285/70R17 vs 315/70R17: full comparison
| Measurement | 285/70R17 | 315/70R17 | Difference |
|---|---|---|---|
| Diameter | 32.71 in | 34.36 in | +1.65 in+5.1% |
| Section width | 11.22 in | 12.40 in | +1.18 in+10.5% |
| Sidewall height | 7.85 in | 8.68 in | +0.83 in+10.5% |
| Circumference | 102.76 in | 107.95 in | +5.19 in+5.1% |
| Revs per mile | 617 | 587 | −30−4.8% |
Speedometer: indicated vs actual speed
With 315/70R17 fitted where 285/70R17 was the stock/calibrated size:
| Speedometer shows | Actual speed | Difference |
|---|---|---|
| 20 mph | 21.0 mph | +1.0 mph |
| 30 mph | 31.5 mph | +1.5 mph |
| 40 mph | 42.0 mph | +2.0 mph |
| 50 mph | 52.5 mph | +2.5 mph |
| 55 mph | 57.8 mph | +2.8 mph |
| 60 mph | 63.0 mph | +3.0 mph |
| 65 mph | 68.3 mph | +3.3 mph |
| 70 mph | 73.5 mph | +3.5 mph |
| 75 mph | 78.8 mph | +3.8 mph |
| 80 mph | 84.0 mph | +4.0 mph |
Recalculate for a gear ratio change too →
Will 315/70R17 fit where 285/70R17 was?
At +5.1%, 315/70R17 is enough larger than 285/70R17 that it commonly needs some accommodation -- trimming plastic liners/fender edges, a spacer, or a leveling kit on trucks/SUVs going bigger. Check clearance at full steering lock and full suspension compression before buying.
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Frequently asked questions
How much bigger is 315/70R17 than 285/70R17?
315/70R17 is 1.65 in taller in overall diameter (+5.1%) and 1.18 in wider in section width (+10.5%) than 285/70R17.
Will 315/70R17 fit in place of 285/70R17?
At +5.1%, 315/70R17 is enough larger than 285/70R17 that it commonly needs some accommodation -- trimming plastic liners/fender edges, a spacer, or a leveling kit on trucks/SUVs going bigger. Check clearance at full steering lock and full suspension compression before buying.
Does swapping to 315/70R17 affect my speedometer?
With 315/70R17 fitted where 285/70R17 was calibrated, an indicated 60 mph is really about 63.0 mph. Beyond the ±3% guideline, plan to recalibrate the speedometer/odometer (with a programmer or at the dealer) for an accurate reading.
Does 315/70R17 change the ride height?
Yes -- half the diameter difference shows up at the axle, so 315/70R17 changes ride height by about 0.83 in higher compared with 285/70R17.
Do 285/70R17 and 315/70R17 use the same wheel (rim) diameter?
Yes -- both fit a 17 inch wheel, so only the tire itself changes, not the wheel.