105 Standard to Double Crank with Long Cage Rear Derailleur?
I bought a used bike that has 105 shifters and crank (53-39) and an 8 speed (11-30) cassette with an Deore XT rear derailleur. For a variety of reasons, I would like to have some lower gearing by swaping out my 53-39 crank for a double, either a Shimano 6750 (50,34) or Sugino 48,30. Will this work with my existing shifters and rear derailleur?
Pretty much anything will work with a long cage rear derailleur as far as max tooth count is concerned. You should be fine.
Metalheart, just a quick terminology issue... all of the cranks you describe are "doubles". The 53/39 is usually called a standard double. The 6750 would be called a compact double. The Sugino I think is termed a super-compact double (I may be wrong about that one).
Now on to your question. I don't see any issue with putting a compact on your bike right now. I don't have any experience with the Sugino crankset, so I won't speak to that working properly, but the Ultegra compact will work fine with your shimano double compatible derailleur. The only 2 mods you'll have to do will be to move the front derailleur down so it sits properly in relation to the chainrings and shorten your chain because your largest chainring now has less teeth.
Now the Sugino may work fine, or it may not. I only hesitate because I don't have direct experience with it and it has an 18T difference between chainrings. This is a large jump to me. But I'm sure somebody with more knowledge than myself will come in shortly and offer assistance.
Edit: I misread your post as looking for fd advice. Feel free to ignore my post as I didn't address the rd.
Thanks for the above responses ... still have not made a decision about the crankset. Can I use any Shimano 105 or Ultegra crankset (e.g., 5650, 5750,6750,etc...)? It also seems I may be able to use something like the Sugino 48/34 or the Velo Orange 48/34? It is not clear to me what characteristics of the crankset determine compatibility with other drivetrain parts?
If you use a relatively wide chain with a crankset designed for a narrow one, you may have considerably more chain rub against the face of the big ring, particularly if the size differential between the rings is high (e.g. compact combos). I bring this up since you've got an 8-speed system now.
Originally Posted by metalheart44
Also, your 105 FD may not be able to accomodate really large differences in chainring size without the chain dragging in the tail in some combos.
5 shim washers,1 around each chainring bolt will give you space between chainrings.
any 110 bcd crank can be fitted with 34 and whatever big ring you choose..
just time the upshift for the crest of the hill, take force off the pedals, and thus the chain.