325/40R22 vs 305/45R22
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/40R22 | 305/45R22 | Change |
|---|---|---|---|
| Overall height | 32.2" | 32.8" | +1.8 % |
| Sidewall | 5.12" | 5.40" | +5.6 % |
| Section width | 325 mm | 305 mm | -6.2 % |
| Circumference | 101.3" | 103.1" | +1.8 % |
| Revs per mile | 626 | 615 | -1.8 % |
| Axle height | 16.12" | 16.40" | +7.3 mm |
| Approved rim width | 9–12" | 8.5–11" | 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 325/40R22. Fit 305/45R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.2 mph | +1.2 |
| 90 mph | 91.6 mph | +1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,177 on the road, so it under-counts by 177. At a true 70 mph the first turns 730 times a minute, the second 717.
What drivers reported
Nobody has filed a complaint naming 325/40R22. 305/45R22 carries 2.