215/40R18 tire size

A 215/40R18 tire is 24.77 inches (629.2 mm) tall, 8.46 in (215 mm) wide and fits a 18-inch wheel. In inch notation it is roughly a 24.8x8.5R18.

215/40R18 dimensions
Overall diameter	24.77 in	629.2 mm
Section width	8.46 in	215 mm
Sidewall height	3.39 in	86.0 mm
Circumference	77.82 in	1,977 mm
Revolutions	814.2 per mile	505.9 per km
Rim diameter	18 in	457.2 mm

Compare 215/40R18 with another size

Current size

New size

Speed in mphkm/h

Overall diameter difference

−0.08%

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: 814 → 815 per mile

215/40R18 245/35R18

Side-by-side dimensions

	Current	New	Difference	%
Diameter	24.77 in	24.75 in	−0.02 in	−0.08%
Diameter	629.2 mm	628.7 mm	−0.5 mm	−0.08%
Width	8.46 in	9.65 in	+1.18 in	+13.95%
Width	215.0 mm	245.0 mm	+30.0 mm	+13.95%
Sidewall	3.39 in	3.38 in	−0.01 in	−0.29%
Sidewall	86.0 mm	85.8 mm	−0.3 mm	−0.29%
Circumference	77.82 in	77.76 in	−0.06 in	−0.08%
Revs per mile	814.2	814.8	+0.6	+0.08%

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	69.9 mph	−0.1 mph
80 mph	79.9 mph	−0.1 mph

Alternative sizes on the same 18-inch wheel

Sizes in use within ±3 % of the overall diameter of 215/40R18:

Plus and minus sizes for 215/40R18

Size	Wheel	Diameter	Difference
185/60R16	Minus 2 (16 in)	24.74 in	−0.13%
225/50R16	Minus 2 (16 in)	24.86 in	+0.35%
245/45R16	Minus 2 (16 in)	24.68 in	−0.37%
205/55R16	Minus 2 (16 in)	24.88 in	+0.43%
245/40R17	Minus 1 (17 in)	24.72 in	−0.22%
215/45R17	Minus 1 (17 in)	24.62 in	−0.62%
225/45R17	Minus 1 (17 in)	24.97 in	+0.81%
255/40R17	Minus 1 (17 in)	25.03 in	+1.05%
245/30R19	Plus 1 (19 in)	24.79 in	+0.06%
255/30R19	Plus 1 (19 in)	25.02 in	+1.02%
225/35R19	Plus 1 (19 in)	25.20 in	+1.73%
265/30R19	Plus 1 (19 in)	25.26 in	+1.97%

Vehicles approved with 215/40R18 tires

Models whose Swiss type approval lists 215/40R18 as a standard or optional size (765 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 215/40R18 size

215 — section width in millimetres (8.46 in).
40 — aspect ratio: the sidewall is 40 % of the width, 86.0 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.