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Changing cog set
Hi, I have a road bike with shimano 105 10 speed drivetrain. My cog set is 12-27. I would like to change my cog set to 11-32. I know this would be a MTB cog, probably the Shimano XT CS M771. Its a 10 speed with the 11-32 cog but learned it is the mountain bike equivalent of Ultegra. My question is, can I use my original 105 derailleur, chain, shifters, etc. for this change. I have had 2 suggestions from friends:
1) put the cog on and try using the rest of the original set up and see if the shifting is smooth....if not, get a medium cage Shimano Ultegra RD 6700 that they said will work with the 11-32 cog.
2) assume a complete change, buy a Sram 11-32 cog, a Shimano 9speed XT derailleur that works with a 10 speed and a new chain longer chain.

I don't want to give up the smooth working of the 105's so am reluctant to idea #2, mixing brands.
Thoughts anyone? can you help with some advice on this modification.
In general you can mix Shimano MTB and road products (with some exceptions). However:
- the rear dérailleur needs to have the correct capacity / specs for the cassette (get a MTB RD)
- the chain needs to be longer

Other than that I don't see any problems. The "speeds" on the RD are... well... not relevant. Any 8-10 spd should work on any 8-10spd system (at least with Shimano). The SRAM cassettes are fully compatible to Shimano, the rear dérailleurs are not. Mixing SRAM casettes or chains with Shimano drive trains is no problem and anecdotal evidence tells of people who replace the Shimano chain by SRAM to get better shifting performance.
Hi Joe, thanks for your reply.
Just to review so I understand:
1) no matter whether I use Sram/Shimano cassette, I have to change the rear derailleur
2) If purchase the Shimano XT CS M771 (MTB) cassette I will need to purchase any 8-10 speed Shimano MTB RD (any good recommendations?)
3) will need longer chain

Any experience with which of the cog sets is the best? Sram Apex is getting a lot of press lately, but I heard the Shimano XT CS M771 is equivalent to the Ultegra line so thought it would be a good match with my 105 current set up.

Again, thanks for your reply, I would really like to make this change soon.
1) yes, you need a longer cage
2) last years XT or the Ultegra you mentioned? I like staying around one level of components (not mixing DuraAce with Sora...)
3) yes, you need to replace the chain anyway, it is good practice to replace cassette and chain at the same time as they both wear similarly. You can get away with replacing a slightly worn chain and not changing the cassette (though the chain will probably wear a bit faster) but no the other way round (unless the chain was brand new).

In my opinion the SRAM Apex, while a nice thing, is a marketing ploy... (well, that sound a bit too strong, but I'll leave it that way, I'd totally buy a Randonneur with it, alas space, time and money don't permit that): Mixing Shimano's MTB stuff with the road stuff has been possible for a while... Choose the cassette that has the most sensible spacing for you. There are some that say shifting is nicer on SRAM cassettes and the system is also quieter, I don't know.

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