275/75R22.5 vs 265/80R22.5
Going from one to the other changes the overall height by +1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/75R22.5 | 265/80R22.5 | Change |
|---|---|---|---|
| Overall height | 38.7" | 39.2" | +1.2 % |
| Sidewall | 8.12" | 8.35" | +2.8 % |
| Section width | 275 mm | 265 mm | -3.6 % |
| Circumference | 121.7" | 123.1" | +1.2 % |
| Revs per mile | 521 | 515 | -1.2 % |
| Axle height | 19.37" | 19.60" | +5.8 mm |
| Approved rim width | 7.5–10" | 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 275/75R22.5. Fit 265/80R22.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.8 mph | +0.8 |
| 90 mph | 91.1 mph | +1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,117 on the road, so it under-counts by 117. At a true 70 mph the first turns 607 times a minute, the second 600.