325/55R23 vs 345/50R23
Going from one to the other changes the overall height by -1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/55R23 | 345/50R23 | Change |
|---|---|---|---|
| Overall height | 37.1" | 36.6" | -1.3 % |
| Sidewall | 7.04" | 6.79" | -3.5 % |
| Section width | 325 mm | 345 mm | +6.2 % |
| Circumference | 116.5" | 114.9" | -1.3 % |
| Revs per mile | 544 | 551 | +1.3 % |
| Axle height | 18.54" | 18.29" | -6.3 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 325/55R23. Fit 345/50R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.1 mph | -0.9 |
| 90 mph | 88.8 mph | -1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,867 on the road, so it over-counts by 133. At a true 70 mph the first turns 635 times a minute, the second 643.