235/50R18 vs 295/40R18

295/40R18 is 0.04 in (1.0 mm) taller than 235/50R18, a +0.14% diameter difference. With the speedometer set for 235/50R18, an indicated 60 mph is 60.1 mph on 295/40R18.

Is this a safe swap?

Diameter difference +0.14%: under 1%

By overall diameter alone, 295/40R18 is a near match for 235/50R18; 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.

235/50R18 vs 295/40R18 differences
Measurement	235/50R18	295/40R18	Difference	% diff
Overall diameter	27.25 in (692.2 mm)	27.29 in (693.2 mm)	+0.04 in (+1.0 mm)	+0.14%
Sidewall height	4.63 in (117.5 mm)	4.65 in (118.0 mm)	+0.02 in (+0.5 mm)	+0.43%
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)	85.74 in (2,177.8 mm)	+0.12 in (+3.1 mm)	+0.14%
Revolutions per mile	740	739	−1	−0.14%

True speed with the speedometer calibrated for 235/50R18
Indicated	Actual on 235/50R18	Actual on 295/40R18	Difference
30 mph	30.0 mph	30.0 mph	0.0 mph
60 mph	60.0 mph	60.1 mph	+0.1 mph
75 mph	75.0 mph	75.1 mph	+0.1 mph

Ride-height change: 295/40R18 raises the vehicle by 0.02 in (0.5 mm) at the axle (half the +1.0 mm diameter difference).

295/40R18 is 0.04 in taller than 235/50R18 and 60 mm wider, a 0.14% difference in overall diameter.

With the speedometer calibrated for 235/50R18, an indicated 60 mph is actually 60.1 mph on 295/40R18, and revolutions per mile change from 740 to 739.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 235/50R18

Other comparisons with 295/40R18

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