325/45R23 vs 345/45R23
Going from one to the other changes the overall height by +2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/45R23 | 345/45R23 | Change |
|---|---|---|---|
| Overall height | 34.5" | 35.2" | +2.1 % |
| Sidewall | 5.76" | 6.11" | +6.2 % |
| Section width | 325 mm | 345 mm | +6.2 % |
| Circumference | 108.4" | 110.7" | +2.1 % |
| Revs per mile | 584 | 573 | -2.1 % |
| Axle height | 17.26" | 17.61" | +9.0 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 325/45R23. Fit 345/45R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.8 mph | +1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,205 on the road, so it under-counts by 205. At a true 70 mph the first turns 682 times a minute, the second 668.