335/40R23 vs 315/40R23
Going from one to the other changes the overall height by -1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/40R23 | 315/40R23 | Change |
|---|---|---|---|
| Overall height | 33.6" | 32.9" | -1.9 % |
| Sidewall | 5.28" | 4.96" | -6.0 % |
| Section width | 335 mm | 315 mm | -6.0 % |
| Circumference | 105.4" | 103.4" | -1.9 % |
| Revs per mile | 601 | 613 | +1.9 % |
| Axle height | 16.78" | 16.46" | -8.0 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 335/40R23. Fit 315/40R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.7 mph | -1.3 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,812 on the road, so it over-counts by 188. At a true 70 mph the first turns 701 times a minute, the second 715.