325/60R17 vs 305/65R17
Going from one to the other changes the overall height by +0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 325/60R17 | 305/65R17 | Change |
|---|---|---|---|
| Overall height | 32.4" | 32.6" | +0.8 % |
| Sidewall | 7.68" | 7.81" | +1.7 % |
| Section width | 325 mm | 305 mm | -6.2 % |
| Circumference | 101.6" | 102.4" | +0.8 % |
| Revs per mile | 623 | 618 | -0.8 % |
| Axle height | 16.18" | 16.31" | +3.3 mm |
| Approved rim width | 9–12" | 8.5–11" | 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 325/60R17. Fit 305/65R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.6 mph | +0.6 |
| 90 mph | 90.7 mph | +0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,079 on the road, so it under-counts by 79. At a true 70 mph the first turns 727 times a minute, the second 722.
What drivers reported
Nobody has filed a complaint naming 325/60R17. 305/65R17 carries 3.