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Shimano 105 double to compact

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Shimano 105 double to compact

Old 07-16-09, 04:24 PM
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eavonius
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Shimano 105 double to compact

Hello,

I've got a 2008 Cannondale Six13 with a Shimano 105 SM-FC5600 bottom bracket, into which a Shimano 105 crank with 53/39 cranks are installed. My rear cassette is 13/27. The front derailleur is a Dura Ace.

If I wanted to go compact (50/34), would I just need to buy new chainrings and a new chain basically? One other question if I go compact would it make sense to switch the back to 12/25 for smoother shifting or is 13/27 going to work fine too?

Thanks in advance for any advice or info.
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Old 07-16-09, 04:39 PM
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You won't be able to replace the 39 inner ring with anything smaller than a 38. Compact cranksets have a bolt-circle-diameter, BCD, of 110 mm. Your 105 has a BCD of 130 mm. If you choose to buy a compact crankset be sure you get the compatible bottom bracket with it. You should be able to run any Shimano compatible road cassette with the compact. It must have the same number of cogs (9-speed, 10-speed?) as your existing cassette. Is your cassette a custom? I thought the x-27 was a 12-27.

Al
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Old 07-16-09, 05:59 PM
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+1 on new crankset. The 13-27 will be fine (my wife is running a compact with a 12-27 and it shifts smoothly and gives her a bit lower gearing).
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Old 07-16-09, 08:09 PM
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Thanks, I will get the new crank and BB instead I guess. I thought I read somewhere something about needing a different front dereilleur as well. No?
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Old 07-17-09, 02:58 PM
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You'll need to lower the FD a bit but as long as you stay with a double it wil work fine.
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Old 07-17-09, 03:07 PM
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One more quick question - my cogset is 10 speed Shimano. Can I use an FSA or Campy compact crank or does it have to be Shimano? Thanks again.
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Old 07-17-09, 09:10 PM
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Originally Posted by eavonius View Post
One more quick question - my cogset is 10 speed Shimano. Can I use an FSA or Campy compact crank or does it have to be Shimano? Thanks again.
Does not have to be Shimano but shifting may not be as good as Shimano.
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Old 07-17-09, 09:35 PM
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Originally Posted by eavonius View Post
Thanks, I will get the new crank and BB instead I guess.
If you presently have a FC-5600 with it's matching outboard bottom bracket, then you can install a FC-5650 without changing the OBB. Both cranksets use the same OBB.
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Old 07-17-09, 10:06 PM
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Originally Posted by eavonius View Post
One more quick question - my cogset is 10 speed Shimano. Can I use an FSA or Campy compact crank or does it have to be Shimano? Thanks again.
I'm using FSA compact with shimano 10 speed. Works nicely.
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Old 07-20-09, 10:16 AM
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Originally Posted by laura* View Post
If you presently have a FC-5600 with it's matching outboard bottom bracket, then you can install a FC-5650 without changing the OBB. Both cranksets use the same OBB.
In the original post I specified SM-FC5600 as my bottom bracket. Is this considered the "matching bottom bracket" that will work with both 105 double and compact cranksets? I guess I've never heard the term outboard bottom bracket - I thought I had to replace the entire bottom bracket to switch to compact. Is the "outboard" portion a separate component?
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Old 07-20-09, 10:24 AM
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Oh I'm sorry I think I get it now. I was looking at the Shimano site. I guess SM-FC5600 is the bottom bracket used by both the compact and standard cranksets, and the FC-5600 is the standard crank (with the SM-FC5600 bracket) and the FC-5650 is the compact crank (with same bottom bracket)? Cool, so I can just buy the cranks and a new chain basically?
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Old 07-20-09, 03:28 PM
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Just the crank needs changing. The chain should be fine, just maybe take a link or two out (if it's Shimano I believe you need a replacement pin - or did they do away with that ?, which was why I use SRAM chains). General rule of thumb for chain length on doubles. With the chain on the large ring and the largest cog, the R derailer should be at about a 45 degree forward angle (cage to the top pivot). Just check as well the reverse - smallest cog, smallest ring (note that both these combo's are not recommended), so that the derailer angle is flat and doesn't allow the chain to rub on the upper jockey pulley.

Also as a general note, the current crop of cranks have what was once the spindle of the bottom bracket, now as an integral part to the right crank arm. The bearings called Bearing Cups) now are external and thread into the frame bottom bracket shell. Park Tools has a great website with useful descriptions and how-to's. http://www.parktool.com/repair/bikemap.asp

I would also recommend doing a gear chart to determine what changes in t he move to compact as opposed to what you have now. Sheldon's site is the best - http://www.sheldonbrown.com/gears/

SB
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