305/45R23 vs 325/45R23
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 | 305/45R23 | 325/45R23 | Change |
|---|---|---|---|
| Overall height | 33.8" | 34.5" | +2.1 % |
| Sidewall | 5.40" | 5.76" | +6.6 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 106.2" | 108.4" | +2.1 % |
| Revs per mile | 597 | 584 | -2.1 % |
| Axle height | 16.90" | 17.26" | +9.0 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 305/45R23. Fit 325/45R23 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 | 71.5 mph | +1.5 |
| 90 mph | 91.9 mph | +1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,210 on the road, so it under-counts by 210. At a true 70 mph the first turns 696 times a minute, the second 682.