265/75R19.5 vs 265/80R19.5
Going from one to the other changes the overall height by +3.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/75R19.5 | 265/80R19.5 | Change |
|---|---|---|---|
| Overall height | 35.1" | 36.2" | +3.0 % |
| Sidewall | 7.82" | 8.35" | +6.7 % |
| Section width | 265 mm | 265 mm | 0.0 % |
| Circumference | 110.4" | 113.7" | +3.0 % |
| Revs per mile | 574 | 557 | -3.0 % |
| Axle height | 17.57" | 18.10" | +13.3 mm |
| Approved rim width | 7.5–9.5" | 7.5–9.5" | overlap 7.5–9.5" |
Both are approved on a rim 7.5" to 9.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 265/75R19.5. Fit 265/80R19.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.5 mph | +1.5 |
| 70 mph | 72.1 mph | +2.1 |
| 90 mph | 92.7 mph | +2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,297 on the road, so it under-counts by 297. At a true 70 mph the first turns 669 times a minute, the second 650.