335/25R17 vs 315/25R17
Going from one to the other changes the overall height by -1.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/25R17 | 315/25R17 | Change |
|---|---|---|---|
| Overall height | 23.6" | 23.2" | -1.7 % |
| Sidewall | 3.30" | 3.10" | -6.0 % |
| Section width | 335 mm | 315 mm | -6.0 % |
| Circumference | 74.1" | 72.9" | -1.7 % |
| Revs per mile | 855 | 869 | +1.7 % |
| Axle height | 11.80" | 11.60" | -5.0 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 335/25R17. Fit 315/25R17 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 | 68.8 mph | -1.2 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,833 on the road, so it over-counts by 167. At a true 70 mph the first turns 997 times a minute, the second 1014.