175/75R15 vs 155/80R15
Going from one to the other changes the overall height by -2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/75R15 | 155/80R15 | Change |
|---|---|---|---|
| Overall height | 25.3" | 24.8" | -2.3 % |
| Sidewall | 5.17" | 4.88" | -5.5 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 79.6" | 77.8" | -2.3 % |
| Revs per mile | 796 | 814 | +2.3 % |
| Axle height | 12.67" | 12.38" | -7.3 mm |
| Approved rim width | 5–6" | 4–5.5" | overlap 5–5.5" |
Both are approved on a rim 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 175/75R15. Fit 155/80R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 88.0 mph | -2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,775 on the road, so it over-counts by 225. At a true 70 mph the first turns 929 times a minute, the second 950.
What drivers reported
Nobody has filed a complaint naming 175/75R15. 155/80R15 carries 1.