35x11.50R17 vs 315/70R18

315/70R18 is 0.36 in (9.2 mm) taller than 35x11.50R17, a +1.03% diameter difference. With the speedometer set for 35x11.50R17, an indicated 60 mph is 60.6 mph on 315/70R18.

Is this a safe swap?

Diameter difference +1.03%: within the ±3% guideline

By overall diameter alone, 315/70R18 falls inside the ±3% range commonly used as a guideline when replacing 35x11.50R17. 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.

35x11.50R17 vs 315/70R18 differences
Measurement	35x11.50R17	315/70R18	Difference	% diff
Overall diameter	35.00 in (889.0 mm)	35.36 in (898.2 mm)	+0.36 in (+9.2 mm)	+1.03%
Sidewall height	9.00 in (228.6 mm)	8.68 in (220.5 mm)	−0.32 in (−8.1 mm)	−3.54%
Section width	11.50 in (292.1 mm)	12.40 in (315.0 mm)	+0.90 in (+22.9 mm)	+7.84%
Circumference	109.96 in (2,792.9 mm)	111.09 in (2,821.8 mm)	+1.14 in (+28.9 mm)	+1.03%
Revolutions per mile	576	570	−6	−1.02%

True speed with the speedometer calibrated for 35x11.50R17
Indicated	Actual on 35x11.50R17	Actual on 315/70R18	Difference
30 mph	30.0 mph	30.3 mph	+0.3 mph
60 mph	60.0 mph	60.6 mph	+0.6 mph
75 mph	75.0 mph	75.8 mph	+0.8 mph

Ride-height change: 315/70R18 raises the vehicle by 0.18 in (4.6 mm) at the axle (half the +9.2 mm diameter difference).

315/70R18 is 0.36 in taller than 35x11.50R17 and 23 mm wider, a 1.03% difference in overall diameter.

With the speedometer calibrated for 35x11.50R17, an indicated 60 mph is actually 60.6 mph on 315/70R18, and revolutions per mile change from 576 to 570.

315/70R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 35x11.50R17.

Size pages

Other comparisons with 35x11.50R17

Other comparisons with 315/70R18

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