# direct/e-type front deraileur mounting ?



## sholmboe (Jul 25, 2008)

Anyone out there have any info/specs for mounting a front derailleur like this?

https://www.specialized.com/OA_MEDIA/2010/bikes/7303-11_l.jpg

Also, opinions? At first glance it seems to solve a lot of interference problems with the front derailleur and main pivot/drive side chain stays. Any disadvantages?

Thanks for any help...


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## Walt (Jan 23, 2004)

*That's the SRAM standard*

The Shimano standard is different, you can find it here:
https://www.pvdwiki.com/index.php?title=Shimano_Framebuilder_Info

The SRAM info is available in their XX tech docs, which I can't remember the link to, but is easy to locate with a search. If you can't find it, email me and I can send you the .pdf, I've got it somewhere on this rat's nest of a computer.

I have not done anything with the SRAM direct mount setup yet, but I am a big fan of the Shimano ones already - great shifting under load, very easy to fabricate and mount up, and inexpensive. Plus you can do unconventional seat tube configurations and the derailleur profile is nice for tire clearance.

It would be nice if they had adopted a single standard (sigh) so it will be interesting to see which one sticks around.

-Walt



sholmboe said:


> Anyone out there have any info/specs for mounting a front derailleur like this?
> 
> https://www.specialized.com/OA_MEDIA/2010/bikes/7303-11_l.jpg
> 
> ...


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## swift (Apr 3, 2007)

Actually, that's the Specialized interpretation. It uses an E-type derailer with the BB mounting ring removed from the derailer. Corsair uses it as well and maybe others I'm not familiar with. I've not used it (I'm strictly an IGH guy when it comes to geared mt. bikes) but have heard/read good things.

I agree; it would be nice if there were some common ground in the industry for this sort of thing.


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## sholmboe (Jul 25, 2008)

Here's what I've got so far...

The Shimano DMD's that mount via a mounting boss shown here...

https://www.pvdwiki.com/images/thumb/c/c9/Direct-mount-MTB-FD--web.jpg/606px-Direct-mount-MTB-FD--web.jpg

are for Shimano derailleurs of this type...

https://techdocs.shimano.com/media/techdocs/content/cycle/EV/bikecomponents/FD/EV-FD-M771-D-2859_v1_m56577569830648095.pdf

The mounting style shown on the Specialized in the original post uses a SRAM direct mount standard for S1 type XX FD's.

https://www.sram.com/_media/techdocs/XX_Frame_Fit_Specifications.pdf

Specialized makes a bracket that converts from the SRAM S1 mounting holes to Sram S3 type and Shimano E-type (without the mounting plate).

https://cdn.specialized.com/OA_MEDIA/pdf/manuals/0262_IG_SRAM_XX_FD.pdf

The SRAM XX documentation shows the mounting hole locations for both S1 and S3 type derailleurs. It appears that the S3 type and the Shimano E-type w/o mounting bracket have the same mounting holes.

Does this sound right?


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## swift (Apr 3, 2007)

Good stuff. That' clears it up. ...As much as could be expected anyway.

You'd think some of these bike guys would talk to each other and come up with a standard.


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## unterhausen (Sep 28, 2008)

the nice thing about standards is that everyone can have one


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## Schmitty (Sep 7, 2008)

None of these address the inner/lower cage rub on the tire with short cs's do they?


-Schmitty-


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## rocwandrer (Oct 19, 2008)

Schmitty said:


> None of these address the inner/lower cage rub on the tire with short cs's do they?
> 
> -Schmitty-


maybe not directly, but if you are running 2x, the new 2x specific stuff has more tire clearance.

A downside I have found (that some may be offended by my even saying) is that these can't be "trimmed" by angling the cage, so with 3 position indexed shifters, there can be cross chain positions that rub badly (with the 2x6 setup, I run the big big cross chained combo for short periods of time pretty regularly before triple shifting down to the next ratio when I can reduce the pedaling load conveniently).

