I have a 2006 Colnago C50 with Shimano DA front and rear derailleurs. I am running 12 - 25 cassette and a FSA 50 / 36 crankset. On the road and on the work stand the front shifts perfectly between both chain rings. on a fluid trainer and rollers I cannot shift from 36 chain ring to 50 chain ring. Can anyone out there explain why? Thanks.