clta6

I'm thinking about buying a 2012 A6 3.0T Prestige. The car has the 20" "Sport" package which as I understand it is 20" wheels + some modifications to the suspension. Does the modified suspension mean that I would not be able to replace the 20" wheels with the factory 18" wheels if I wanted to?

Glisse

No it doesn't prevent the use of 18" wheels fitted with the correct tyres (245/45R18), but if a comfortable ride is high on your list of attributes, surely better to buy an A6 without sports suspension?

clta6

Normally, I would agree with you whole heartedly regarding avoiding a vehicle with sport suspension.
Lightly-used A6's are somewhat hard to find in the US under the $28K price point. Especially with the Prestige package.

Its not so much the ride that is an issue for me....its more about the fact that the 20" wheels make me nervous on road trips....one decent pothole on the interstate here and you could easily pop a double flat. I use to own a M3 which had 19" wheels and low-profile tires and road trips were nerve racking (luckily I never had any tire issues, but I was always fretting about the possibilities...which is one reason why I sold it).

I know I can put all-season tires on the 20" rims instead of the summer tires...but I don't know that it would make road trips less nerve-racking....which is a shame because the A6 3.0T is a car to be enjoyed on the highway. I was thinking maybe going back to the stock 18" rims and "less low-profile" tires would maybe just ease my mind on the highway. Also, I would probably get rid of the run-flats (like I did on the M3) and buy a spare tire, which takes up trunk space...

Glisse

Understand, the 18" wheels make sense re. wheel damage, and if you are coming from an M3 with 19" run-flats, the sport suspension is not going to be an issue for you.

Audi do not commonly use run-flats on sedans / coupés / Sportbacks / Avants, and the C7 models used a space saver spare tyre. At least, mine did. Perhaps there were some differences in US spec cars.