Though it goes in the opposite direction as above, it is equally true that you can't cheat the cage out away from the tire a hair with these... at least not nearly as easily as with the tube clamp type.


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## shiggy (Dec 19, 1998)

Schmitty said:


> None of these address the inner/lower cage rub on the tire with short cs's do they?
> 
> -Schmitty-


A 150mm rear hub and matching crankset will solve most of that issue by moving the chainline outboard.


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## smudge (Jan 12, 2004)

the XX derailleurs still seems to have a massive lever on the back side and could potentially interfere with the rear tire. Can anybody speak to this RE chainstay length? Walt?


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## Walt (Jan 23, 2004)

*I haven't seen one yet.*

I should have one to play with in the next couple of weeks. Looking at the pictures, I would agree that the design is not as short-chainstay friendly as the Shimano SLX or XT. But that's just looking at a picture.

Their frame fit specs don't provide a good answer either, as far as I can tell, though they show a "420mm min" dimension for (actual) chainstay length on one of the diagrams. Dimension "M" on page 5 (if you have the docs, email me if you want them) is the distance from the center of the seat tube to the farthest back point on the cable clamp, and it's listed at 40mm for the direct mount. Looks like the cable clamp is relatively centered on the centerline of the bike, as well, so it'll be right in the way of the tire... 

But I haven't seen an actual one yet, so who knows.

-Walt



smudge said:


> the XX derailleurs still seems to have a massive lever on the back side and could potentially interfere with the rear tire. Can anybody speak to this RE chainstay length? Walt?


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## smudge (Jan 12, 2004)

Walt said:


> I should have one to play with in the next couple of weeks. Looking at the pictures, I would agree that the design is not as short-chainstay friendly as the Shimano SLX or XT. But that's just looking at a picture.
> 
> Their frame fit specs don't provide a good answer either, as far as I can tell, though they show a "420mm min" dimension for (actual) chainstay length on one of the diagrams. Dimension "M" on page 5 (if you have the docs, email me if you want them) is the distance from the center of the seat tube to the farthest back point on the cable clamp, and it's listed at 40mm for the direct mount. Looks like the cable clamp is relatively centered on the centerline of the bike, as well, so it'll be right in the way of the tire...
> 
> ...


Please update once you have it, I'd appreciate the info. RE the 420mm min dimension, they didn't specify a reason and my assumption is that it has more to do with cross chaining than tire fit; without referencing a max tire diameter 420mm doesn't really mean anything.

If Shimano made a direct mount double derailleur, I wouldn't even be looking at this as an option. I'm on my last straw with SRAM and if I could avoid it, I'd never buy another product from them.

Thanks Walt.


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## Walt (Jan 23, 2004)

*You can do it w/Shimano*

I have used the SLX/XT (they appear to be identical except for color) derailleur for double setups by simply moving the mount point down a bit (for 29ers, there's a limit to how much you can do this, of course, in order to have the cage clear the chainstays) and then setting the upper limit screw as needed. Seems to work fine with 22 x 32/34/36 setups. I have no idea if you could make it work well with the XX chainring combos and 10sp chain, of course.

I will do some real-world measuring and updating when I have an XX derailleur in hand.

-Walt



smudge said:


> Please update once you have it, I'd appreciate the info. RE the 420mm min dimension, they didn't specify a reason and my assumption is that it has more to do with cross chaining than tire fit; without referencing a max tire diameter 420mm doesn't really mean anything.
> 
> If Shimano made a direct mount double derailleur, I wouldn't even be looking at this as an option. I'm on my last straw with SRAM and if I could avoid it, I'd never buy another product from them.
> 
> Thanks Walt.


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## smudge (Jan 12, 2004)

yo Walt. Where did you get your direct mount XT derailleur? Shimano doesn't even have it in the B2B site.


