295/45R17 vs 315/40R17
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 | 295/45R17 | 315/40R17 | Change |
|---|---|---|---|
| Overall height | 27.5" | 26.9" | -1.9 % |
| Sidewall | 5.23" | 4.96" | -5.1 % |
| Section width | 295 mm | 315 mm | +6.8 % |
| Circumference | 86.2" | 84.6" | -1.9 % |
| Revs per mile | 735 | 749 | +1.9 % |
| Axle height | 13.73" | 13.46" | -6.8 mm |
| Approved rim width | 8.5–11" | 8.5–11.5" | overlap 8.5–11" |
Both are approved on a rim 8.5" to 11" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 295/45R17. Fit 315/40R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.0 mph | -1.0 |
| 70 mph | 68.6 mph | -1.4 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,806 on the road, so it over-counts by 194. At a true 70 mph the first turns 857 times a minute, the second 874.