215/70R18 vs 195/80R18
Going from one to the other changes the overall height by +1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/70R18 | 195/80R18 | Change |
|---|---|---|---|
| Overall height | 29.9" | 30.3" | +1.5 % |
| Sidewall | 5.93" | 6.14" | +3.7 % |
| Section width | 215 mm | 195 mm | -9.3 % |
| Circumference | 93.8" | 95.1" | +1.5 % |
| Revs per mile | 676 | 666 | -1.5 % |
| Axle height | 14.93" | 15.14" | +5.5 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 215/70R18. Fit 195/80R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.3 mph | +1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,145 on the road, so it under-counts by 145. At a true 70 mph the first turns 788 times a minute, the second 777.