155/50R14 vs 145/55R14
Going from one to the other changes the overall height by +0.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/50R14 | 145/55R14 | Change |
|---|---|---|---|
| Overall height | 20.1" | 20.3" | +0.9 % |
| Sidewall | 3.05" | 3.14" | +2.9 % |
| Section width | 155 mm | 145 mm | -6.5 % |
| Circumference | 63.2" | 63.7" | +0.9 % |
| Revs per mile | 1003 | 995 | -0.9 % |
| Axle height | 10.05" | 10.14" | +2.2 mm |
| Approved rim width | 4–5.5" | 4–5.5" | overlap 4–5.5" |
Both are approved on a rim 4" 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 155/50R14. Fit 145/55R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.6 mph | +0.6 |
| 90 mph | 90.8 mph | +0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,088 on the road, so it under-counts by 88. At a true 70 mph the first turns 1170 times a minute, the second 1160.