325/30R22 vs 345/25R22
Going from one to the other changes the overall height by -3.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/30R22 | 345/25R22 | Change |
|---|---|---|---|
| Overall height | 29.7" | 28.8" | -3.0 % |
| Sidewall | 3.84" | 3.40" | -11.5 % |
| Section width | 325 mm | 345 mm | +6.2 % |
| Circumference | 93.2" | 90.5" | -3.0 % |
| Revs per mile | 680 | 700 | +3.0 % |
| Axle height | 14.84" | 14.40" | -11.3 mm |
| Approved rim width | 9–12" | 9.5–12.5" | overlap 9.5–12" |
Both are approved on a rim 9.5" to 12" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 325/30R22. Fit 345/25R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.5 mph | -1.5 |
| 70 mph | 67.9 mph | -2.1 |
| 90 mph | 87.3 mph | -2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,702 on the road, so it over-counts by 298. At a true 70 mph the first turns 793 times a minute, the second 817.