section width | 185 mm | 175 mm | -5.4 % |
| Circumference | 70.0" | 70.9" | +1.3 % |
| Revs per mile | 905 | 893 | -1.3 % |
| Axle height | 11.14" | 11.29" | +3.8 mm |
| Approved rim width | 5–6.5" | 5–6" | 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 185/50R15. Fit 175/55R15 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 | 70.9 mph | +0.9 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,133 on the road, so it under-counts by 133. At a true 70 mph the first turns 1056 times a minute, the second 1042.
What drivers reported
185/50R15 carries 2 complaints. Nobody has filed one naming 175/55R15.