145/75R15 vs 155/75R15
Going from one to the other changes the overall height by +2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 145/75R15 | 155/75R15 | Change |
|---|---|---|---|
| Overall height | 23.6" | 24.2" | +2.5 % |
| Sidewall | 4.28" | 4.58" | +6.9 % |
| Section width | 145 mm | 155 mm | +6.9 % |
| Circumference | 74.0" | 75.9" | +2.5 % |
| Revs per mile | 856 | 835 | -2.5 % |
| Axle height | 11.78" | 12.08" | +7.5 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 145/75R15. Fit 155/75R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,251 on the road, so it under-counts by 251. At a true 70 mph the first turns 999 times a minute, the second 974.