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front derailer hitting chain stay

Old 08-13-21, 09:02 PM
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schnurrp
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front derailer hitting chain stay

Changing a Trek 1500 SLR from a road bike into a hybrid for use on the Raleigh, NC greenways, I wanted to change the triple Sora chain set into a two way, 28/38. This means I have to slide the derailer down the seat tube to work on the 38 t from its original higher position for the stock 53 t. When I did this the lower tip end of the derailer contacts the chain stay when it moves in to try to shift to the smaller chain ring. Is there any solution for this?

Also the curve of the derailer is quite different from the curve of the smaller 38 t chain ring.
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Old 08-13-21, 09:56 PM
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Well not exactly, at least how I set up a double that was a triple. Although some might disagree.

I start out “about” where I would set it as if the outer chainring was still there, which means you’ll have a lot larger gap between the 38t and the front derailleur cage.

What I want is to line the derailleur plates at the best position to shift from the 28t to the 38t and back again. If I am concerned I’ll drop a chain, I usually install a chainguard in the outer position. I’ve only done that on mtb’s.

It may take some tweaking, but it has worked well for me.

John
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Old 08-13-21, 10:12 PM
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Another derailleur or hack off and weld.
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Old 08-13-21, 10:40 PM
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I would switch to a road FD, or even better, one designed for smaller chainrings for cyclocross, like the Shimano CX70. The cage on triple derailleurs extends lower to accommodate the granny ring.

The SunTour ARX I'm using with my 42/28 double leaves about 3mm clearance to the chainstay. So a 40/28 double would most likely work without making anything more complicated. And that FD can be found pretty cheap!
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Old 08-14-21, 06:56 AM
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I decided to buy a

SHIMANO XT FD-M8020-D 2x11 Front Derailleur and clip. I'll let you know how it works out.


Thanks for your suggestions.
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Old 08-14-21, 07:21 AM
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Since I don’t know what front shifter you have/were going to use, I’m assuming you did your homework on cable pull.

With a 2x, you can sometimes fudge it a bit if you have more than you need, but if it is less it won’t get there. It is academic if a friction thumb shifter is being used.

John
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Old 08-14-21, 10:39 AM
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Have you tries just raising the derailleur so it clears the stays?

XT front derailleur will not work with Sora shifters.

ive had good luck with Sora R3k, 28/38 Deore M6K cranks, and Ultegra 6700 front derailleur

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Old 08-14-21, 12:57 PM
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Originally Posted by DorkDisk View Post
Have you tries just raising the derailleur so it clears the stays?

XT front derailleur will not work with Sora shifters.

ive had good luck with Sora R3k, 28/38 Deore M6K cranks, and Ultegra 6700 front derailleur

Look at the picture. It doesn’t take a mental giant to see that if a triple front derailleur that can shift just the middle and inner chainrings without lowering it, it can equally shift a double if the rings are “close enough” to the derailleur spec.

I’m running an early 80’s Suntour Cyclone double with a 42/30. It is friction so I don’t have to worry about cable pull, but I’m also using flat rings.

John
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Old 08-14-21, 01:20 PM
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Originally Posted by 70sSanO View Post
Look at the picture. It doesn’t take a mental giant to see that if a triple front derailleur that can shift just the middle and inner chainrings without lowering it, it can equally shift a double if the rings are “close enough” to the derailleur spec.

John
Who, me? I don't have any issues with my drivetrains.
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Old 08-14-21, 01:47 PM
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Originally Posted by DorkDisk View Post
Who, me? I don't have any issues with my drivetrains.
No, definitely not you.

Your pic is a great example of how to set up a smaller chainring double with more gap above the chainring.

The only thing I did, as a pre-caution, was add a bash/chain guard in the outer position on my mtb’s because of rough terrain and the potential of dropping a chain on the outside.

John
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Old 08-14-21, 04:19 PM
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Since we're sharing pictures, here's mine.



As it's a "road" front derailleur, I don't have to set it abnormally high over the big ring -- it's at about 2mm.
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Old 08-14-21, 04:44 PM
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Originally Posted by ThermionicScott View Post
Since we're sharing pictures, here's mine.



As it's a "road" front derailleur, I don't have to set it abnormally high over the big ring -- it's at about 2mm.
That is pretty impressive for a 42/28.

Not sure of chainstay angle and the FD specs, but nice job!

John
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Old 08-14-21, 07:45 PM
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Originally Posted by 70sSanO View Post
That is pretty impressive for a 42/28.

Not sure of chainstay angle and the FD specs, but nice job!

John
Thanks! The frame has a 73° seat tube angle and 60-65mm of bottom bracket drop. I was only a math minor in college, so I don't know if I could figure out the chainstay angle without some help.
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Old 08-14-21, 09:04 PM
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Just wondering.

