215/65R18 vs 195/75R18
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/65R18 | 195/75R18 | Change |
|---|---|---|---|
| Overall height | 29.0" | 29.5" | +1.8 % |
| Sidewall | 5.50" | 5.76" | +4.7 % |
| Section width | 215 mm | 195 mm | -9.3 % |
| Circumference | 91.1" | 92.7" | +1.8 % |
| Revs per mile | 695 | 683 | -1.8 % |
| Axle height | 14.50" | 14.76" | +6.5 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 215/65R18. Fit 195/75R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.2 mph | +1.2 |
| 90 mph | 91.6 mph | +1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,176 on the road, so it under-counts by 176. At a true 70 mph the first turns 811 times a minute, the second 797.