185/85R18 vs 195/85R18
Going from one to the other changes the overall height by +2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/85R18 | 195/85R18 | Change |
|---|---|---|---|
| Overall height | 30.4" | 31.1" | +2.2 % |
| Sidewall | 6.19" | 6.53" | +5.4 % |
| Section width | 185 mm | 195 mm | +5.4 % |
| Circumference | 95.4" | 97.6" | +2.2 % |
| Revs per mile | 664 | 650 | -2.2 % |
| Axle height | 15.19" | 15.53" | +8.5 mm |
| Approved rim width | 5–6.5" | 5.5–7" | 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 185/85R18. Fit 195/85R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.5 mph | +1.5 |
| 90 mph | 92.0 mph | +2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,220 on the road, so it under-counts by 220. At a true 70 mph the first turns 774 times a minute, the second 758.