305/65R17 vs 315/65R17
Going from one to the other changes the overall height by +1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 305/65R17 | 315/65R17 | Change |
|---|---|---|---|
| Overall height | 32.6" | 33.1" | +1.6 % |
| Sidewall | 7.81" | 8.06" | +3.3 % |
| Section width | 305 mm | 315 mm | +3.3 % |
| Circumference | 102.4" | 104.1" | +1.6 % |
| Revs per mile | 618 | 609 | -1.6 % |
| Axle height | 16.31" | 16.56" | +6.5 mm |
| Approved rim width | 8.5–11" | 8.5–11.5" | 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 305/65R17. Fit 315/65R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.1 mph | +1.1 |
| 90 mph | 91.4 mph | +1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,157 on the road, so it under-counts by 157. At a true 70 mph the first turns 722 times a minute, the second 710.
What drivers reported
305/65R17 carries 3 complaints. Nobody has filed one naming 315/65R17.