235/60R18 vs 295/40R20

295/40R20 is 0.19 in (4.8 mm) taller than 235/60R18, a +0.65% diameter difference. With the speedometer set for 235/60R18, an indicated 60 mph is 60.4 mph on 295/40R20.

Is this a safe swap?

Diameter difference +0.65%: under 1%

By overall diameter alone, 295/40R20 is a near match for 235/60R18; the speedometer changes by less than 1%. 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.

235/60R18 vs 295/40R20 differences
Measurement	235/60R18	295/40R20	Difference	% diff
Overall diameter	29.10 in (739.2 mm)	29.29 in (744.0 mm)	+0.19 in (+4.8 mm)	+0.65%
Sidewall height	5.55 in (141.0 mm)	4.65 in (118.0 mm)	−0.91 in (−23.0 mm)	−16.31%
Section width	9.25 in (235.0 mm)	11.61 in (295.0 mm)	+2.36 in (+60.0 mm)	+25.53%
Circumference	91.43 in (2,322.3 mm)	92.02 in (2,337.3 mm)	+0.59 in (+15.1 mm)	+0.65%
Revolutions per mile	693	689	−4	−0.65%

True speed with the speedometer calibrated for 235/60R18
Indicated	Actual on 235/60R18	Actual on 295/40R20	Difference
30 mph	30.0 mph	30.2 mph	+0.2 mph
60 mph	60.0 mph	60.4 mph	+0.4 mph
75 mph	75.0 mph	75.5 mph	+0.5 mph

Ride-height change: 295/40R20 raises the vehicle by 0.09 in (2.4 mm) at the axle (half the +4.8 mm diameter difference).

295/40R20 is 0.19 in taller than 235/60R18 and 60 mm wider, a 0.65% difference in overall diameter.

With the speedometer calibrated for 235/60R18, an indicated 60 mph is actually 60.4 mph on 295/40R20, and revolutions per mile change from 693 to 689.

295/40R20 mounts on a 20-inch wheel, a plus-2 fitment from the 18-inch wheel of 235/60R18.

Size pages

Other comparisons with 235/60R18

Other comparisons with 295/40R20

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