305/60R17 vs 325/55R17
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 | 305/60R17 | 325/55R17 | Change |
|---|---|---|---|
| Overall height | 31.4" | 31.1" | -1.1 % |
| Sidewall | 7.20" | 7.04" | -2.3 % |
| Section width | 305 mm | 325 mm | +6.6 % |
| Circumference | 98.7" | 97.6" | -1.1 % |
| Revs per mile | 642 | 649 | +1.1 % |
| Axle height | 15.70" | 15.54" | -4.3 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 305/60R17. Fit 325/55R17 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 | 69.3 mph | -0.7 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,893 on the road, so it over-counts by 107. At a true 70 mph the first turns 749 times a minute, the second 757.