215/35R18 vs 235/35R18

235/35R18 is 0.55 in (14.0 mm) taller than 215/35R18, a +2.30% diameter difference. With the speedometer set for 215/35R18, an indicated 60 mph is 61.4 mph on 235/35R18.

Is this a safe swap?

Diameter difference +2.30%: within the ±3% guideline

By overall diameter alone, 235/35R18 falls inside the ±3% range commonly used as a guideline when replacing 215/35R18. 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.

215/35R18 vs 235/35R18 differences
Measurement	215/35R18	235/35R18	Difference	% diff
Overall diameter	23.93 in (607.7 mm)	24.48 in (621.7 mm)	+0.55 in (+14.0 mm)	+2.30%
Sidewall height	2.96 in (75.3 mm)	3.24 in (82.3 mm)	+0.28 in (+7.0 mm)	+9.30%
Section width	8.46 in (215.0 mm)	9.25 in (235.0 mm)	+0.79 in (+20.0 mm)	+9.30%
Circumference	75.16 in (1,909.1 mm)	76.89 in (1,953.1 mm)	+1.73 in (+44.0 mm)	+2.30%
Revolutions per mile	843	824	−19	−2.25%

True speed with the speedometer calibrated for 215/35R18
Indicated	Actual on 215/35R18	Actual on 235/35R18	Difference
30 mph	30.0 mph	30.7 mph	+0.7 mph
60 mph	60.0 mph	61.4 mph	+1.4 mph
75 mph	75.0 mph	76.7 mph	+1.7 mph

Ride-height change: 235/35R18 raises the vehicle by 0.28 in (7.0 mm) at the axle (half the +14.0 mm diameter difference).

235/35R18 is 0.55 in taller than 215/35R18 and 20 mm wider, a 2.30% difference in overall diameter.

With the speedometer calibrated for 215/35R18, an indicated 60 mph is actually 61.4 mph on 235/35R18, and revolutions per mile change from 843 to 824.

Both sizes mount on 18-inch wheels.

Size pages

Other comparisons with 215/35R18

Other comparisons with 235/35R18

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