305/45R22 vs 325/40R22
Going from one to the other changes the overall height by -1.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/45R22 | 325/40R22 | Change |
|---|---|---|---|
| Overall height | 32.8" | 32.2" | -1.7 % |
| Sidewall | 5.40" | 5.12" | -5.3 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 103.1" | 101.3" | -1.7 % |
| Revs per mile | 615 | 626 | +1.7 % |
| Axle height | 16.40" | 16.12" | -7.3 mm |
| Approved rim width | 8.5–11" | 9–12" | overlap 9–11" |
Both are approved on a rim 9" to 11" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 305/45R22. Fit 325/40R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.4 mph | -1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,826 on the road, so it over-counts by 174. At a true 70 mph the first turns 717 times a minute, the second 730.
What drivers reported
305/45R22 carries 2 complaints. Nobody has filed one naming 325/40R22.