325/45R22 vs 305/50R22
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 | 325/45R22 | 305/50R22 | Change |
|---|---|---|---|
| Overall height | 33.5" | 34.0" | +1.5 % |
| Sidewall | 5.76" | 6.00" | +4.3 % |
| Section width | 325 mm | 305 mm | -6.2 % |
| Circumference | 105.3" | 106.8" | +1.5 % |
| Revs per mile | 602 | 593 | -1.5 % |
| Axle height | 16.76" | 17.00" | +6.3 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 325/45R22. Fit 305/50R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.3 mph | +1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,147 on the road, so it under-counts by 147. At a true 70 mph the first turns 702 times a minute, the second 692.