305/35R22 vs 325/35R22
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 | 305/35R22 | 325/35R22 | Change |
|---|---|---|---|
| Overall height | 30.4" | 31.0" | +1.8 % |
| Sidewall | 4.20" | 4.48" | +6.6 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 95.5" | 97.3" | +1.8 % |
| Revs per mile | 663 | 651 | -1.8 % |
| Axle height | 15.20" | 15.48" | +7.0 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 305/35R22. Fit 325/35R22 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 | 71.3 mph | +1.3 |
| 90 mph | 91.6 mph | +1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,181 on the road, so it under-counts by 181. At a true 70 mph the first turns 774 times a minute, the second 760.