185/70R14 vs 175/70R14
Going from one to the other changes the overall height by -2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/70R14 | 175/70R14 | Change |
|---|---|---|---|
| Overall height | 24.2" | 23.6" | -2.3 % |
| Sidewall | 5.10" | 4.82" | -5.4 % |
| Section width | 185 mm | 175 mm | -5.4 % |
| Circumference | 76.0" | 74.3" | -2.3 % |
| Revs per mile | 834 | 853 | +2.3 % |
| Axle height | 12.10" | 11.82" | -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 185/70R14. Fit 175/70R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 87.9 mph | -2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,772 on the road, so it over-counts by 228. At a true 70 mph the first turns 972 times a minute, the second 995.