145/55R14 vs 165/50R14
Going from one to the other changes the overall height by +1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 145/55R14 | 165/50R14 | Change |
|---|---|---|---|
| Overall height | 20.3" | 20.5" | +1.1 % |
| Sidewall | 3.14" | 3.25" | +3.4 % |
| Section width | 145 mm | 165 mm | +13.8 % |
| Circumference | 63.7" | 64.4" | +1.1 % |
| Revs per mile | 995 | 984 | -1.1 % |
| Axle height | 10.14" | 10.25" | +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 145/55R14. Fit 165/50R14 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 | 91.0 mph | +1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,107 on the road, so it under-counts by 107. At a true 70 mph the first turns 1160 times a minute, the second 1148.