175/70R17 vs 155/80R17
Going from one to the other changes the overall height by +0.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/70R17 | 155/80R17 | Change |
|---|---|---|---|
| Overall height | 26.6" | 26.8" | +0.4 % |
| Sidewall | 4.82" | 4.88" | +1.2 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 83.7" | 84.1" | +0.4 % |
| Revs per mile | 757 | 754 | -0.4 % |
| Axle height | 13.32" | 13.38" | +1.5 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 175/70R17. Fit 155/80R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.2 mph | +0.2 |
| 70 mph | 70.3 mph | +0.3 |
| 90 mph | 90.4 mph | +0.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,044 on the road, so it under-counts by 44. At a true 70 mph the first turns 883 times a minute, the second 879.
What drivers reported
Nobody has filed a complaint naming 175/70R17. 155/80R17 carries 5.