SRAM Road front braze-on derailleur: spec not compatible with industry standard

[e.Gellie]

I've just finished dremelling a SRAM Rival braze-on front derailleur to ensure it will complete a downshift properly when mounted to a conventional braze-on mount~!

I jumped on the phone to Dazza at Llewellyn Bicycles here in OZ and confirmed the dimensions of 2 older mounts he had on hand. The Sachs design front derailleur braze-on mount we both use is the same in this respect to those older parts, so that would probably be an Industry Standard ....... (?!)

So my setup is on an oversized, 31.8mm seatube fitted with a conventional braze-on mount (in this case a Richard Sachs part); the mount hole is 28mm from the centreline, and I'd calculate the dimension is 26.5mm on a 28.6mm seat-tube. Both of which will exceed the SRAM spec of 25mm. This same derailleur in clamp-on form is made in both 31.8 AND 34.9mm versions!

I'm posting this info here because think we all need to be aware ... and I'm not impressed....... the dremel work 'seems' to have increased the down-shift swing enough....

The SRAM spec is on page 8 of the PDF "Road and MTB Components" (a big (3.3Meg) on this page
SRAM | Service | New Technical Specifications
and below is the particular section of that document
SRAM TechSpecs MY08 page8.JPG

[Clockwork]

What about a thin spacer betwixt the BB and BB shell?

[e.Gellie]

What about a thin spacer betwixt the BB and BB shell?

I have here a Rival crank with external bearings .... so no spacers there (unlike the MTB setup) ... I don't think there's room for spacers (?).

I needed another 2-3mm, and removal of 1.5mm of material did the trick.

[e-RICHIE]

i just built up nahbs show bicycles with model year red and force (braze on red and clamp on force) and all works
well. which dimension precludes you from having the part do what? (sorry for that sentence structure atmo).

[zank]

Yeah, but Richie, you are using 28.6 mm seat tubes. Ewen is using a 31.8 and it's pushing the derailleur too far away from the centerline of the frame. My advice is to use clamp-on derailleurs for any size seat tube other than 28.6. I know that doesn't help you at this point though, Ewen.

[Dornbox]

Perfect timing with this topic! I'm getting ready to build myself a bike with an oversized seat tube (first time) in the next month or so. Although I was also thinking about using a clamp on as well... incase I ever wanted to run the frame as a 1X10 or single speed. Regardless, I wouldn't have even thought about something like this until I was building the frame set up; and at some point I would have built one with a braze on derailleur. Damn I love the Salon! Thanks Guys! -Chris

[johncaletti]

So, I think this is what Zank was referring to, but said another way, I read it as the braze-on FD mounts are designed for a 28.6 seat tube. If used with a 31.8 ST the der mounts 1.6mm further out, which may preclude the der from functioning properly/getting far enough in to shift into the small ring. Is there a source for braze-on mounts designed for 31.8 seat tubes?

[johncaletti]

By the way, SRAM seems to be disappointing a bit again here.
a) the rear der. doesn't like thinner (steel) dropouts/hangers
b) they don't make a 28.6 band clamp FD
c) the front der seems a bit tough in this instance. (I haven't tried Shimano or Campy with that setup, so maybe they aren't good in that situation either.)

I believe SRAM, Campy, and Shimano only make their Braze on FD> band clamp adapters in 31.8 and 35, not 28.6 - bummer.

[Dazza]

I have built XL Compact and Cadenzia frames for many years using 31.8 seat tubes
and using the Richards Sachs braze on deralleur boss.
So far I have only fitted Campagnolo and Shimano front derailleurs to this boss and there is never a problem.
The problem is the SRAM FD seems to have limited movement, so fitted to the braze on a 31.8 ST with all or some cranks there is some movement restrictions.

[e.Gellie]

It seems this particular SRAM derailleur is so close to it's limit of inward swing, that it's hit and miss whether it clears the chain in lowest gear. It seems it's down to small variations in the shape of the forging/casting of the outer link (at the spot in the pic below) for it to work on a 31.8 seat-tube (on the example I have here).

Effectively the SRAM braze-on derailleur is only intended for 28.6 seattubes judging by the spec, and apparently not enough allowance has been made for 31.8's, and I've come unstuck assuming it will work. (as Dazza has indicated the Shimano and Campag do). This may only be for the Rival part, given Richard's success with Red and Force. I also have Shimano and Campag equipped versions of this with no reports back.

... which dimension precludes you from having the part do what?

Richard, it's the 25mm dimension, and I'm not saying your part is wrong.

Campag specs? The Shimano spec seems to be 25mm, here
http://pvdwiki.com/images/4/4c/Requi...ailure-web.jpg

p.s. The braze-on is well aligned on this frame.
rivel der clr.jpg

[Dave Anderson]

Interesting. Like Dazza, I have built bikes with 31.7 seat tubes and E-Richie bosses and have had no shifting problems. However, I also have not tried a SRAM derailleur with the combo.

John, Problem Solvers sells a 28.6mm braze on clamp adapter. The newer ones are fairly nice looking....similar to shimano actually.

Dave

[ulrich vogel]

Is there a source for braze-on mounts designed for 31.8 seat tubes?

Yes there is one from Everest. Call Peter / ceeway. But the braze-on mount isn´t a nice one.

Ulrich

[Bssc]

Sram front der. spec is the same as Shimano/ Campy it has a shorter inward through there use to be a shim available to alleviate the problem on large diameter tubed bikes. ( OCLV's were notorious for the issue)

[jerk]

Yeah, but Richie, you are using 28.6 mm seat tubes. Ewen is using a 31.8 and it's pushing the derailleur too far away from the centerline of the frame. My advice is to use clamp-on derailleurs for any size seat tube other than 28.6. I know that doesn't help you at this point though, Ewen.

according to "spec" no frame braze-on fder should allow any fder to work on an oversize tube. campy and shimano just have more tolerance built in or else we would have figured this all out via phonecalls and post cards when cavemen were still building MAX frames.

[zank]

max rules.

[e-RICHIE]

kucf this atmo i cannot profit if clamp-ons are used atmo.
i have a braze-on part empire to build.
find a way or i'm goin' jersey on the industry.

[johncaletti]

Perhaps a new part is in order... version 2.0 for fat pipes.

[Tom Kellogg]

Two solutions: a) never use a BZ-on with seat tubes over 28.6 if you are going with SRAM. b) get SRAM to fix their design. That's all I got. (by the way, the old Campy triple FDs had the problem big time on anything over 31mm)

[e-RICHIE]

b) get SRAM to fix their design.

i am gonna work this route atmo. if you get mad enough, some folks react atmo. it happened with 28.6 clamps from campagnolo (up to a point) and also classic shaped 'bars
from 3T and oval concepts. these were dead and then they weren't. since i am a dedicated sram cat my plan is to go howard beale on this issue as soon as my plate is clear.

[hmbatrail]

I also sent an email to Ed over at SRAM under the logic that if they hear the complaint from multiple folks they will be more apt to do something about it.