I am too lazy to look up the actual part numbers but the compenents were new four summers ago when we bought our tandem with all Ultergra Brifters, FD and RD and 52-39-30 chainrings and 12-27 cassette and Davinci cranks. 10 spd, superb shifting front and rear and no shiftmate to tweak. I asked our builder about the IRD cassette because so many tandems were being sold with them and I thought that might be the way to go but he talked me out of it. He said that they had tested them and he did not like the way the shifted. As we found out later, a number of people reported having trouble with them. At that time he said if we wanted a bigger cog in the back we should go with the XTR RD and 9 speed cassette and actually set the bike up that way originally but I asked him to swap out and use the 12-27 and Ultegra RD. No regrets to this point but as the years go by we may need a bigger cog back there.