235/65R18 tire size

A 235/65R18 tire is 30.03 inches (762.7 mm) tall, 9.25 in (235 mm) wide and fits a 18-inch wheel. In inch notation it is roughly a 30.0x9.3R18 — a "30-inch" tire.

235/65R18 dimensions
Overall diameter	30.03 in	762.7 mm
Section width	9.25 in	235 mm
Sidewall height	6.01 in	152.8 mm
Circumference	94.33 in	2,396 mm
Revolutions	671.7 per mile	417.3 per km
Rim diameter	18 in	457.2 mm

Compare 235/65R18 with another size

Current size

New size

Speed in mphkm/h

Overall diameter difference

+0.07%

60 mph on the speedometer = 60.0 mph actual

Within the ±3 % diameter range most tire fitters accept.

Ground clearance: +0.3 mm (+0.01 in)
Revolutions: 672 → 671 per mile

235/65R18 255/60R18

Side-by-side dimensions

	Current	New	Difference	%
Diameter	30.03 in	30.05 in	+0.02 in	+0.07%
Diameter	762.7 mm	763.2 mm	+0.5 mm	+0.07%
Width	9.25 in	10.04 in	+0.79 in	+8.51%
Width	235.0 mm	255.0 mm	+20.0 mm	+8.51%
Sidewall	6.01 in	6.02 in	+0.01 in	+0.16%
Sidewall	152.8 mm	153.0 mm	+0.3 mm	+0.16%
Circumference	94.33 in	94.40 in	+0.06 in	+0.07%
Revs per mile	671.7	671.2	−0.4	−0.07%

Speedometer error

Speedometer shows	Actual speed	Difference
20 mph	20.0 mph	0.0 mph
30 mph	30.0 mph	0.0 mph
40 mph	40.0 mph	0.0 mph
50 mph	50.0 mph	0.0 mph
60 mph	60.0 mph	0.0 mph
70 mph	70.0 mph	0.0 mph
80 mph	80.1 mph	+0.1 mph

Alternative sizes on the same 18-inch wheel

Sizes in use within ±3 % of the overall diameter of 235/65R18:

Plus and minus sizes for 235/65R18

Size	Wheel	Diameter	Difference
255/70R16	Minus 2 (16 in)	30.06 in	+0.09%
235/75R16	Minus 2 (16 in)	29.88 in	−0.50%
245/75R16	Minus 2 (16 in)	30.47 in	+1.47%
215/80R16	Minus 2 (16 in)	29.54 in	−1.61%
255/65R17	Minus 1 (17 in)	30.05 in	+0.08%
235/70R17	Minus 1 (17 in)	29.95 in	−0.25%
245/70R17	Minus 1 (17 in)	30.50 in	+1.59%
245/65R17	Minus 1 (17 in)	29.54 in	−1.63%
255/55R19	Plus 1 (19 in)	30.04 in	+0.05%
235/60R19	Plus 1 (19 in)	30.10 in	+0.25%
275/50R19	Plus 1 (19 in)	29.83 in	−0.67%
265/55R19	Plus 1 (19 in)	30.48 in	+1.49%
255/50R20	Plus 2 (20 in)	30.04 in	+0.04%
285/45R20	Plus 2 (20 in)	30.10 in	+0.24%
235/55R20	Plus 2 (20 in)	30.18 in	+0.50%
275/45R20	Plus 2 (20 in)	29.74 in	−0.94%
255/45R21	Plus 3 (21 in)	30.04 in	+0.03%
285/40R21	Plus 3 (21 in)	29.98 in	−0.17%
235/50R21	Plus 3 (21 in)	30.25 in	+0.75%
245/45R21	Plus 3 (21 in)	29.68 in	−1.15%

Vehicles approved with 235/65R18 tires

Models whose Swiss type approval lists 235/65R18 as a standard or optional size (400 approvals in total). Always check your own vehicle's placard or papers.

Source: Swiss Federal Roads Office (FEDRO/ASTRA), open government data. Original data (downloaded 2026-09-29). Data processed by us; errors in processing are ours, not the publisher's.

Nearby 18-inch sizes

Reading the 235/65R18 size

235 — section width in millimetres (9.25 in).
65 — aspect ratio: the sidewall is 65 % of the width, 152.8 mm.
R — radial construction (ZR on the sidewall means a high-speed rated radial; the dimensions are the same).
18 — fits a 18-inch diameter wheel.

The load index and speed rating (for example 91V) follow the size on the sidewall. They must meet at least the values on your vehicle's tire placard.