325/30R22 vs 345/30R22
Going from one to the other changes the overall height by +1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/30R22 | 345/30R22 | Change |
|---|---|---|---|
| Overall height | 29.7" | 30.1" | +1.6 % |
| Sidewall | 3.84" | 4.07" | +6.2 % |
| Section width | 325 mm | 345 mm | +6.2 % |
| Circumference | 93.2" | 94.7" | +1.6 % |
| Revs per mile | 680 | 669 | -1.6 % |
| Axle height | 14.84" | 15.07" | +6.0 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 345/30R22 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.1 mph | +1.1 |
| 90 mph | 91.4 mph | +1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,159 on the road, so it under-counts by 159. At a true 70 mph the first turns 793 times a minute, the second 780.