195/60R18 vs 185/65R18
Going from one to the other changes the overall height by +0.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 195/60R18 | 185/65R18 | Change |
|---|---|---|---|
| Overall height | 27.2" | 27.5" | +0.9 % |
| Sidewall | 4.61" | 4.73" | +2.8 % |
| Section width | 195 mm | 185 mm | -5.1 % |
| Circumference | 85.5" | 86.3" | +0.9 % |
| Revs per mile | 741 | 734 | -0.9 % |
| Axle height | 13.61" | 13.73" | +3.3 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 195/60R18. Fit 185/65R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.5 mph | +0.5 |
| 70 mph | 70.7 mph | +0.7 |
| 90 mph | 90.8 mph | +0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,094 on the road, so it under-counts by 94. At a true 70 mph the first turns 865 times a minute, the second 857.