145/55R14 vs 125/65R14
Going from one to the other changes the overall height by +0.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 145/55R14 | 125/65R14 | Change |
|---|---|---|---|
| Overall height | 20.3" | 20.4" | +0.6 % |
| Sidewall | 3.14" | 3.20" | +1.9 % |
| Section width | 145 mm | 125 mm | -13.8 % |
| Circumference | 63.7" | 64.1" | +0.6 % |
| Revs per mile | 995 | 989 | -0.6 % |
| Axle height | 10.14" | 10.20" | +1.5 mm |
| Approved rim width | 4–5.5" | 3.5–4.5" | overlap 4–4.5" |
Both are approved on a rim 4" to 4.5" 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 125/65R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.3 mph | +0.3 |
| 70 mph | 70.4 mph | +0.4 |
| 90 mph | 90.5 mph | +0.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,058 on the road, so it under-counts by 58. At a true 70 mph the first turns 1160 times a minute, the second 1154.