315/75R17 vs 295/70R18

295/70R18 is 1.34 in (34.1 mm) shorter than 315/75R17, a −3.77% diameter difference. With the speedometer set for 315/75R17, an indicated 60 mph is 57.7 mph on 295/70R18.

Is this a safe swap?

Diameter difference −3.77%: outside the ±3% guideline

By overall diameter alone, 295/70R18 falls outside the ±3% range commonly used as a guideline when replacing 315/75R17; speedometer and ride-height changes are larger. This check uses diameter only. It does not assess load index, speed rating, wheel width or clearance.

Side profile and tread width, drawn to the same scale.

315/75R17 vs 295/70R18 differences
Measurement	315/75R17	295/70R18	Difference	% diff
Overall diameter	35.60 in (904.3 mm)	34.26 in (870.2 mm)	−1.34 in (−34.1 mm)	−3.77%
Sidewall height	9.30 in (236.3 mm)	8.13 in (206.5 mm)	−1.17 in (−29.7 mm)	−12.59%
Section width	12.40 in (315.0 mm)	11.61 in (295.0 mm)	−0.79 in (−20.0 mm)	−6.35%
Circumference	111.85 in (2,840.9 mm)	107.63 in (2,733.8 mm)	−4.22 in (−107.1 mm)	−3.77%
Revolutions per mile	566	589	+22	+3.92%

True speed with the speedometer calibrated for 315/75R17
Indicated	Actual on 315/75R17	Actual on 295/70R18	Difference
30 mph	30.0 mph	28.9 mph	−1.1 mph
60 mph	60.0 mph	57.7 mph	−2.3 mph
75 mph	75.0 mph	72.2 mph	−2.8 mph

Ride-height change: 295/70R18 lowers the vehicle by 0.67 in (17.0 mm) at the axle (half the −34.1 mm diameter difference).

295/70R18 is 1.34 in shorter than 315/75R17 and 20 mm narrower, a 3.77% difference in overall diameter.

With the speedometer calibrated for 315/75R17, an indicated 60 mph is actually 57.7 mph on 295/70R18, and revolutions per mile change from 566 to 589.

295/70R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 315/75R17.

Size pages

Other comparisons with 315/75R17

Other comparisons with 295/70R18

Source: Calculated from standard tire geometry formulas. Verified 2026-09-27. How these numbers are calculated.