165/60R15 vs 145/70R15
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 | 165/60R15 | 145/70R15 | Change |
|---|---|---|---|
| Overall height | 22.8" | 23.0" | +0.9 % |
| Sidewall | 3.90" | 4.00" | +2.5 % |
| Section width | 165 mm | 145 mm | -12.1 % |
| Circumference | 71.6" | 72.2" | +0.9 % |
| Revs per mile | 885 | 877 | -0.9 % |
| Axle height | 11.40" | 11.50" | +2.5 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 165/60R15. Fit 145/70R15 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 10,086 on the road, so it under-counts by 86. At a true 70 mph the first turns 1032 times a minute, the second 1023.