155/60R15 vs 145/65R15
Going from one to the other changes the overall height by +0.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/60R15 | 145/65R15 | Change |
|---|---|---|---|
| Overall height | 22.3" | 22.4" | +0.4 % |
| Sidewall | 3.66" | 3.71" | +1.3 % |
| Section width | 155 mm | 145 mm | -6.5 % |
| Circumference | 70.1" | 70.4" | +0.4 % |
| Revs per mile | 903 | 900 | -0.4 % |
| Axle height | 11.16" | 11.21" | +1.3 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 155/60R15. Fit 145/65R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.2 mph | +0.2 |
| 70 mph | 70.3 mph | +0.3 |
| 90 mph | 90.4 mph | +0.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,044 on the road, so it under-counts by 44. At a true 70 mph the first turns 1054 times a minute, the second 1049.