I'll be working on my dad's bike this weekend and we have an issue we have is the Campy Super Record rear derailleur. He just switched 50-36 compact crank in the front. The shop took a link out of the chain but when you shift into the 36 ring and move progressively higher (smaller rings) in the rear the derailleur isn't taking up enough slack so the chain ends up drooping and resting on the chain stay.

In the large ring the chain is about right but you can't shift into the big/big combo.

Ideas? We're going to try and swap in a Simplex SX630 long cage derailleur tomorrow and see if that helps.

Yes - photos to follow tomorrow.

Options:
1. get a long cage derailleur.
2. don't shift to the small/small gears.
3. shorten the chain and don't shift to large/large gears.

I disagree with 3. My best practices include always leaving the chain long enough to accommodate big/big. This is like installing a big red self destruct button on your bike. Just like a self destruct button, gou may never intend to use this combination, but just a moments inattention/forgetfulness can have bad consequences, just like accidentally leaning on the self destruct button.

There are lots better solutions, starting with leaving the chain longer and avoiding the small small combo.

The problem actually starts two rings before the small small. We'll try the long cage tomorrow and see if that works.

I put a 38 - 52 combo on my super record equiped bike for a trip to the mountains and had to avoid all small - small and big big combo's.

The long cage replacment should fix this on your bike but make sure you do not chuck the old derailleur out!

Nope, the old derailleur is staying with me. He gets my Simplex SX630.

I disagree with #3. Shortening the chain to the point you can't use big/big, is like taking your car and at 60MPH shifting it into reverse it's a good way of leaving pieces of transmission (in either case) all over the road.

The shop that put on the crank though, may not have shortened the chain enough. Essentially when sizing a chain, you want it to just fit the big/big combination, there are probably 65,536 pages on the Internet on determining chain length, google is your friend. What I do is feed the chain through the RD and FD, with them shifted to the big/big, pull it as tight as possible and cut the chain at the next full link, if you do end up in that combination, the drive train will not self destruct.

With the chain just able to fit big/big, if there is slack at the small/small you need a longer dérailleur on the back. Although neither big/big or small/small should ever be used, nearly every rider at some point will end up in either one. What I do, is take a small container, a 35mm film can is really good for this, and put the extra links that I take off in there, then if I damage a chain, I have those extra links to repair it. Say you bust a link, you take out the damaged links and replace them with the spare ones from that chain, your back in business. BTW if you do bust a chain, it's probably time to review your bicycle maintenance procedures, as properly maintained chains rarely break.

i disagree with people disagreeing with my #3 this is the c&v not the commuting forum after all.

obviously the best solution is to get a proper derailleur to take up the slack, but it isn't the only solution. if the guy really loves riding in small/small, he can just shorten the chain and know to never go up to big/big. he could ride the bike for 30 years and never blow the RD. i think people probably ride in small/small a lot more than big/big (i don't think i've ever run big/big).

I have a bike set up so that it is next to impossible to get the shift to big-big. Not really a problem, as the bike tells you long before you can garner the strength to shift to the impossible combination.

A racing bike should never be set up that way, because people in serious oxygen debt do strange things.