255/40R18 vs 295/35R18

295/35R18 is 0.10 in (2.5 mm) taller than 255/40R18, a +0.38% diameter difference. With the speedometer set for 255/40R18, an indicated 60 mph is 60.2 mph on 295/35R18.

Is this a safe swap?

Diameter difference +0.38%: under 1%

By overall diameter alone, 295/35R18 is a near match for 255/40R18; 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.

255/40R18 vs 295/35R18 differences
Measurement	255/40R18	295/35R18	Difference	% diff
Overall diameter	26.03 in (661.2 mm)	26.13 in (663.7 mm)	+0.10 in (+2.5 mm)	+0.38%
Sidewall height	4.02 in (102.0 mm)	4.06 in (103.3 mm)	+0.05 in (+1.3 mm)	+1.23%
Section width	10.04 in (255.0 mm)	11.61 in (295.0 mm)	+1.57 in (+40.0 mm)	+15.69%
Circumference	81.78 in (2,077.2 mm)	82.09 in (2,085.1 mm)	+0.31 in (+7.9 mm)	+0.38%
Revolutions per mile	775	772	−3	−0.38%

True speed with the speedometer calibrated for 255/40R18
Indicated	Actual on 255/40R18	Actual on 295/35R18	Difference
30 mph	30.0 mph	30.1 mph	+0.1 mph
60 mph	60.0 mph	60.2 mph	+0.2 mph
75 mph	75.0 mph	75.3 mph	+0.3 mph

Ride-height change: 295/35R18 raises the vehicle by 0.05 in (1.3 mm) at the axle (half the +2.5 mm diameter difference).

295/35R18 is 0.10 in taller than 255/40R18 and 40 mm wider, a 0.38% difference in overall diameter.

With the speedometer calibrated for 255/40R18, an indicated 60 mph is actually 60.2 mph on 295/35R18, and revolutions per mile change from 775 to 772.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 255/40R18

Other comparisons with 295/35R18

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