2021 Audi A4 tire size

Most common factory size

P245/40R18

Tire sizes by trim

Source marks: one source

2021 Audi A4 tire size by trim
Size	Trims	Width, mm	Sidewall, % of width	Rim, in	Diameter, in	Sidewall, in	Revs per mile
P245/40R18	40 TFSI Premium Plus AWD, 40 TFSI Premium AWD, 40 TFSI Prestige AWD, S line 45 TFSI Premium Plus AWD, S line 45 TFSI Premium AWD, S line 45 TFSI Prestige AWD	245	40	18	25.72	3.86	784
P245/45R18	allroad Premium Plus AWD, allroad Premium AWD, allroad Prestige AWD	245	45	18	26.68	4.34	756

What P245/40R18 means
Part	Number	Meaning
Type	P	Passenger car tire.
Width	245 mm	Tread width. 9.6 in.
Sidewall	40	Sidewall height is 40% of the width.
Construction	R	Radial tire.
Rim	18 in	Fits 18 in wheels.

Within 3% of the stock diameter. A common shop guideline, not a maker spec.

Sizes within 3% of P245/40R18
Size	Rim, in	Diameter, in	Change	Speedo reads at 60 mph
285/30R19	19	25.73	+0.1%	60.0 mph
245/35R19	19	25.75	+0.1%	59.9 mph
245/45R17	17	25.68	-0.1%	60.1 mph
215/45R18	18	25.62	-0.4%	60.2 mph
275/35R18	18	25.58	-0.5%	60.3 mph
225/50R17	17	25.86	+0.6%	59.7 mph
205/55R17	17	25.88	+0.6%	59.6 mph
235/35R19	19	25.48	-0.9%	60.6 mph

Sizes within 3% of P245/45R18
Size	Rim, in	Diameter, in	Change	Speedo reads at 60 mph
195/50R19	19	26.68	-0.0%	60.0 mph
205/60R17	17	26.69	+0.0%	60.0 mph
275/40R18	18	26.66	-0.1%	60.0 mph
245/40R19	19	26.72	+0.1%	59.9 mph
245/50R17	17	26.65	-0.1%	60.1 mph
225/55R17	17	26.74	+0.2%	59.9 mph
275/35R19	19	26.58	-0.4%	60.2 mph
225/50R18	18	26.86	+0.7%	59.6 mph

Checked against 292 factory sizes listed for 2009-2027 US models.

Tire pressure is on the driver door sticker. Not in this data.

Optional wheel packages may differ.