185/70R17 vs 175/70R17
Going from one to the other changes the overall height by -2.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/70R17 | 175/70R17 | Change |
|---|---|---|---|
| Overall height | 27.2" | 26.6" | -2.0 % |
| Sidewall | 5.10" | 4.82" | -5.4 % |
| Section width | 185 mm | 175 mm | -5.4 % |
| Circumference | 85.4" | 83.7" | -2.0 % |
| Revs per mile | 742 | 757 | +2.0 % |
| Axle height | 13.60" | 13.32" | -7.0 mm |
| Approved rim width | 5–6.5" | 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 185/70R17. Fit 175/70R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.0 mph | -1.0 |
| 70 mph | 68.6 mph | -1.4 |
| 90 mph | 88.2 mph | -1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,797 on the road, so it over-counts by 203. At a true 70 mph the first turns 865 times a minute, the second 883.