305/65R23 vs 325/65R23
Going from one to the other changes the overall height by +2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/65R23 | 325/65R23 | Change |
|---|---|---|---|
| Overall height | 38.6" | 39.6" | +2.7 % |
| Sidewall | 7.81" | 8.32" | +6.6 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 121.3" | 124.5" | +2.7 % |
| Revs per mile | 522 | 509 | -2.7 % |
| Axle height | 19.31" | 19.82" | +13.0 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 305/65R23. Fit 325/65R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.9 mph | +1.9 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,265 on the road, so it under-counts by 265. At a true 70 mph the first turns 609 times a minute, the second 594.