Audi fitment catches people out more than any other make, because the bolt pattern is the same across the range but the hub is not. Two Audis can share 5x112 and still need different wheels.
The two platforms
The small platform covers the A3, S3, RS3, TT, Q2 and runs a 57.1 mm hub. It shares this with the VW Golf, Skoda Octavia and SEAT Leon.
The larger platform covers the A4, A5, A6, A7, A8, Q3, Q5 and the RS models, and runs a 66.5 mm hub.
Both are 5x112. A wheel will physically bolt to either. But an A4 wheel on an A3 leaves a 9.4 mm gap around the hub, and that gap has to be filled.
The exception
The Q7 is different again: 5x130 with a 71.6 mm bore, shared with the Porsche Cayenne rather than the rest of the Audi range. Older cars before roughly 2004 used 5x100.
What this means when buying
If you have an A3, S3, TT or Q2 and the wheel lists a 66.5 or 66.6 mm bore, you need 57.1 mm spigot rings. This is extremely common, because most aftermarket wheels are bored for the larger platform.
If you have an A4 or above and the wheel is 66.5 mm, it is hub centric and needs nothing.
Sizes by model
A3 and S3 suit 18 or 19 inch, typically 8 or 8.5 inches wide. RS3 handles 19 inch comfortably.
A4 and A5 work well at 19 inch, 8.5 inches wide. A6, A7 and RS6 carry 20 and 21 inch without looking overdone, and the RS models often ran staggered from the factory.
Q5 and Q7 take 20 to 22 inch, though load rating matters more on the heavier SUVs.
Checking yours
The quickest way is the hub itself: measure the raised lip the wheel sits on. Or send us your registration and we will confirm the bore, the offset range that suits, and whether rings are needed.