215/40R18 vs 195/45R18
Going from one to the other changes the overall height by +0.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/40R18 | 195/45R18 | Change |
|---|---|---|---|
| Overall height | 24.8" | 24.9" | +0.6 % |
| Sidewall | 3.39" | 3.45" | +2.0 % |
| Section width | 215 mm | 195 mm | -9.3 % |
| Circumference | 77.8" | 78.3" | +0.6 % |
| Revs per mile | 814 | 810 | -0.6 % |
| Axle height | 12.39" | 12.45" | +1.8 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 195/45R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.3 mph | +0.3 |
| 70 mph | 70.4 mph | +0.4 |
| 90 mph | 90.5 mph | +0.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,056 on the road, so it under-counts by 56. At a true 70 mph the first turns 950 times a minute, the second 945.
What drivers reported
215/40R18 carries 2 complaints. Nobody has filed one naming 195/45R18.