255/35R21 tire size

A 255/35R21 tire is 28.03 inches (711.9 mm) tall, 10.04 in (255 mm) wide and fits a 21-inch wheel. In inch notation it is roughly a 28.0x10.0R21 — a "28-inch" tire.

255/35R21 dimensions
Overall diameter	28.03 in	711.9 mm
Section width	10.04 in	255 mm
Sidewall height	3.51 in	89.3 mm
Circumference	88.05 in	2,236 mm
Revolutions	719.6 per mile	447.1 per km
Rim diameter	21 in	533.4 mm

Compare 255/35R21 with another size

Current size

New size

Speed in mphkm/h

Overall diameter difference

−0.21%

60 mph on the speedometer = 59.9 mph actual

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

Ground clearance: −0.8 mm (−0.03 in)
Revolutions: 720 → 721 per mile

255/35R21 295/30R21

Side-by-side dimensions

	Current	New	Difference	%
Diameter	28.03 in	27.97 in	−0.06 in	−0.21%
Diameter	711.9 mm	710.4 mm	−1.5 mm	−0.21%
Width	10.04 in	11.61 in	+1.57 in	+15.69%
Width	255.0 mm	295.0 mm	+40.0 mm	+15.69%
Sidewall	3.51 in	3.48 in	−0.03 in	−0.84%
Sidewall	89.3 mm	88.5 mm	−0.8 mm	−0.84%
Circumference	88.05 in	87.87 in	−0.19 in	−0.21%
Revs per mile	719.6	721.1	+1.5	+0.21%

Speedometer error

Speedometer shows	Actual speed	Difference
20 mph	20.0 mph	0.0 mph
30 mph	29.9 mph	−0.1 mph
40 mph	39.9 mph	−0.1 mph
50 mph	49.9 mph	−0.1 mph
60 mph	59.9 mph	−0.1 mph
70 mph	69.9 mph	−0.1 mph
80 mph	79.8 mph	−0.2 mph

Alternative sizes on the same 21-inch wheel

Sizes in use within ±3 % of the overall diameter of 255/35R21:

Plus and minus sizes for 255/35R21

Size	Wheel	Diameter	Difference
255/45R19	Minus 2 (19 in)	28.04 in	+0.03%
285/40R19	Minus 2 (19 in)	27.98 in	−0.18%
225/50R19	Minus 2 (19 in)	27.86 in	−0.60%
235/50R19	Minus 2 (19 in)	28.25 in	+0.80%
255/40R20	Minus 1 (20 in)	28.03 in	+0.01%
295/35R20	Minus 1 (20 in)	28.13 in	+0.37%
285/35R20	Minus 1 (20 in)	27.85 in	−0.62%
235/45R20	Minus 1 (20 in)	28.33 in	+1.07%
285/30R22	Plus 1 (22 in)	28.73 in	+2.51%

Vehicles approved with 255/35R21 tires

Models whose Swiss type approval lists 255/35R21 as a standard or optional size (849 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 255/35R21 size

255 — section width in millimetres (10.04 in).
35 — aspect ratio: the sidewall is 35 % of the width, 89.3 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.