305/50R23 vs 325/45R23
Going from one to the other changes the overall height by -1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/50R23 | 325/45R23 | Change |
|---|---|---|---|
| Overall height | 35.0" | 34.5" | -1.4 % |
| Sidewall | 6.00" | 5.76" | -4.1 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 110.0" | 108.4" | -1.4 % |
| Revs per mile | 576 | 584 | +1.4 % |
| Axle height | 17.50" | 17.26" | -6.3 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 305/50R23. Fit 325/45R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.0 mph | -1.0 |
| 90 mph | 88.7 mph | -1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,859 on the road, so it over-counts by 141. At a true 70 mph the first turns 672 times a minute, the second 682.