215/40R18 vs 195/40R18
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/40R18 | 195/40R18 | Change |
|---|---|---|---|
| Overall height | 24.8" | 24.1" | -2.5 % |
| Sidewall | 3.39" | 3.07" | -9.3 % |
| Section width | 215 mm | 195 mm | -9.3 % |
| Circumference | 77.8" | 75.8" | -2.5 % |
| Revs per mile | 814 | 835 | +2.5 % |
| Axle height | 12.39" | 12.07" | -8.0 mm |
| Approved rim width | 6–8" | 5.5–7" | overlap 6–7" |
Both are approved on a rim 6" to 7" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 215/40R18. Fit 195/40R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.7 mph | -1.3 |
| 70 mph | 68.2 mph | -1.8 |
| 90 mph | 87.7 mph | -2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,746 on the road, so it over-counts by 254. At a true 70 mph the first turns 950 times a minute, the second 975.
What drivers reported
215/40R18 carries 2 complaints. Nobody has filed one naming 195/40R18.