165/55R15 vs 185/50R15
Going from one to the other changes the overall height by +0.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 165/55R15 | 185/50R15 | Change |
|---|---|---|---|
| Overall height | 22.1" | 22.3" | +0.6 % |
| Sidewall | 3.57" | 3.64" | +1.9 % |
| Section width | 165 mm | 185 mm | +12.1 % |
| Circumference | 69.6" | 70.0" | +0.6 % |
| Revs per mile | 911 | 905 | -0.6 % |
| Axle height | 11.07" | 11.14" | +1.8 mm |
| Approved rim width | 4.5–6" | 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 165/55R15. Fit 185/50R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.3 mph | +0.3 |
| 70 mph | 70.4 mph | +0.4 |
| 90 mph | 90.6 mph | +0.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,062 on the road, so it under-counts by 62. At a true 70 mph the first turns 1062 times a minute, the second 1056.
What drivers reported
Nobody has filed a complaint naming 165/55R15. 185/50R15 carries 2.