Weird thing about my new Pirelli Angel GTs. I got 190-55-17 for the rear, not A spec as they weren't available. If I get 9k out of the set, I'll be doing backflips, I got 4600 out of stock BT-021's. But on a 700 mile weekend trip (Rockerbox in Milwaukee and Wisconsin MotoGuzzi rally
http://www.flickr.com/photos/cpsmith58/sets/72157634937447740/) that was about 85% backroads and at a fun pace and also fully loaded, I was initially chasing the front end all over the place and running wide, it was scaring me a bit. Bear in mind, I have at least 500 miles on this new set and haven't noticed the issue. Perhaps I hadn't noticed but I lean a lot and hammer it out of corners on a daily basis, thats why I bought it (see above tire wear on stock tires).
So despite the fact I had a lot of extra weight on (dry bag FULL of old heavy sleeping bag and tent, bag lawn chair etc, both side bags full to the brim, no top trunk and no tank bag, me 200 lbs nekkid but fully geared), I BACKED way off the rear preload (maybe 5 or 6 clicks, I should have counted but didn't) and the bike transformed, I rode the wheels off it hard and had a blast, no problems whatsoever.
I do know that normally, when you add a ton of weight to the rear (passenger etc), you ADD preload, but I took it off and it made the bike back into the same trustworthy ready to rock beast it had been before. I don't really have an explanation. All I know is that I was able to enjoy my trip! So fun riding a handling and HP overdog. 2 friends had BMW boxer twins, one on an HD bagger, no problems keeping up, cough, cough.