155/50R15 vs 165/50R15
Going from one to the other changes the overall height by +1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/50R15 | 165/50R15 | Change |
|---|---|---|---|
| Overall height | 21.1" | 21.5" | +1.9 % |
| Sidewall | 3.05" | 3.25" | +6.5 % |
| Section width | 155 mm | 165 mm | +6.5 % |
| Circumference | 66.3" | 67.5" | +1.9 % |
| Revs per mile | 956 | 938 | -1.9 % |
| Axle height | 10.55" | 10.75" | +5.0 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 155/50R15. Fit 165/50R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,187 on the road, so it under-counts by 187. At a true 70 mph the first turns 1115 times a minute, the second 1095.