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## bent steel (Oct 24, 2005)

smudge said:


> yo Walt. Where did you get your direct mount XT derailleur? Shimano doesn't even have it in the B2B site.


Lots of online shops have the, and the QBP # is FD0778.


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## smudge (Jan 12, 2004)

bent steel said:


> Lots of online shops have the, and the QBP # is FD0778.


thanks, but I don't do QBP and I'm fairly confident that Walt doesn't either. Hence the question.


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## bent steel (Oct 24, 2005)

Didn't figure, but also didn't want to preference any particular shop by posting a specific link. Shimano seems terrible about updating their US site.


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## Walt (Jan 23, 2004)

*Bti*

BTI has them:
SH-40638 (XT)
SH-40739 (SLX)

Security has told me they'll have them this summer, as well.

-Walt



smudge said:


> thanks, but I don't do QBP and I'm fairly confident that Walt doesn't either. Hence the question.


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## smudge (Jan 12, 2004)

Walt said:


> BTI has them:
> SH-40638 (XT)
> SH-40739 (SLX)
> 
> ...


Thanks Walt. I thought Security dropped MTB products. Glad they didn't.


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## smudge (Jan 12, 2004)

*tire clearance relative to CS angle*

so, of the two of you who I know have actually done this, assuming that you mitered the ST on center of the BB shell, did you just weld on the mount according to the dimensional specs relative to the centerline of the seat tube?

For 29ers, with a bigger chain stay angle, it would seem that you can mount the derailleur more forward to give a little extra room.

Comparing a 26" bike and a 29er, both with 73° STA, 310mm BB height and 426mm chain stays; the CS angle on the 26er is 3.6° and on the 29er 7.8°.

You could gain about 11mm of clearance by mounting the bolt center of the derailleur mount forward by 11mm (4.2°) on the 29er.

The 29er in this example has a 66.2° angle between the chain stays and seat tube. The mounting envelope for the Shimano direct mount derailleuris 66-69°. If you were to mount the bolt center along the line that's at 69° from the centerline of the chain stays, you could pick up an additional 8mm of clearance for the derailleur. In total, given the hypothetical frame dimensions above, you can move the bolt center forward 18.9mm.

this is good news.

/nerd mode.


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## brant (Jan 6, 2004)

smudge said:


> For 29ers, with a bigger chain stay angle, it would seem that you can mount the derailleur more forward to give a little extra room.
> 
> Comparing a 26" bike and a 29er, both with 73° STA, 310mm BB height and 426mm chain stays; the CS angle on the 26er is 3.6° and on the 29er 7.8°.


That's why put a bend in the seat tubes on production 29ers when I can. See the on-one ti 29er and Ragley TD-1...


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## fanzy4 (Aug 19, 2004)

Here's how I'm doing it for my latest 29er. I've tried to follow the angle recommended by Shimano. It's the slot of the mount (instead of the screw) which ends up aligned with the axis of the ST, which is already slightly offset to the front (by 5mm). I've also put it lower, as it's for a 2x9 drivetrain:


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## Walt (Jan 23, 2004)

*Offset/bent seat tubes*

I've mostly followed Shimanos guidelines regarding chainstay angle relative to the mount, but I have only done these on bikes with offset or bent seat tubes thus far (in fact, only on FS frames - I'll be putting one on a hardtail for the first time in a week or two).

You can certainly offset the derailleur clockwise/forward on most 29ers due to the steep chainstay angle, which makes lots of sense to me. In fact, I would think you have to, in order to prevent weird problems in big/big crosschain situations, and to keep the cage from hitting the chainstay in the granny sometimes as well.

-Walt



smudge said:


> so, of the two of you who I know have actually done this, assuming that you mitered the ST on center of the BB shell, did you just weld on the mount according to the dimensional specs relative to the centerline of the seat tube?
> 
> For 29ers, with a bigger chain stay angle, it would seem that you can mount the derailleur more forward to give a little extra room.
> 
> ...


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