155/75R17 vs 175/70R17
Going from one to the other changes the overall height by +1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/75R17 | 175/70R17 | Change |
|---|---|---|---|
| Overall height | 26.2" | 26.6" | +1.9 % |
| Sidewall | 4.58" | 4.82" | +5.4 % |
| Section width | 155 mm | 175 mm | +12.9 % |
| Circumference | 82.2" | 83.7" | +1.9 % |
| Revs per mile | 771 | 757 | -1.9 % |
| Axle height | 13.08" | 13.32" | +6.3 mm |
| Approved rim width | 4–5.5" | 5–6" | 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 155/75R17. Fit 175/70R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,188 on the road, so it under-counts by 188. At a true 70 mph the first turns 900 times a minute, the second 883.