155/70R13 vs 145/75R13
Going from one to the other changes the overall height by +0.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/70R13 | 145/75R13 | Change |
|---|---|---|---|
| Overall height | 21.5" | 21.6" | +0.1 % |
| Sidewall | 4.27" | 4.28" | +0.2 % |
| Section width | 155 mm | 145 mm | -6.5 % |
| Circumference | 67.7" | 67.7" | +0.1 % |
| Revs per mile | 936 | 935 | -0.1 % |
| Axle height | 10.77" | 10.78" | +0.3 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 155/70R13. Fit 145/75R13 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.0 mph | +0.0 |
| 50 mph | 50.0 mph | +0.0 |
| 70 mph | 70.1 mph | +0.1 |
| 90 mph | 90.1 mph | +0.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,009 on the road, so it under-counts by 9. At a true 70 mph the first turns 1092 times a minute, the second 1091.