30x9.50R15 vs 245/70R17

245/70R17 is 0.50 in (12.8 mm) taller than 30x9.50R15, a +1.68% diameter difference. With the speedometer set for 30x9.50R15, an indicated 60 mph is 61.0 mph on 245/70R17.

Is this a safe swap?

Diameter difference +1.68%: within the ±3% guideline

By overall diameter alone, 245/70R17 falls inside the ±3% range commonly used as a guideline when replacing 30x9.50R15. 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.

30x9.50R15 vs 245/70R17 differences
Measurement	30x9.50R15	245/70R17	Difference	% diff
Overall diameter	30.00 in (762.0 mm)	30.50 in (774.8 mm)	+0.50 in (+12.8 mm)	+1.68%
Sidewall height	7.50 in (190.5 mm)	6.75 in (171.5 mm)	−0.75 in (−19.0 mm)	−9.97%
Section width	9.50 in (241.3 mm)	9.65 in (245.0 mm)	+0.15 in (+3.7 mm)	+1.53%
Circumference	94.25 in (2,393.9 mm)	95.83 in (2,434.1 mm)	+1.58 in (+40.2 mm)	+1.68%
Revolutions per mile	672	661	−11	−1.65%

True speed with the speedometer calibrated for 30x9.50R15
Indicated	Actual on 30x9.50R15	Actual on 245/70R17	Difference
30 mph	30.0 mph	30.5 mph	+0.5 mph
60 mph	60.0 mph	61.0 mph	+1.0 mph
75 mph	75.0 mph	76.3 mph	+1.3 mph

Ride-height change: 245/70R17 raises the vehicle by 0.25 in (6.4 mm) at the axle (half the +12.8 mm diameter difference).

245/70R17 is 0.50 in taller than 30x9.50R15 and 4 mm wider, a 1.68% difference in overall diameter.

With the speedometer calibrated for 30x9.50R15, an indicated 60 mph is actually 61.0 mph on 245/70R17, and revolutions per mile change from 672 to 661.

245/70R17 mounts on a 17-inch wheel, a plus-2 fitment from the 15-inch wheel of 30x9.50R15.

Size pages

Other comparisons with 30x9.50R15

Other comparisons with 245/70R17

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