265/45R20 vs 275/40R20
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/45R20 | 275/40R20 | Change |
|---|---|---|---|
| Overall height | 29.4" | 28.7" | -2.5 % |
| Sidewall | 4.69" | 4.33" | -7.8 % |
| Section width | 265 mm | 275 mm | +3.8 % |
| Circumference | 92.3" | 90.0" | -2.5 % |
| Revs per mile | 686 | 704 | +2.5 % |
| Axle height | 14.69" | 14.33" | -9.3 mm |
| Approved rim width | 7.5–9.5" | 7.5–10" | 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 265/45R20. Fit 275/40R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.3 mph | -1.7 |
| 90 mph | 87.8 mph | -2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,752 on the road, so it over-counts by 248. At a true 70 mph the first turns 801 times a minute, the second 821.
What drivers reported
Nobody has filed a complaint naming 265/45R20. 275/40R20 carries 14.