Originally Posted by
rccardr
ALL Shimano road derailleurs and shifters are backward and forward compatible with the exception of DA 740X, from 6208 SIS through 7900 DA and everything in between. 7800 freehubs have a doifferent pattern than other freehubs, but that's a minor issue and has nothing to do with cog spacing or cable pull.
Most of the MTB stuff is also compatible with the road stuff; there are some exceptions, e.g. 10 speed MTB derailleurs.
So, yes, those 10 speed DT shifters will shift all the way across a 6-7-8-9-10 speed cassette if the system is properly installed and adjusted. It's possible that the Wolftooth link changes the geometry to the extent that it limits the total travel, but I'd be surprised.
Maybe if the lever is set to the friction mode... But the amount the der will travel PER "click" is specific to the cog count (and family of actuation ratio). So a 9 "click" (or 10 cogs that has 9 steps between the 10 cogs) lever will move a actuation ratio compatible rear der one cog per one click. But those same levers won't move the der enough for the wider cog spacing of a 5,6,7,8 or 9 cog cassette.
The first gen DA system was designed around a 1.6mm diameter cable and has it's own cable actuation ratio. Shimano changed both to when they introduced the 600 (Ultegra) series to indexing. Andy