185/70R16 vs 175/70R16
Going from one to the other changes the overall height by -2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/70R16 | 175/70R16 | Change |
|---|---|---|---|
| Overall height | 26.2" | 25.6" | -2.1 % |
| Sidewall | 5.10" | 4.82" | -5.4 % |
| Section width | 185 mm | 175 mm | -5.4 % |
| Circumference | 82.3" | 80.6" | -2.1 % |
| Revs per mile | 770 | 786 | +2.1 % |
| Axle height | 13.10" | 12.82" | -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 185/70R16. Fit 175/70R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.5 mph | -1.5 |
| 90 mph | 88.1 mph | -1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,790 on the road, so it over-counts by 210. At a true 70 mph the first turns 898 times a minute, the second 917.