195/70R17 vs 185/70R17
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 | 195/70R17 | 185/70R17 | Change |
|---|---|---|---|
| Overall height | 27.7" | 27.2" | -2.0 % |
| Sidewall | 5.37" | 5.10" | -5.1 % |
| Section width | 195 mm | 185 mm | -5.1 % |
| Circumference | 87.2" | 85.4" | -2.0 % |
| Revs per mile | 727 | 742 | +2.0 % |
| Axle height | 13.87" | 13.60" | -7.0 mm |
| Approved rim width | 5.5–7" | 5–6.5" | overlap 5.5–6.5" |
Both are approved on a rim 5.5" to 6.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 195/70R17. Fit 185/70R17 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 9,801 on the road, so it over-counts by 199. At a true 70 mph the first turns 848 times a minute, the second 865.