155/55R15 vs 165/50R15
Going from one to the other changes the overall height by -1.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/55R15 | 165/50R15 | Change |
|---|---|---|---|
| Overall height | 21.7" | 21.5" | -1.0 % |
| Sidewall | 3.36" | 3.25" | -3.2 % |
| Section width | 155 mm | 165 mm | +6.5 % |
| Circumference | 68.2" | 67.5" | -1.0 % |
| Revs per mile | 929 | 938 | +1.0 % |
| Axle height | 10.86" | 10.75" | -2.8 mm |
| Approved rim width | 4–5.5" | 4.5–6" | overlap 4.5–5.5" |
Both are approved on a rim 4.5" to 5.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 155/55R15. Fit 165/50R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.5 mph | -0.5 |
| 70 mph | 69.3 mph | -0.7 |
| 90 mph | 89.1 mph | -0.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,900 on the road, so it over-counts by 100. At a true 70 mph the first turns 1084 times a minute, the second 1095.