165/50R15 vs 155/55R15
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 | 165/50R15 | 155/55R15 | Change |
|---|---|---|---|
| Overall height | 21.5" | 21.7" | +1.0 % |
| Sidewall | 3.25" | 3.36" | +3.3 % |
| Section width | 165 mm | 155 mm | -6.1 % |
| Circumference | 67.5" | 68.2" | +1.0 % |
| Revs per mile | 938 | 929 | -1.0 % |
| Axle height | 10.75" | 10.86" | +2.8 mm |
| Approved rim width | 4.5–6" | 4–5.5" | 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 165/50R15. Fit 155/55R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.5 mph | +0.5 |
| 70 mph | 70.7 mph | +0.7 |
| 90 mph | 90.9 mph | +0.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,101 on the road, so it under-counts by 101. At a true 70 mph the first turns 1095 times a minute, the second 1084.