135/80R15 vs 155/75R15
Going from one to the other changes the overall height by +2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 135/80R15 | 155/75R15 | Change |
|---|---|---|---|
| Overall height | 23.5" | 24.2" | +2.8 % |
| Sidewall | 4.25" | 4.58" | +7.6 % |
| Section width | 135 mm | 155 mm | +14.8 % |
| Circumference | 73.8" | 75.9" | +2.8 % |
| Revs per mile | 858 | 835 | -2.8 % |
| Axle height | 11.75" | 12.08" | +8.3 mm |
| Approved rim width | 3.5–5" | 4–5.5" | overlap 4–5" |
Both are approved on a rim 4" to 5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 135/80R15. 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 | 51.4 mph | +1.4 |
| 70 mph | 71.9 mph | +1.9 |
| 90 mph | 92.5 mph | +2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,276 on the road, so it under-counts by 276. At a true 70 mph the first turns 1001 times a minute, the second 974.