# Shimano CX70 Front Derailleur on MTB



## HiddenStar (Apr 17, 2010)

Hi, does anyone know if the Shimano CX70 FD works on an MTB with MTB chain rings (i.e. not road compact crank)? At 102 grams for a FD with a 34.9mm clamp, I'm considering it as a viable option to replace my current XT one given that it handles top pull as well.

I have actually tried using the SRAM Red FD with a speen adaptor. Disappointingly, it doesn't work very well as I am using the 2 outer most chain rings of my MTB crank set and alot of force is required to shift the chain from the middle to big chain ring. 

Thanks in advance


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## Rallyator (Nov 11, 2008)

Sure it works, some dremeling will be needed though. I'll post some pics ASAP. This might help. Cheers.


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## HiddenStar (Apr 17, 2010)

Thanks, I'd appreciate the photos as I cannot really understand the spanish forums even after google translation :/

Btw, care to share also what kind of dremeling wil be needed? Thanks


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## Rallyator (Nov 11, 2008)

Sorry for the delay in posting the pics, here they are:















I suggest you apply some nail polish to avoid rust.


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## HiddenStar (Apr 17, 2010)

Wow, that's alot of filing/dremeling to do. Is the force required to shift from the inner to outer chain ring alot?


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## Rallyator (Nov 11, 2008)

The spring has a bit less tension than standard Shimano mtb mech's, so shifting becomes a pleasure :yesnod:. Really works.


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## HiddenStar (Apr 17, 2010)

Ahh, thanks alot for your pictures and sharing, I shall try it soon


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## Nozes (Feb 18, 2008)

Hi guys,

I'm running a 3x9 with XT shifters. I'm thinking about going 2x9 with this FD,any mods needed? The BB is 68mm,so I think the chainline issue won't be a problem (expecting some minor chain rubbing on big chainring/small cog also).

Thanks!


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## HiddenStar (Apr 17, 2010)

@Nozes: As you can see from Rallyator's pictures, that's the amount of filing/dremeling you needa do (minimally).

I just managed to get mine working after alot of filing (wish I had a dremel). In fact, I had to file down the inside portion of the FD too (where the metal touches the limit screws) in order to get the FD to shift further out. I think this is because I'm using the 2 outermost rings of a triple MTB crankset. Mine still has chain rub on certain combinations though.

Rallyator, does your set up have any chain rub on extreme cog/chainring combinations? And I presume you are using a double MTB crank? I'm wondering if using a double crank will improve the chain alignment... can anyone help? Thanks


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## bobi.k (May 26, 2008)

The chainline should be 43.5 mm. The outside ring should be 50 mm from the middle of the frame at most. It is made for road crankset so it doesn't go out very far. I have specialized mtb crank and double setup on my Stumpjumper HT with 22 and 38 rings and it works perfectly.


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## HiddenStar (Apr 17, 2010)

Ahh, bobi.k, you didn't need to do any modifications to the FD? No chain rubs on any combination?

You mentioned that the outside ring should be 50mm from the middle of the frame at the most, is that how your crank is set up? I'm basically trying to see if it's worth it for me to change to a double crank. Thanks


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## bobi.k (May 26, 2008)

Mine is 49 mm but the FD is not jet in the outmost position. It has 2 or 3 mm more space. Nothing is filled dremeld or modified. It just works.


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## HiddenStar (Apr 17, 2010)

Thanks for the pict  Nice that you got it working so easily! Looks like my problem is having to want to use the big (i.e. 40T upwards) and middle chainrings as opposed to the middle and granny...

Maybe the question I should be asking is: Is the big chain ring (i.e. 40T and above) of a double specific crankset closer to the BB as compared to that of a triple, and if so, by how much?


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## bobi.k (May 26, 2008)

Double specific crankset chainline should be close to 45mm or less. XX chainline is 49.5 mm so the big ring is 52-53 mm. http://cdn.sram.com/cdn/farfuture/U...default/files/xx_frame_fit_specifications.pdf
But on the triple spider you can mount 40+ ring in the place of middle chainring. They have the same BCD. Lots of companies sell 40+ chainrings for middle mount. I know Specialites do Couronne Chinook VTT DuLight.fr - Le spécialiste des composants légers pour toutes les pratiques du cyclisme.
So your chainline will be around 44 mm. Just bare in mind that difference in chainrings size can be 16 tooth or less. 
And be careful that your granny ring don't touch chainstay.


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## HiddenStar (Apr 17, 2010)

You totally read my mind  My current set up is 44T-32T (Outer - middle position with the granny position left empty). And I actually just ordered a 29T (to effectively replace the 32T) chainring (with a BCD for the granny position) to be paired with my current 44T chainring which I will move to the middle position.

That will make the difference 15T, and I'm crossing my fingers that shifting performance will not be affected. You mentioned that the difference should be kept at 16T and below, but do you think at 15T, shifting performance will deteriorate slightly?


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## bobi.k (May 26, 2008)

No, it is made for that. 16T difference means that at this ratio it will still work flawless. In extreme, it works also with 18T difference but than you must shift carefully and the ramps on the big ring must be good. I tried 42-24 and it was O.K. Just not good enough for racing. To dangerous for chainsuck on down shift. With extreme shifting the chain would miss the small ring and fall between frame and crank.
No such problem with 38-22 setup. My cassette is 11-32. Weight reasons obviously.


