325/65R23 vs 345/60R23
Going from one to the other changes the overall height by -0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/65R23 | 345/60R23 | Change |
|---|---|---|---|
| Overall height | 39.6" | 39.3" | -0.8 % |
| Sidewall | 8.32" | 8.15" | -2.0 % |
| Section width | 325 mm | 345 mm | +6.2 % |
| Circumference | 124.5" | 123.5" | -0.8 % |
| Revs per mile | 509 | 513 | +0.8 % |
| Axle height | 19.82" | 19.65" | -4.3 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 325/65R23. Fit 345/60R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.6 mph | -0.4 |
| 70 mph | 69.4 mph | -0.6 |
| 90 mph | 89.2 mph | -0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,916 on the road, so it over-counts by 84. At a true 70 mph the first turns 594 times a minute, the second 599.