335/45R23 vs 315/50R23
Going from one to the other changes the overall height by +1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/45R23 | 315/50R23 | Change |
|---|---|---|---|
| Overall height | 34.9" | 35.4" | +1.5 % |
| Sidewall | 5.94" | 6.20" | +4.5 % |
| Section width | 335 mm | 315 mm | -6.0 % |
| Circumference | 109.5" | 111.2" | +1.5 % |
| Revs per mile | 578 | 570 | -1.5 % |
| Axle height | 17.44" | 17.70" | +6.8 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 335/45R23. Fit 315/50R23 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 10,152 on the road, so it under-counts by 152. At a true 70 mph the first turns 675 times a minute, the second 665.