315/60R17 vs 305/65R17
Going from one to the other changes the overall height by +2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/60R17 | 305/65R17 | Change |
|---|---|---|---|
| Overall height | 31.9" | 32.6" | +2.3 % |
| Sidewall | 7.44" | 7.81" | +4.9 % |
| Section width | 315 mm | 305 mm | -3.2 % |
| Circumference | 100.2" | 102.4" | +2.3 % |
| Revs per mile | 633 | 618 | -2.3 % |
| Axle height | 15.94" | 16.31" | +9.3 mm |
| Approved rim width | 8.5–11.5" | 8.5–11" | overlap 8.5–11" |
Both are approved on a rim 8.5" to 11" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 315/60R17. Fit 305/65R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.6 mph | +1.6 |
| 90 mph | 92.1 mph | +2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,228 on the road, so it under-counts by 228. At a true 70 mph the first turns 738 times a minute, the second 722.
What drivers reported
Nobody has filed a complaint naming 315/60R17. 305/65R17 carries 3.