295/35R17 vs 315/30R17
Going from one to the other changes the overall height by -2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 295/35R17 | 315/30R17 | Change |
|---|---|---|---|
| Overall height | 25.1" | 24.4" | -2.7 % |
| Sidewall | 4.06" | 3.72" | -8.5 % |
| Section width | 295 mm | 315 mm | +6.8 % |
| Circumference | 78.9" | 76.8" | -2.7 % |
| Revs per mile | 803 | 825 | +2.7 % |
| Axle height | 12.56" | 12.22" | -8.8 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 295/35R17. Fit 315/30R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.1 mph | -1.9 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,726 on the road, so it over-counts by 274. At a true 70 mph the first turns 936 times a minute, the second 963.