275/45R18 tire size

A 275/45R18 tire is 27.74 inches (704.7 mm) tall, 10.83 in (275 mm) wide and fits a 18-inch wheel. In inch notation it is roughly a 27.7x10.8R18 — a "28-inch" tire.

275/45R18 dimensions
Overall diameter	27.74 in	704.7 mm
Section width	10.83 in	275 mm
Sidewall height	4.87 in	123.8 mm
Circumference	87.16 in	2,214 mm
Revolutions	726.9 per mile	451.7 per km
Rim diameter	18 in	457.2 mm

Compare 275/45R18 with another size

Current size

New size

Speed in mphkm/h

Overall diameter difference

−0.35%

60 mph on the speedometer = 59.8 mph actual

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

Ground clearance: −1.3 mm (−0.05 in)
Revolutions: 727 → 730 per mile

275/45R18 245/50R18

Side-by-side dimensions

	Current	New	Difference	%
Diameter	27.74 in	27.65 in	−0.10 in	−0.35%
Diameter	704.7 mm	702.2 mm	−2.5 mm	−0.35%
Width	10.83 in	9.65 in	−1.18 in	−10.91%
Width	275.0 mm	245.0 mm	−30.0 mm	−10.91%
Sidewall	4.87 in	4.82 in	−0.05 in	−1.01%
Sidewall	123.8 mm	122.5 mm	−1.3 mm	−1.01%
Circumference	87.16 in	86.85 in	−0.31 in	−0.35%
Revs per mile	726.9	729.5	+2.6	+0.36%

Speedometer error

Speedometer shows	Actual speed	Difference
20 mph	19.9 mph	−0.1 mph
30 mph	29.9 mph	−0.1 mph
40 mph	39.9 mph	−0.1 mph
50 mph	49.8 mph	−0.2 mph
60 mph	59.8 mph	−0.2 mph
70 mph	69.8 mph	−0.2 mph
80 mph	79.7 mph	−0.3 mph

Alternative sizes on the same 18-inch wheel

Sizes in use within ±3 % of the overall diameter of 275/45R18:

Plus and minus sizes for 275/45R18

Size	Wheel	Diameter	Difference
245/60R16	Minus 2 (16 in)	27.57 in	−0.61%
245/55R17	Minus 1 (17 in)	27.61 in	−0.48%
255/55R17	Minus 1 (17 in)	28.04 in	+1.08%
245/45R19	Plus 1 (19 in)	27.68 in	−0.23%
275/40R19	Plus 1 (19 in)	27.66 in	−0.30%
285/40R19	Plus 1 (19 in)	27.98 in	+0.84%
255/45R19	Plus 1 (19 in)	28.04 in	+1.05%
245/40R20	Plus 2 (20 in)	27.72 in	−0.10%
325/30R20	Plus 2 (20 in)	27.68 in	−0.24%
285/35R20	Plus 2 (20 in)	27.85 in	+0.40%
275/35R20	Plus 2 (20 in)	27.58 in	−0.60%
245/35R21	Plus 3 (21 in)	27.75 in	+0.03%
285/30R21	Plus 3 (21 in)	27.73 in	−0.04%
295/30R21	Plus 3 (21 in)	27.97 in	+0.81%
275/30R21	Plus 3 (21 in)	27.50 in	−0.89%

Vehicles approved with 275/45R18 tires

Models whose Swiss type approval lists 275/45R18 as a standard or optional size (256 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 275/45R18 size

275 — section width in millimetres (10.83 in).
45 — aspect ratio: the sidewall is 45 % of the width, 123.8 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.