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## HiddenStar (Apr 17, 2010)

Alright, good to hear! Appreciate your help bobi.k


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## HiddenStar (Apr 17, 2010)

Ahh sigh, had a disappointing attempt today. Unfortunately, the 44T ring (when mounted at the middle position) is too big and hits the frame because the shifting pins on the chainring cannot clear the chainstay. I'm using a scott scale btw. Is that the reason why I can't really find double MTB cranksets around with 44T as the biggest chainring?

I'm thinking of trying a 42T instead but I'm wondering if it's even worth a try...


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## bobi.k (May 26, 2008)

42T should clear the chainstay. Which crankset do you have. Can you put a spacer on the drive side? SRAM cranks have spacers on drive and non drive side. You can play with them. Or if you have threaded BB you can also put spacer on the drive side.


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## HiddenStar (Apr 17, 2010)

I'm using an Aerozine crank. I'm trying not to touch the external BB by placing spacers for because I don't have the tools to remove the BB haha. Ok, will consider getting a 42T ring... more costs yikes


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## HiddenStar (Apr 17, 2010)

An update: Some pictures to show how I managed to get the CX70 working... 93.6 grams including the carbon clamp, a pretty good alternative for a road FD + speen set up. Some filing had to be done to get the FD to shift all the way to the outer most chain ring of the triple crankset (I painted the filed portions with nail polish, so it's kinda hard to spot in the picture). However, it is easier to shift as compared to the SRAM red + speen (if you can get that to work well enough).



















I have decided to wait for an appropriate time to change my crankset to a double one so that the chainline will be improved


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## bobi.k (May 26, 2008)

O.K. good job. But your big chainring is not properly installed. You should rotate it, so the catch pin is aligned with crank. It will also shift better, because the ramps on chainring are calculated for this position.

BTW, nice sandals!


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## HiddenStar (Apr 17, 2010)

Lol! Those are my mum's. Anyway, really sharp spotting there! Now that you mention, I didn't even realise the chain ring was mounted wrongly. Thanks!

I suppose there's no special alignment for the middle chain ring... or is there?


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## bobi.k (May 26, 2008)

There should be a mark on it like a tooth. You can see it on this picture on the left inner side.
https://www.chainreactioncycles.com/Images/Models/Original/38184.jpg

Obviously aligned with crank.


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## HiddenStar (Apr 17, 2010)

Ahh, yea I did a check and both the large and middle chain rings were coincidentally aligned in the same orientation but just not in phase with the crank arm, which explains why my shift quality has not been affected. Either way, a catch pin that is not hidden behind the crank arm is a little ugly, so I'll make the necessary adjustments tmr.

Thanks again for the help bobi.k


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## jadis3 (Nov 18, 2007)

I am using CX70 with an XTR 42-30 with very little treatment by a file.
As a gear shifters the sl-r780 road flat handlebar levers are used, they are smooth.


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## benmills (Sep 25, 2013)

I'm a little confused. Would the CX70 derailleur work with regular mountain bike shifters (I'm thinking about SRAM X7 or X9 shifters)?

In my case, I have a hybrid flat bar bike that I want to update with a cyclocross 36/46 crankset. I've been having a tough time finding a derailleur/flat bar shifter combo for this kind of crankset. Most MTB derailleurs seem to be for smaller MTB cranksets and road derailleurs seem to be for road shifters only (and want at least a 50 big ring).


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## mtb_jeremy (Jul 22, 2004)

I just built up my bike with this front derailleur, and have a very minor issue with it. The bike is a Ritchey P-650b (17"), XTR M985 cranks (42x30), XTR M980 cassette (11-34), and XO 10-speed Gripshift. Compatibility with shifters is fine for me.

The minor issue I have seems to be the the precision needed to make 10-speed work. My problem is seen when I am I get to big ring in the front and smallest cog in the rear (chain all the way to the outbound side of the bike) and get rubbing of the chain on the derailleur cage. The same is true for the small ring on the front and the big cog in the rear (chain at most inbound position to the bike). It works otherwise, and the only issue is some noise from the chain rub at these extreme ends of the spectrum. My conclusion is that this comes from the fact that this front derailleur cage is designed for a crank with a 46-36 front ring combo. If you look at the Sram front derailleurs there are different models for "compact" (36 and 38tooth) cranks and bigger gear (40 and 42 tooth) cranks. It shows me that the drive train is getting so precise that minor changes in the cage are needed to work perfectly.

I like the CX70 front derailleur (light, sturdy, looks nice), and could live with based on the gears I use the most. Ultimately I am going to be swapping it out for a mountain bike model just to have 100% flawless operation .


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## donnieboy (Jan 20, 2014)

*I'm using the same xtrm985 42/30 crank and cx70 deraileur is on it's way*



jadis3 said:


> I am using CX70 with an XTR 42-30 with very little treatment by a file.
> As a gear shifters the sl-r780 road flat handlebar levers are used, they are smooth.


Our setup will be similar in 3 ways:
10 x 2
Cranks are both XTR m985 42/30 (Chainline 48.8mm)
I've ordered the cx70 FD (Chainline 43.5mm)

The difference with my setup will be I have 10 speed Ultegra STIs and a Wolftooth tanpan to convert the rear cable pull from Road shifter to MTN deraileur. Should be fun but I'm nervous about the front deraileur until it arrives and I have it tested. I suspect there may be rub on highest gear combo, but I'm playing outside Shimano's sandbox, so that's just how it may go. I'll post up progress.


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