245/40R21 tire size

A 245/40R21 tire is 28.72 inches (729.4 mm) tall, 9.65 in (245 mm) wide and fits a 21-inch wheel. In inch notation it is roughly a 28.7x9.6R21 — a "29-inch" tire.

245/40R21 dimensions
Overall diameter	28.72 in	729.4 mm
Section width	9.65 in	245 mm
Sidewall height	3.86 in	98.0 mm
Circumference	90.22 in	2,291 mm
Revolutions	702.3 per mile	436.4 per km
Rim diameter	21 in	533.4 mm

Compare 245/40R21 with another size

Current size

New size

Speed in mphkm/h

Overall diameter difference

−0.48%

60 mph on the speedometer = 59.7 mph actual

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

Ground clearance: −1.8 mm (−0.07 in)
Revolutions: 702 → 706 per mile

245/40R21 275/35R21

Side-by-side dimensions

	Current	New	Difference	%
Diameter	28.72 in	28.58 in	−0.14 in	−0.48%
Diameter	729.4 mm	725.9 mm	−3.5 mm	−0.48%
Width	9.65 in	10.83 in	+1.18 in	+12.24%
Width	245.0 mm	275.0 mm	+30.0 mm	+12.24%
Sidewall	3.86 in	3.79 in	−0.07 in	−1.79%
Sidewall	98.0 mm	96.3 mm	−1.8 mm	−1.79%
Circumference	90.22 in	89.78 in	−0.43 in	−0.48%
Revs per mile	702.3	705.7	+3.4	+0.48%

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	39.8 mph	−0.2 mph
50 mph	49.8 mph	−0.2 mph
60 mph	59.7 mph	−0.3 mph
70 mph	69.7 mph	−0.3 mph
80 mph	79.6 mph	−0.4 mph

Alternative sizes on the same 21-inch wheel

Sizes in use within ±3 % of the overall diameter of 245/40R21:

Plus and minus sizes for 245/40R21

Size	Wheel	Diameter	Difference
225/55R19	Minus 2 (19 in)	28.74 in	+0.10%
275/45R19	Minus 2 (19 in)	28.74 in	+0.10%
245/50R19	Minus 2 (19 in)	28.65 in	−0.25%
255/50R19	Minus 2 (19 in)	29.04 in	+1.12%
245/45R20	Minus 1 (20 in)	28.68 in	−0.12%
275/40R20	Minus 1 (20 in)	28.66 in	−0.19%
285/40R20	Minus 1 (20 in)	28.98 in	+0.90%
255/45R20	Minus 1 (20 in)	29.04 in	+1.11%
285/30R22	Plus 1 (22 in)	28.73 in	+0.05%
295/30R22	Plus 1 (22 in)	28.97 in	+0.88%
255/35R22	Plus 1 (22 in)	29.03 in	+1.08%
265/35R22	Plus 1 (22 in)	29.30 in	+2.04%

Vehicles approved with 245/40R21 tires

Models whose Swiss type approval lists 245/40R21 as a standard or optional size (1,875 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 21-inch sizes

Reading the 245/40R21 size

245 — section width in millimetres (9.65 in).
40 — aspect ratio: the sidewall is 40 % of the width, 98.0 mm.
R — radial construction (ZR on the sidewall means a high-speed rated radial; the dimensions are the same).
21 — fits a 21-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.