145/65R18 vs 155/65R18
Going from one to the other changes the overall height by +2.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 145/65R18 | 155/65R18 | Change |
|---|---|---|---|
| Overall height | 25.4" | 25.9" | +2.0 % |
| Sidewall | 3.71" | 3.97" | +6.9 % |
| Section width | 145 mm | 155 mm | +6.9 % |
| Circumference | 79.9" | 81.5" | +2.0 % |
| Revs per mile | 793 | 778 | -2.0 % |
| Axle height | 12.71" | 12.97" | +6.5 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 145/65R18. Fit 155/65R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.8 mph | +1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,201 on the road, so it under-counts by 201. At a true 70 mph the first turns 926 times a minute, the second 907.