315/65R17 vs 305/65R17
Going from one to the other changes the overall height by -1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/65R17 | 305/65R17 | Change |
|---|---|---|---|
| Overall height | 33.1" | 32.6" | -1.5 % |
| Sidewall | 8.06" | 7.81" | -3.2 % |
| Section width | 315 mm | 305 mm | -3.2 % |
| Circumference | 104.1" | 102.4" | -1.5 % |
| Revs per mile | 609 | 618 | +1.5 % |
| Axle height | 16.56" | 16.31" | -6.5 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 315/65R17. Fit 305/65R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.9 mph | -1.1 |
| 90 mph | 88.6 mph | -1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,845 on the road, so it over-counts by 155. At a true 70 mph the first turns 710 times a minute, the second 722.
What drivers reported
Nobody has filed a complaint naming 315/65R17. 305/65R17 carries 3.