I have a 10-speed 2013 Specialized Allez Elite with Tiagra componentry (and an 11/28 105 cassette) and would like to install my old Shimano 105 rear derailleur in the back to replace the Tiagra one. The 105 rear derailleur came off a 2015 Roubaix which was all-105.
Will this work? I assume the Tiagra shifters' different pull ratios will simply result in the rear derailleur being pulled at... a different ratio. Will this setup run cleanly and shift smoothly? Are the chain widths slightly different between 10 and 11-speed as well? Is this destined to fail?