195/75R18 vs 195/80R18
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 195/75R18 | 195/80R18 | Change |
|---|---|---|---|
| Overall height | 29.5" | 30.3" | +2.6 % |
| Sidewall | 5.76" | 6.14" | +6.7 % |
| Section width | 195 mm | 195 mm | 0.0 % |
| Circumference | 92.7" | 95.1" | +2.6 % |
| Revs per mile | 683 | 666 | -2.6 % |
| Axle height | 14.76" | 15.14" | +9.8 mm |
| Approved rim width | 5.5–7" | 5.5–7" | overlap 5.5–7" |
Both are approved on a rim 5.5" to 7" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 195/75R18. Fit 195/80R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,260 on the road, so it under-counts by 260. At a true 70 mph the first turns 797 times a minute, the second 777.