My LBS put on a Tiagra 4550 Compact crank50/34 on my Cervelo Soloist SL -- I had a Dura Ace crank 53/39 with a 12/27 cassette. The problem I first experienced with the 4550 was that I could not get into the 27 cog without the chain jumping off the big chain ring. After many trips to different bike shops it works now but I dont know exactly why nor hasnt anyone told me why .
After looking through this forum I see that the 4550 is for a nine speed. It works now but what are your thoughts on this whole thing besides having a low level used crank on such a great bike.
Would appreciate your thoughts -- the smaller crank seems to work well for me , thinking of going for a new Ultegra compact.