335/30R19 vs 315/30R19
Going from one to the other changes the overall height by -1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/30R19 | 315/30R19 | Change |
|---|---|---|---|
| Overall height | 26.9" | 26.4" | -1.8 % |
| Sidewall | 3.96" | 3.72" | -6.0 % |
| Section width | 335 mm | 315 mm | -6.0 % |
| Circumference | 84.6" | 83.1" | -1.8 % |
| Revs per mile | 749 | 763 | +1.8 % |
| Axle height | 13.46" | 13.22" | -6.0 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 335/30R19. Fit 315/30R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.4 mph | -1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,824 on the road, so it over-counts by 176. At a true 70 mph the first turns 874 times a minute, the second 890.