185/50R15 vs 165/55R15
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 | 185/50R15 | 165/55R15 | Change |
|---|---|---|---|
| Overall height | 22.3" | 22.1" | -0.6 % |
| Sidewall | 3.64" | 3.57" | -1.9 % |
| Section width | 185 mm | 165 mm | -10.8 % |
| Circumference | 70.0" | 69.6" | -0.6 % |
| Revs per mile | 905 | 911 | +0.6 % |
| Axle height | 11.14" | 11.07" | -1.8 mm |
| Approved rim width | 5–6.5" | 4.5–6" | 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 165/55R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.7 mph | -0.3 |
| 70 mph | 69.6 mph | -0.4 |
| 90 mph | 89.4 mph | -0.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,938 on the road, so it over-counts by 62. At a true 70 mph the first turns 1056 times a minute, the second 1062.
What drivers reported
185/50R15 carries 2 complaints. Nobody has filed one naming 165/55R15.