Hot answers tagged shimano
Yes, and Yes. Brifters will work fine and the cassettes will work fine. You can use any 9 speed Shimano road components in the drivetrain (crankset+chainrings with appropriate bb, chain, cassette, derailleurs) and the rear derailleur can be a <10 speed mountain derailleur as well. The chain can be made by KMC/SRAM/Shimano/etc. and the cassette can be ...
It is possible -- you can either find a 36 spoke internal gear hub (since you have a 36 hole rim) and have the wheel re-built with the new hub and bodge on the cables for the IGH shifting. Alternatively, there are automatic shifting hubs (e.g. the SRAM Automatix) which will also have a coaster brake and no shift cables. That being said, its probably going to ...
If you want to go from Shimano 10 speed road to 11 speed road, you'll need a new cassette, new shifters, a new chain and a new rear derailleur, since the cable pull ratios have changed (again). Zinn also notes that 10 speed FD might not shift as nicely as 10 speed FD with the 11 speed shifters, so may as well throw one of those in. So, in the drive train, ...
You should just be able to replace the chainrings for 11 spd ones. You can also get 9-spd 105 shifters if you just want tidier cable routing (I assume you mean internal as in under the bar tape) which would let you keep the rest of your groupset as is.
To directly answer your question, yes, 9 speed Ultegra is fully compatible with 9 speed Sora. Since even Sora is shifting to 10 speed, though, it might be time to consider upgrading the entire group set to 10 or 11 speed, if only for future parts availability.
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