235/50R18 vs 295/30R20

295/30R20 is 0.28 in (7.2 mm) shorter than 235/50R18, a −1.04% diameter difference. With the speedometer set for 235/50R18, an indicated 60 mph is 59.4 mph on 295/30R20.

Is this a safe swap?

Diameter difference −1.04%: within the ±3% guideline

By overall diameter alone, 295/30R20 falls inside the ±3% range commonly used as a guideline when replacing 235/50R18. 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.

235/50R18 vs 295/30R20 differences
Measurement	235/50R18	295/30R20	Difference	% diff
Overall diameter	27.25 in (692.2 mm)	26.97 in (685.0 mm)	−0.28 in (−7.2 mm)	−1.04%
Sidewall height	4.63 in (117.5 mm)	3.48 in (88.5 mm)	−1.14 in (−29.0 mm)	−24.68%
Section width	9.25 in (235.0 mm)	11.61 in (295.0 mm)	+2.36 in (+60.0 mm)	+25.53%
Circumference	85.61 in (2,174.6 mm)	84.72 in (2,152.0 mm)	−0.89 in (−22.6 mm)	−1.04%
Revolutions per mile	740	748	+8	+1.05%

True speed with the speedometer calibrated for 235/50R18
Indicated	Actual on 235/50R18	Actual on 295/30R20	Difference
30 mph	30.0 mph	29.7 mph	−0.3 mph
60 mph	60.0 mph	59.4 mph	−0.6 mph
75 mph	75.0 mph	74.2 mph	−0.8 mph

Ride-height change: 295/30R20 lowers the vehicle by 0.14 in (3.6 mm) at the axle (half the −7.2 mm diameter difference).

295/30R20 is 0.28 in shorter than 235/50R18 and 60 mm wider, a 1.04% difference in overall diameter.

With the speedometer calibrated for 235/50R18, an indicated 60 mph is actually 59.4 mph on 295/30R20, and revolutions per mile change from 740 to 748.

295/30R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 235/50R18.

Size pages

Other comparisons with 235/50R18

Other comparisons with 295/30R20

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