Campy derailleur ?

[sokyroadie]

48/34 - 13/29 - short cage RD will it work? I would only use the 29 with the 34.

I also think there was a thread on which clamp on Campy FD's can be converted to braze on, but I can't find it. Anyone remember it?

Thanks,
Jeff

[thwart]

I now have 2 bikes (one compact crank, 50/34, and one with a standard crank) with short cage Campy RD's and 13-29 cassettes. Must say I only tried this after hearing from a couple of other Forumites who found this actually worked OK, contrary to well-established Campy doctrine...

They both work very well, even when their lamebrain rider occasionally shifts into the big/big combinations (which I obviously try to avoid).

Compared to a couple of other bikes I own which are set up similarly, but with medium cage RD's, the shifting is indeed a bit more crisp with the short cage RD's. As one would expect, I guess. FWIW, one RD is Centaur, the other Record, and all bikes referred to here are 10 spd, running Campy UN chains.

Are there any long-term issues here? Durability of the RD or cassette? Who knows... but I doubt it.

[Dave]

The answer to this is it wil certainly work if you never shift to the 48/29 and might work with this combo, if the chainstay length on your frame if perfect and the chain length is set to the maximum.

Set the chain length to the longest possible in the 34/13, with the chain routed through the RD in the normal fashion. As long as the chain causes the lower RD pulley to swing down slightly when the ends are brought together and does not rub on the upper chain guide tab, it is not too long.

What some people don't realize is that some frames can gain up to 2T of wrap by having the perfect chainstay length.


All this said, a medium cage would be a better choice and will shift just as well. The only difference with a medium cage RD is the cage length. The extra length does not slow the shifting. It merely provides more wrap capacity.

[thwart]

Just as an addendum here, given Dave's post:

Both bikes have 'normal' 41 cm chainstays.

The chains lengths on both bikes were originally optimally set for 12/25 cassettes, and not altered when the 12/25's were changed out for the wider geared 13-29's.

That's actually the reason for running these 'you can't do that' set-ups---I really didn't want to break open the low-mile UN chain, which would have been necessary to swap out a short cage RD for a mid-length cage model.

And for some of the hilly rides my knees said please, please give me a 29! :rolleyes:

[Dave]

One common misconception is that chain length always changes with the RD cage length. I've used the same 53 inch chain on my bikes, with a 53/39, 53/39/28 and 50/34 using either medium cage (for the triple) or short cage RDs and 11-25 or 12-25 cassettes.

The only time I increased the chain length to 54 inches was when I used a 53/39/28 with a long cage RD and a 13-29.

You can swap RDs without breaking the chain, but you have to take the RD cage apart.

[sokyroadie]

The bike this is going on has 45cm chainstays is this better or worse? The reason I am questioning this is that I have a partial silver Campy group with a short cage RD that I was going to use for this cross bike build. I also have a complete Centaur Gray build on another bike with both short and medium RD's that I can switch over - it's just more work.

Thanks for the reply's.

Jeff

[Ken Robb]

I have bikes with chainstays from 40-45.5cm. They all shift fine but the bikes w/ longer ones make less noise when running at the extremes of the cassettes.

[Dave]

The chainstay length that produces the maximum wrap capacity will vary depending on the exact size of the big ring and largest cog, so a given chainstay length might be perfect for one setup and not as perfect for another.

Park tool has what they call the "rigorous equation" on their website, but I find that it does produce the correct answer. Plugging in the numbers from my bike, it suggests a chain length of 52 inches, with a 50/34 and 11-25 cassette with 16 inch chainstays. In practice, a 53 inch length is what I use and it is not too long. I have chain tension in the 34/11.

What you are looking for is a chainstay length that produces a suggested chain length that ends in a whole number. A suggested length that includes a half inch, like 52.5 is the worst case, since you can only make the chain 52 or 53 inches long.

http://www.parktool.com/repair/readhowto.asp?id=26

I've seen some on-line length calculators, but most don't tell you what equation they use and only display rounded off numbers, so I don't trust those.