235/75R15 vs 30x9.50R15

30x9.50R15 is 1.12 in (28.5 mm) taller than 235/75R15, a +3.89% diameter difference. With the speedometer set for 235/75R15, an indicated 60 mph is 62.3 mph on 30x9.50R15.

Is this a safe swap?

Diameter difference +3.89%: outside the ±3% guideline

By overall diameter alone, 30x9.50R15 falls outside the ±3% range commonly used as a guideline when replacing 235/75R15; 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.

235/75R15 vs 30x9.50R15 differences
Measurement	235/75R15	30x9.50R15	Difference	% diff
Overall diameter	28.88 in (733.5 mm)	30.00 in (762.0 mm)	+1.12 in (+28.5 mm)	+3.89%
Sidewall height	6.94 in (176.3 mm)	7.50 in (190.5 mm)	+0.56 in (+14.3 mm)	+8.09%
Section width	9.25 in (235.0 mm)	9.50 in (241.3 mm)	+0.25 in (+6.3 mm)	+2.68%
Circumference	90.72 in (2,304.4 mm)	94.25 in (2,393.9 mm)	+3.53 in (+89.5 mm)	+3.89%
Revolutions per mile	698	672	−26	−3.74%

True speed with the speedometer calibrated for 235/75R15
Indicated	Actual on 235/75R15	Actual on 30x9.50R15	Difference
30 mph	30.0 mph	31.2 mph	+1.2 mph
60 mph	60.0 mph	62.3 mph	+2.3 mph
75 mph	75.0 mph	77.9 mph	+2.9 mph

Ride-height change: 30x9.50R15 raises the vehicle by 0.56 in (14.3 mm) at the axle (half the +28.5 mm diameter difference).

30x9.50R15 is 1.12 in taller than 235/75R15 and 6 mm wider, a 3.89% difference in overall diameter.

With the speedometer calibrated for 235/75R15, an indicated 60 mph is actually 62.3 mph on 30x9.50R15, and revolutions per mile change from 698 to 672.

Both sizes mount on 15-inch wheels.

Size pages

Other comparisons with 235/75R15

Other comparisons with 30x9.50R15

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