175/75R17 vs 175/70R17
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/75R17 | 175/70R17 | Change |
|---|---|---|---|
| Overall height | 27.3" | 26.6" | -2.5 % |
| Sidewall | 5.17" | 4.82" | -6.7 % |
| Section width | 175 mm | 175 mm | 0.0 % |
| Circumference | 85.9" | 83.7" | -2.5 % |
| Revs per mile | 738 | 757 | +2.5 % |
| Axle height | 13.67" | 13.32" | -8.8 mm |
| Approved rim width | 5–6" | 5–6" | overlap 5–6" |
Both are approved on a rim 5" to 6" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 175/75R17. Fit 175/70R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.7 mph | -1.3 |
| 70 mph | 68.2 mph | -1.8 |
| 90 mph | 87.7 mph | -2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,748 on the road, so it over-counts by 252. At a true 70 mph the first turns 861 times a minute, the second 883.