305/55R23 vs 325/50R23
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 | 305/55R23 | 325/50R23 | Change |
|---|---|---|---|
| Overall height | 36.2" | 35.8" | -1.1 % |
| Sidewall | 6.60" | 6.40" | -3.1 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 113.8" | 112.5" | -1.1 % |
| Revs per mile | 557 | 563 | +1.1 % |
| Axle height | 18.10" | 17.90" | -5.3 mm |
| Approved rim width | 8.5–11" | 9–12" | overlap 9–11" |
Both are approved on a rim 9" to 11" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 305/55R23. Fit 325/50R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.4 mph | -0.6 |
| 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 9,886 on the road, so it over-counts by 114. At a true 70 mph the first turns 650 times a minute, the second 657.