345/35R23 vs 325/35R23
Going from one to the other changes the overall height by -1.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/35R23 | 325/35R23 | Change |
|---|---|---|---|
| Overall height | 32.5" | 32.0" | -1.7 % |
| Sidewall | 4.75" | 4.48" | -5.8 % |
| Section width | 345 mm | 325 mm | -5.8 % |
| Circumference | 102.1" | 100.4" | -1.7 % |
| Revs per mile | 620 | 631 | +1.7 % |
| Axle height | 16.25" | 15.98" | -7.0 mm |
| Approved rim width | 9.5–12.5" | 9–12" | 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 345/35R23. Fit 325/35R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,830 on the road, so it over-counts by 170. At a true 70 mph the first turns 724 times a minute, the second 736.