did a 50 miler today and it was the first time i'd needed to use the triple on my roadbike as i went up some big-momma hills. During the ride the chain fell off three times, first when i was just starting off at some traffic lights (middle front, middle back gears). The other two were changing down to the small front granny gear. The first was not serious as i hadn't clipped in, the second two left me rolling backwards down the steep hill and i had to throw myself over (still clipped in of course) on to the verge.

I've always suspected the chain has been too slack, when stopping pedalling it will hit the frame, however the bike was new from my LBS just two months ago. I recently had re setup all the derailleurs too in accordance with the parktool website.

Anyone think i should shorten the chain, or just change the derailleur settings? It's an ultegra triple with 105 front derailleur, 9 speed on the back with ultegra rear derailleur.