John
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Old 08-15-21, 06:17 AM
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How far above the front chain ring can a derailer be installed without sacrificing function?
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Old 08-15-21, 08:38 AM
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Well my flat bar conversion with the old Cyclone road FD and 42t is at 6mm.

My Serotta mtb with Columbus MAX tubing that gets more oval at the dropout wouldn’t let me get closer than 25mm with a 34/24. And even then I had to sand the clamp a bit to fit.

I’d either start as close to the chainstay and move up if needed, or close to the original location for the triple and move down.

One caveat, large gap and large chainring is the kiss of death. Inner-middle only, seems to work fine; or maybe a low 40’s tooth ring and below.

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Old 08-15-21, 11:49 AM
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Originally Posted by schnurrp View Post
How far above the front chain ring can a derailer be installed without sacrificing function?
There's no single answer. It depends on the specific derailleur and the tooth count range it has to span when shifting. In general, you want it to be pretty close; within a few millimeters.
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Old 08-15-21, 12:27 PM
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Originally Posted by JohnDThompson View Post
There's no single answer. It depends on the specific derailleur and the tooth count range it has to span when shifting. In general, you want it to be pretty close; within a few millimeters.
The problem is, in most cases, you can’t get to a few mms above the middle chainring after you remove the outer chainring on a triple and only use the inner-middle rings.

I imagine there are specific derailleurs for smaller inner-outer/(old middle) and small chainring doubles.

It is like setting the FD high limit to only shift the inner and middle positions, leaving it in the same place, and lock out the outer position. You’ll go happily along having no clue that the FD now sits an inch above the middle ring.

The caveat, I believe, is a potential issue with throwing a chain off the middle/outer ring because the FD is so far above the chainring.

I never lost a chain on my mtb without a chain guard, but trying, but not always succeeding, to not do something stupid, I thought it might be prudent to add one in the outer position.

As demonstrated above a double road FD, at least older ones, seem to work, but maybe not be compatible with index STI/trigger shifters.

John

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Old 08-15-21, 12:43 PM
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is there really a need to do this? what triple sora does OP have? what are the chain rings?

current Sora is 53/39/30 which is pretty close to 38/28

why not just keep it a triple if really wanted get newer crank or change the rings

what is the advantage for going 2x vs 3x ????
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Old 08-15-21, 03:25 PM
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Originally Posted by 70sSanO View Post
The problem is, in most cases, you can’t get to a few mms above the middle chainring after you remove the outer chainring on a triple and only use the inner-middle rings.

I imagine there are specific derailleurs for smaller inner-outer/(old middle) and small chainring doubles.
With the growing popularity of "compact" cranks, I wouldn't be surprised if someone offers a front derailleur with a shorter cage to allow it to sit closer to the chainrings.
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Old 08-15-21, 03:44 PM
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Originally Posted by JohnDThompson View Post
With the growing popularity of "compact" cranks, I wouldn't be surprised if someone offers a front derailleur with a shorter cage to allow it to sit closer to the chainrings.
I agree. I’m not up to speed on the more current offerings.

And I really do respect your opinion.

John
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Old 08-15-21, 04:00 PM
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IRD Sub-C FD at least to 10 speed
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Old 08-15-21, 04:09 PM
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Originally Posted by JohnDThompson View Post
With the growing popularity of "compact" cranks, I wouldn't be surprised if someone offers a front derailleur with a shorter cage to allow it to sit closer to the chainrings.
That's why I suggested the CX70 front derailleur upthread (assuming one could still be found.) It's designed specifically for a 46/36 cyclocross double.
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Old 08-15-21, 06:30 PM
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Originally Posted by ThermionicScott View Post
That's why I suggested the CX70 front derailleur upthread (assuming one could still be found.) It's designed specifically for a 46/36 cyclocross double.
I am using the CX70. Though not spec'ed as a triple FD, it works fine.

My bike's original derailler was a Shimano Deore for a 48-38-24 triple. Many years later, I went to a 42T big ring, and I could not lower the Deore enough without hitting the chain stay. The Deore still shifted okay, but looked crazy high over the now-smaller big ring.The CX70 had a shorter/less tall cage and worked just fine with the 42T. Lately I have put a 46T on the outer ring position and had to raise the FD up a bit to accommodate it. The CX70 works just fine with it too.

But the simplest solution, already mentioned, would be to keep the original derailler and just trim the outer limit screw to prevent overshoot, and maybe put on a bash guard for aesthetics.

I understand that the OP has already made his move. Best of luck.
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Old 08-15-21, 09:23 PM
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My bike before I started modifying was 52-42-30. I knew the style of riding I was going to do on the paved greenway trails would be maybe 12-14 mph max (trails are shared with walkers) but the trails can be quite hilly so climbing ability is important. But you are right it's not that much different.
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