275/45R16 vs 285/40R16
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 | 275/45R16 | 285/40R16 | Change |
|---|---|---|---|
| Overall height | 25.7" | 25.0" | -3.0 % |
| Sidewall | 4.87" | 4.49" | -7.9 % |
| Section width | 275 mm | 285 mm | +3.6 % |
| Circumference | 80.9" | 78.5" | -3.0 % |
| Revs per mile | 783 | 807 | +3.0 % |
| Axle height | 12.87" | 12.49" | -9.8 mm |
| Approved rim width | 7.5–10" | 8–10.5" | overlap 8–10" |
Both are approved on a rim 8" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 275/45R16. Fit 285/40R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.5 mph | -1.5 |
| 70 mph | 67.9 mph | -2.1 |
| 90 mph | 87.3 mph | -2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,702 on the road, so it over-counts by 298. At a true 70 mph the first turns 914 times a minute, the second 942.