I just installed my newly bought 275-40-20 today. It marks the very first time in my life I'm trying this size on a Touareg. Quite a big difference over the stock 18's! More so than I had expected in all given aspects of the driving experience. I'll need some more time with them, but first impressions were that comfort mode on the air suspension felt like what sport mode did on the 18's, as far as ride compliancy over bumps. Handling and steering responsiveness on the 275-40-20's is a HUGE difference however! Very safe on the highway indeed, should a severe emergency maneuver ever manifest itself. The latter is what may keep me a 40 series fan for good. What might push me away from the 40's, and want to try the 45's next time, will be the slight increase road noise transmitted through the cabin, and harsher ride over our Montreal regions pot holes. How well this all adds up over time and weighed on the scale will be key. It's all user end preference at the end of the day.
I forgot to do this, but it would be cool for someone to record the dB level using a dB measuring apparatus (think iPhone APPS), with the 18's and 20's. Shame I completely forgot
Maybe next fall.