Drtumolo

I am building my first road tandem. I am using ultegra 9spd brifters. what would be the best rear derailleur to use with them?

Roger M 

Shimano made an Ultegra 6500 series long cage rear derailleur. That would be the match for your STI levers. I would think that a 9 speed XT or LX, 105, or Dura Ace(maybe even XTR) part would shift fine with those shifters.

As long as it is a 9 speed derailleur.

Drtumolo

I know I want a mountainbike derailler so I can use a 11-34 rear. Just not sure what mtn derailler would be best.

Goldrush

Our tandem has Ultegra 9 speed shifters. I use a Shimano XTR mountain bike derailleur with a SRAM 11-34 cassette. This has worked well over several thousand miles.

waynesulak

We have used XTRs and had good success. Any 8-9 or 10 speed traditional Shimano RD should work fine. I don't know about the newer Shadow RDs. Anyone know about them?

Drtumolo

Thanks for the info. I was wondering about the shadow tech ones also.

Shimagnolo

The Shadows are fine. Just make sure you get the 9s version, and not a 10s, (which has a different cable pull rate).
They also let you go up to a 36T cog.

cajoe

The Shimano LX M581 is a pretty good deal and works great. We're running one with Ultegra 9sp brifters on our tandem. I see Jensen USA still has them in stock.

DubT

It all depends on your gearing, you have not provided enough information. What size rear cassette are you using and what chain rings. The rear dérailleur has to have the capacity to handle the gearing you are using.

Wayne

Drtumolo

What is the advantage of the shadow tech derailleurs?

Shimagnolo

As opposed to other RD's where the mounting bolt and the pivot point are one and the same, the Shadow moves the pivot about an inch toward the rear of the bike. I think this is what helps it handle larger cogs. Shimano's marketing blurbs make a fuss about the RD being closer to the wheel so it is better protected from damage, but that is irrelevant IMO.