305/25R17 vs 325/25R17
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 | 305/25R17 | 325/25R17 | Change |
|---|---|---|---|
| Overall height | 23.0" | 23.4" | +1.7 % |
| Sidewall | 3.00" | 3.20" | +6.6 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 72.3" | 73.5" | +1.7 % |
| Revs per mile | 877 | 862 | -1.7 % |
| Axle height | 11.50" | 11.70" | +5.0 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 305/25R17. Fit 325/25R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.2 mph | +1.2 |
| 90 mph | 91.5 mph | +1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,171 on the road, so it under-counts by 171. At a true 70 mph the first turns 1023 times a minute, the second 1006.