245/45R20 vs 265/40R20
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 | 245/45R20 | 265/40R20 | Change |
|---|---|---|---|
| Overall height | 28.7" | 28.3" | -1.2 % |
| Sidewall | 4.34" | 4.17" | -3.9 % |
| Section width | 245 mm | 265 mm | +8.2 % |
| Circumference | 90.1" | 89.1" | -1.2 % |
| Revs per mile | 703 | 711 | +1.2 % |
| Axle height | 14.34" | 14.17" | -4.3 mm |
| Approved rim width | 7–9" | 7.5–9.5" | overlap 7.5–9" |
Both are approved on a rim 7.5" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 245/45R20. Fit 265/40R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.2 mph | -0.8 |
| 90 mph | 88.9 mph | -1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,883 on the road, so it over-counts by 117. At a true 70 mph the first turns 820 times a minute, the second 830.
What drivers reported
245/45R20 carries 9 complaints. Nobody has filed one naming 265/40R20.