triple to compact double.....what do i need?
 

I posted this in the "road" forum, decided to bring it here.......here goes:

i have a triple crank right now (52/42/30) with a 9-cog rear cassette (12-25). all came stock, full 105 components on my specialized allez (2001). i want to get a compact double (close to 50/36). can i just get it and slap it on (with some FD adjustments) or will i need to overhaul the whole drivetrain? new FD? new shifters? just trying to get a feel for the right way to go about this.....thanks!

ps-after a couple replys in the road forum, my answer to the "why?" question is because i never use the highest and lowest gears that i would be losing, and the weight savings (i know, minimal) and the convenience is worth it. plus i just want it. :D

to go 3 > 2 these are the problems

1.) you will need to shorten the B/B to a 109 or if you are running the 110 will work. But not the 113mm.

The frt derailleur on a triple has a longer inside plate. Looking at the drop above listed, there is normally a 26t diff. Which you should be a go on this one.

as thepest has said, a new bb might be needed, but to really take advantage of the compact, you might want a short arm derailluer. a short arm and less chain should result in quicker shifting.

You can get by with a new R crank with the desired CW and a shorter BB. Problem is Shimano is very proud of their compact cranks and wants $250 or so for it (no BB IIRC). FSA sells the Gossamer compact but you would need an ISIS BB. FSA also has carbon compact which weighs 3-4oz less than the Gossamer for triple the money (weight reduction at $50/0z), also ISIS. The der you have will work ok according to most converters that have posted in the past, but a shorter cage RD would be a little snappier. If your frame has a FD mount 'brazed' you might have a problem with the der height above the CW.
Steve

What works, what doesn't
 

The front der will work, but not too well.
The rear der will work, but not too well either.
The bottom bracket will not work too well because the chainline is too far offset.
The crank is obvious, at least I hope you can figure it out.
The brifters are a go.

IMO, you should sell the old 105 group, seeing as most parts will work marginally at best. If you had a double, you might be able to get away with just a crank change at best. At worst, you would have to swap out the the front der and crank. Good luck and let us know what happens.

Tim

Ritchey makes a very nice compact crank for about $125-150. Also uses the octalink bottom bracket system. All advise fro cs1 is +1 from me.