285/45R22 vs 305/40R22
Going from one to the other changes the overall height by -1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/45R22 | 305/40R22 | Change |
|---|---|---|---|
| Overall height | 32.1" | 31.6" | -1.5 % |
| Sidewall | 5.05" | 4.80" | -4.9 % |
| Section width | 285 mm | 305 mm | +7.0 % |
| Circumference | 100.8" | 99.3" | -1.5 % |
| Revs per mile | 628 | 638 | +1.5 % |
| Axle height | 16.05" | 15.80" | -6.3 mm |
| Approved rim width | 8–10.5" | 8.5–11" | overlap 8.5–10.5" |
Both are approved on a rim 8.5" to 10.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 285/45R22. Fit 305/40R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.9 mph | -1.1 |
| 90 mph | 88.6 mph | -1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,847 on the road, so it over-counts by 153. At a true 70 mph the first turns 733 times a minute, the second 744.