335/45R17 vs 315/50R17
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 | 335/45R17 | 315/50R17 | Change |
|---|---|---|---|
| Overall height | 28.9" | 29.4" | +1.8 % |
| Sidewall | 5.94" | 6.20" | +4.5 % |
| Section width | 335 mm | 315 mm | -6.0 % |
| Circumference | 90.7" | 92.4" | +1.8 % |
| Revs per mile | 699 | 686 | -1.8 % |
| Axle height | 14.44" | 14.70" | +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 335/45R17. Fit 315/50R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,184 on the road, so it under-counts by 184. At a true 70 mph the first turns 815 times a minute, the second 800.