235/55R17 vs 295/40R18

295/40R18 is 0.11 in (2.9 mm) taller than 235/55R17, a +0.42% diameter difference. With the speedometer set for 235/55R17, an indicated 60 mph is 60.3 mph on 295/40R18.

Is this a safe swap?

Diameter difference +0.42%: under 1%

By overall diameter alone, 295/40R18 is a near match for 235/55R17; 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.

235/55R17 vs 295/40R18 differences
Measurement	235/55R17	295/40R18	Difference	% diff
Overall diameter	27.18 in (690.3 mm)	27.29 in (693.2 mm)	+0.11 in (+2.9 mm)	+0.42%
Sidewall height	5.09 in (129.3 mm)	4.65 in (118.0 mm)	−0.44 in (−11.2 mm)	−8.70%
Section width	9.25 in (235.0 mm)	11.61 in (295.0 mm)	+2.36 in (+60.0 mm)	+25.53%
Circumference	85.38 in (2,168.6 mm)	85.74 in (2,177.8 mm)	+0.36 in (+9.1 mm)	+0.42%
Revolutions per mile	742	739	−3	−0.42%

True speed with the speedometer calibrated for 235/55R17
Indicated	Actual on 235/55R17	Actual on 295/40R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.3 mph	+0.3 mph
75 mph	75.0 mph	75.3 mph	+0.3 mph

Ride-height change: 295/40R18 raises the vehicle by 0.06 in (1.5 mm) at the axle (half the +2.9 mm diameter difference).

295/40R18 is 0.11 in taller than 235/55R17 and 60 mm wider, a 0.42% difference in overall diameter.

With the speedometer calibrated for 235/55R17, an indicated 60 mph is actually 60.3 mph on 295/40R18, and revolutions per mile change from 742 to 739.

295/40R18 mounts on a 18-inch wheel, a plus-1 fitment from the 17-inch wheel of 235/55R17.

Size pages

Other comparisons with 235/55R17

Other comparisons with 295/40R18

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