335/65R17 vs 315/65R17
Going from one to the other changes the overall height by -3.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/65R17 | 315/65R17 | Change |
|---|---|---|---|
| Overall height | 34.1" | 33.1" | -3.0 % |
| Sidewall | 8.57" | 8.06" | -6.0 % |
| Section width | 335 mm | 315 mm | -6.0 % |
| Circumference | 107.3" | 104.1" | -3.0 % |
| Revs per mile | 591 | 609 | +3.0 % |
| Axle height | 17.07" | 16.56" | -13.0 mm |
| Approved rim width | 9.5–12.5" | 8.5–11.5" | overlap 9.5–11.5" |
Both are approved on a rim 9.5" to 11.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 335/65R17. Fit 315/65R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.5 mph | -1.5 |
| 70 mph | 67.9 mph | -2.1 |
| 90 mph | 87.3 mph | -2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,700 on the road, so it over-counts by 300. At a true 70 mph the first turns 689 times a minute, the second 710.