345/50R23 vs 325/55R23
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 | 345/50R23 | 325/55R23 | Change |
|---|---|---|---|
| Overall height | 36.6" | 37.1" | +1.3 % |
| Sidewall | 6.79" | 7.04" | +3.6 % |
| Section width | 345 mm | 325 mm | -5.8 % |
| Circumference | 114.9" | 116.5" | +1.3 % |
| Revs per mile | 551 | 544 | -1.3 % |
| Axle height | 18.29" | 18.54" | +6.3 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 345/50R23. Fit 325/55R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 70.9 mph | +0.9 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,135 on the road, so it under-counts by 135. At a true 70 mph the first turns 643 times a minute, the second 635.