305/65R23 vs 325/60R23
Going from one to the other changes the overall height by -0.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/65R23 | 325/60R23 | Change |
|---|---|---|---|
| Overall height | 38.6" | 38.4" | -0.7 % |
| Sidewall | 7.81" | 7.68" | -1.6 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 121.3" | 120.5" | -0.7 % |
| Revs per mile | 522 | 526 | +0.7 % |
| Axle height | 19.31" | 19.18" | -3.3 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 305/65R23. Fit 325/60R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.7 mph | -0.3 |
| 70 mph | 69.5 mph | -0.5 |
| 90 mph | 89.4 mph | -0.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,934 on the road, so it over-counts by 66. At a true 70 mph the first turns 609 times a minute, the second 613.