325/60R23 vs 345/55R23
Going from one to the other changes the overall height by -1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/60R23 | 345/55R23 | Change |
|---|---|---|---|
| Overall height | 38.4" | 37.9" | -1.1 % |
| Sidewall | 7.68" | 7.47" | -2.7 % |
| Section width | 325 mm | 345 mm | +6.2 % |
| Circumference | 120.5" | 119.2" | -1.1 % |
| Revs per mile | 526 | 532 | +1.1 % |
| Axle height | 19.18" | 18.97" | -5.3 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 325/60R23. Fit 345/55R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.5 mph | -0.5 |
| 70 mph | 69.2 mph | -0.8 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,892 on the road, so it over-counts by 108. At a true 70 mph the first turns 613 times a minute, the second 620.