325/40R22 vs 305/40R22
Going from one to the other changes the overall height by -2.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/40R22 | 305/40R22 | Change |
|---|---|---|---|
| Overall height | 32.2" | 31.6" | -2.0 % |
| Sidewall | 5.12" | 4.80" | -6.2 % |
| Section width | 325 mm | 305 mm | -6.2 % |
| Circumference | 101.3" | 99.3" | -2.0 % |
| Revs per mile | 626 | 638 | +2.0 % |
| Axle height | 16.12" | 15.80" | -8.0 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 305/40R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.0 mph | -1.0 |
| 70 mph | 68.6 mph | -1.4 |
| 90 mph | 88.2 mph | -1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,805 on the road, so it over-counts by 195. At a true 70 mph the first turns 730 times a minute, the second 744.
What drivers reported
Nobody has filed a complaint naming 325/40R22. 305/40R22 carries 7.