285/40R17 vs 265/45R17
Going from one to the other changes the overall height by +1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/40R17 | 265/45R17 | Change |
|---|---|---|---|
| Overall height | 26.0" | 26.4" | +1.6 % |
| Sidewall | 4.49" | 4.69" | +4.6 % |
| Section width | 285 mm | 265 mm | -7.0 % |
| Circumference | 81.6" | 82.9" | +1.6 % |
| Revs per mile | 776 | 764 | -1.6 % |
| Axle height | 12.99" | 13.19" | +5.3 mm |
| Approved rim width | 8–10.5" | 7.5–9.5" | overlap 8–9.5" |
Both are approved on a rim 8" 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 285/40R17. Fit 265/45R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.1 mph | +1.1 |
| 90 mph | 91.4 mph | +1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,159 on the road, so it under-counts by 159. At a true 70 mph the first turns 906 times a minute, the second 892.