255/30R20 tire size

A 255/30R20 tire is 26.02 inches (661.0 mm) tall, 10.04 in (255 mm) wide and fits a 20-inch wheel. In inch notation it is roughly a 26.0x10.0R20.

255/30R20 dimensions
Overall diameter	26.02 in	661.0 mm
Section width	10.04 in	255 mm
Sidewall height	3.01 in	76.5 mm
Circumference	81.76 in	2,077 mm
Revolutions	775.0 per mile	481.6 per km
Rim diameter	20 in	508.0 mm

Compare 255/30R20 with another size

Current size

New size

Speed in mphkm/h

Overall diameter difference

+0.68%

60 mph on the speedometer = 60.4 mph actual

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

Ground clearance: +2.3 mm (+0.09 in)
Revolutions: 775 → 770 per mile

255/30R20 225/35R20

Side-by-side dimensions

	Current	New	Difference	%
Diameter	26.02 in	26.20 in	+0.18 in	+0.68%
Diameter	661.0 mm	665.5 mm	+4.5 mm	+0.68%
Width	10.04 in	8.86 in	−1.18 in	−11.76%
Width	255.0 mm	225.0 mm	−30.0 mm	−11.76%
Sidewall	3.01 in	3.10 in	+0.09 in	+2.94%
Sidewall	76.5 mm	78.8 mm	+2.3 mm	+2.94%
Circumference	81.76 in	82.31 in	+0.56 in	+0.68%
Revs per mile	775.0	769.8	−5.2	−0.68%

Speedometer error

Speedometer shows	Actual speed	Difference
20 mph	20.1 mph	+0.1 mph
30 mph	30.2 mph	+0.2 mph
40 mph	40.3 mph	+0.3 mph
50 mph	50.3 mph	+0.3 mph
60 mph	60.4 mph	+0.4 mph
70 mph	70.5 mph	+0.5 mph
80 mph	80.5 mph	+0.5 mph

Alternative sizes on the same 20-inch wheel

Sizes in use within ±3 % of the overall diameter of 255/30R20:

Plus and minus sizes for 255/30R20

Size	Wheel	Diameter	Difference
255/40R18	Minus 2 (18 in)	26.03 in	+0.03%
225/45R18	Minus 2 (18 in)	25.97 in	−0.20%
295/35R18	Minus 2 (18 in)	26.13 in	+0.41%
285/35R18	Minus 2 (18 in)	25.85 in	−0.65%
255/35R19	Minus 1 (19 in)	26.03 in	+0.02%
295/30R19	Minus 1 (19 in)	25.97 in	−0.21%
225/40R19	Minus 1 (19 in)	26.09 in	+0.24%
305/30R19	Minus 1 (19 in)	26.20 in	+0.70%

Vehicles approved with 255/30R20 tires

Models whose Swiss type approval lists 255/30R20 as a standard or optional size (3,455 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 20-inch sizes

Reading the 255/30R20 size

255 — section width in millimetres (10.04 in).
30 — aspect ratio: the sidewall is 30 % of the width, 76.5 mm.
R — radial construction (ZR on the sidewall means a high-speed rated radial; the dimensions are the same).
20 — fits a 20-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.