165/70R14 vs 145/75R14
Going from one to the other changes the overall height by -2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 165/70R14 | 145/75R14 | Change |
|---|---|---|---|
| Overall height | 23.1" | 22.6" | -2.3 % |
| Sidewall | 4.55" | 4.28" | -5.8 % |
| Section width | 165 mm | 145 mm | -12.1 % |
| Circumference | 72.6" | 70.9" | -2.3 % |
| Revs per mile | 873 | 894 | +2.3 % |
| Axle height | 11.55" | 11.28" | -6.8 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 165/70R14. Fit 145/75R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 87.9 mph | -2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,770 on the road, so it over-counts by 230. At a true 70 mph the first turns 1019 times a minute, the second 1043.