Greetings. What would be the largest wheels and tires that will work on a 2006 A6 (C6) Avant Quattro?  Are there any adverse effects from increased wheel and tires from Original Manufacture's Equipment?   Thank you.

Hello Stephan,

Thanks for being in touch. 
Obviously the larger the wheels, the lower the tyre profile ( height) must be, to retain the same outside diameter of wheel plus tyre. You also trade off a harsher ride by increasing the wheel diameter. 
Best answer to your question is to look in the correct owner’s handbook for the car, and see what wheel and tyre sizes are listed there as alternatives (under tyre pressures would be a good place to start). 
If you stick with the manufacturer’s specified alternative wheels and tyre sizes, then you should not have any issues with insurance implications.

Kind regards,

Gareth. 

Hi.

If you have any issues with insurance at all then please feel free to drop me a line.

Regards,

Dan.