Freerojo

Question: I want to replace the rear cassette from a 8 speed 11-28 to a 9 speed 11-32. At the same time I am removing the bar end shifters and dia compe brakes levers with a 9 speed set of 105 (5500 series) brifters that I have. I know the XT M739 SGS derailleur can handle the 32 cog, however I will end up exceeding the 38 capacity by 3. Is this workable? Will it cause shifting issues?

sch

No, the combo will work very well. Shimano is very conservative in their coverage ratings.

Unca_Sam

Exceed recommendations at your own risk. The downside is that attempting a large/ large combination (cross chain) can destroy the derailleur.

Unca_Sam

I'm surprised the capacity is only 38 teeth for a sgs cage derailleur! A step up isn't too expensive, I hope. There are contemporary Deore and XT derailleurs with adequate capacity, starting around $35 and maxing out under $80. You could always check on Ebay for used too.

Someone might chime in about road shifters and a mtb cassette. At some point the two lines diverged enough that the two no longer work together. I count know if it's starting with 9 speed or 10 speed.

Bill Kapaun

If you size the chain BIG:BIG, you'll have noticeable sag on small:small.
Since you shouldn't be using that combo, you can get by. Just a loss of "style points".

Slightspeed

If you do have a problem exceeding derailleur capacity there is a Wolf Tooth Roadlink adapter which drops the derailleur about an inch, providing a better passage of the chain between big gear and upper jockey wheel. When I put a 30t on my Roubaix, it had some chatter as the chain passed between big gear and jockey. Sometimes a 'B' screw adjustment will fix it. Wolf Tooth includes a longer 'B' screw if you need it. There are cheaper knockoffs on Ebay, but for $20, it's much smoother and quieter now. You might need more chain, but if you change cassettes, a new chain is usually in order. This bike is very happy running big big with a 50t chainring.

Wolf Tooth Roadlink is the black thing on the right between frame dropout and derailleur mounting screw. 5 minutes to install. This is a 105 long cage with a 30/39/50 105 triple crank.

shelbyfv

I agree. I've used similar combos numerous times. 9 speed mtn and road are all compatible.

Eggman84

You are correct that the RD-M739 total capacity is 38T. As others noted, you can probably exceed this to some extent. If your concerned about the total capacity, you can "upgrade" to the RD-M751, M761, M771, or still in production M772, all 9 speed MTB RDs that have a 45T total capacity for the SGS versions. When Shimano;s MTB groups went to 10 speed, they changed the cable pull so you can't use road brifters wth 10 speed MTB RDs, You say your putting on some 9 speed 105 brifters; you are aware the cable pull of Shimano's road and MTB FDs are different and the 105 brifter wont shift a MTB FD correctly.

Unca_Sam

You contradict yourself there.
Did the cable pull change at 9 or 10 speeds? Will a 9 speed 105 sti lever shift on a 9 speed mountain cassette or not?

Unca_Sam

I've sized that no problem. Calvin Jones has a video that explains it all clearly.

Unca_Sam

Given that the OP derailleur is a long cage, why does it have a lower max capacity? I saw somewhere that long cages are generally 80mm for shimano, was it different prior?

Freerojo

No, didn’t realize the pull ratio was different for FD. I might have a Tiagra Triple FD on hand though. Thank you

HillRider

Only if you aren't knowledgable enough to make the chain long enough to allow big-big. Then all you sacrifice is small-small and that's not a damaging combination if you use it inadvertently.

Eggman84

Please read carefully. Cable pull changed starting with 10 speed MTB RD (REAR derailleur) so the road brifters are no longer compatible with MTB RDs. The road brifters have NEVER shifted a MTB FD (FRONT derailleur) properly; the arm that the shift cable attaches to are different lengths so the cage of the road FD travels a different distance than a MTB FD. No contradiction, just keeping up with tech - thanks Shimano.

Eggman84

That may be a problem. The 3x10 speed Tiagra FD-4703 (as I think all Shimano road triple FDs) is designed for a 45 mm chainline. If you are running a MTB crankset, the chainline is likely 47.5 or 50 mm. So the Tiagra shifter cage may not swing out far enough to shift reliably to the large chainring, or may rub in the large ring small cog configuration. I have seen one "hack" to use a MTB FD with road brifters. I've not tried it but it is at https://forums.mtbr.com/shimano/succ...rs-933644.html.

You may have to copy the link and put it into your web browser, never sure if my links work.

Freerojo

As it stands it sounds Like I can probably get away with the XT M739 SGS in back with the 105 shifter. Now the issue is whether a Tiagra triple can handle the chain line.

The bike in question is a 1996 Cannondale RT2000 tandem Tandem Magazine Onine, Roadtest Cannondale RT 2000 right now it has Sugino Fuse 500 cranks with 54-42-32 chainrings. The link has some spec info.

Part of my reasoning with putting on the Brifters was to upgrade the mediocre Canti brakes with Tektro 926AL which matches the pull ratio of the 9 Speed 105 brifters.

I appreciate all the comments so far!

Freerojo

Here is a possible solution for using my 9 speed 105 brifters with LX mountain front derailleur. Anyone use this? Shiftmate 7: Jtek Engineering United Kindom

Darth Lefty 

This is why touring bikes come with barcons (or, one reason)

Unca_Sam

Another solution for you, potentially expensive and you should need the parts. Audax levers by Genevalle. Bring your own barcon or dt shifter and bolt it on, because I can't find a concurrent friction left shifter.

I only looked at them because I'm considering a drop bar for my rigid mtb/ adventure bike, and i could avoid barcons that way.

shelbyfv

Do you have any indication that crank has a mtb chainline? It looks like a regular road crank. Personally, if it was my tandem I'd keep the bar ends and get V brake drop bar levers (or the long pull Gevenalle) and go with full size V brakes. Tandems need serious stopping.

Eggman84

All may not be lost. From what I see on the internet, the Sugino Fuse 500 crankset uses a square taper bottom bracket. So you might be able to put in a shorter bottom braket if the chainline was a little wide for the FD you want to use, though you still need space for the small chainring to clear the chainstay. Another thing in your favor is that the downtube for Cannondale frames is "oversized" and this locates the FD outboard more than "standad" tubing. So my recommendation is to put on your 105 brifters, and see if it works. If it doesn't, you could post a new question here listing specific driver train parts your using and exactly whats not working. Best of luck.