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lower front derailleur for smaller crank

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lower front derailleur for smaller crank

Old 12-06-20, 04:53 PM
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sean.hwy
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lower front derailleur for smaller crank

I replaced the OPI SpideRing, 52/36 with a 46/30T on my 2019 systemsix to help with hills where I live. I injured both knees in a motorcycle accident in oct 2016. Going from 36T to 30T has helped a lot.



I adjusted the front derailleur as low as it will go. The specs call for 1mm to 3mm. In the picture that's a 5mm allen wrench.



I want to replace this bottom bracket with one that goes down another 2mm. I don't know the correct name to look it up or even if is possible.







Or do I need to sell my bike and buy a bike that has round seat tubes that take this kind of front derailleur that allows easy adjustments?


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Old 12-06-20, 05:23 PM
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Can you lengthen the slot with a round file (chainsaw?) a "few" mm?
Braze on vs Clamp on.
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Old 12-06-20, 05:34 PM
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https://wickwerks.com/products/fit-link-adapter/

https://shop.fullspeedahead.com/en/a...ompact-adapter
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Old 12-06-20, 05:58 PM
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If your bike shifts satisfactorily here is no need to change anything. Never Fix A Running Piece.
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Old 12-06-20, 07:47 PM
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Originally Posted by dsbrantjr View Post
If your bike shifts satisfactorily here is no need to change anything. Never Fix A Running Piece.
^ This

The gap rules get thrown out if you run a chainring that is technically smaller than recommended (derailleur cage curvature). At least I throw them out and set the derailleur a bit higher to get good shifting.

If it shifts well, and doesnít drop the chain, donít sweat it.

John
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Old 12-06-20, 08:07 PM
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It's not a smaller crank, it's a crank w/ smaller chainrings. It's not a bottom bracket, it's a braze-on mount. Also judging by the cable tension screw and the way the cable is not tucked under the cover I'm guessing your front derailleur isn't set up ideally.
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Old 12-06-20, 11:05 PM
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Jeff Wills
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If you lower the derailleur, will the tail end of the derailleur cage hit the chainstay? I have a bike like that (36-24 double on a cargo bike). The front derailleur is 10mm above the chainring and it works fine.

As above- if it works, don't fix it.
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Old 12-07-20, 12:22 AM
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Originally Posted by 70sSanO View Post
^ This

The gap rules get thrown out if you run a chainring that is technically smaller than recommended (derailleur cage curvature). At least I throw them out and set the derailleur a bit higher to get good shifting.

If it shifts well, and doesnít drop the chain, donít sweat it.

John
It does not drop the chain. It easily changes gears going up or down. The issue is there is a slight chain rub in 1st (30T & 30 ) or 22nd (46T & 11 ) gear. I can adjust it to not rub in first gear or 22nd gear. not both. It's just an ever slight rub. My annoying than anything.

5mm gap is ok then ?
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Old 12-07-20, 08:58 AM
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Originally Posted by sean.hwy View Post
It does not drop the chain. It easily changes gears going up or down. The issue is there is a slight chain rub in 1st (30T & 30 ) or 22nd (46T & 11 ) gear. I can adjust it to not rub in first gear or 22nd gear. not both. It's just an ever slight rub. My annoying than anything.

5mm gap is ok then ?
I don’t see a problem with 5mm, but I hate chain rubbing, even if it is slightly.

There was a time when Shimano used a screw at the bottom end of the cage to attach the front and back cage plates together. If a derailleur cage was just a hair too narrow you could back out the screw a put a small washer in between the two plates and slightly widen it to give a bit more cage width. Put the screw back in. If you can do this it might help.

But, because you have pushed both chainrings to a sub-compact (smaller) size, you might want to consider a derailleur that is better suited for your setup.

FSA makes a Super Compact Adapter to lower a front derailleur when using a braze-on. I’ve never used it but it looks like a solution, a bit tinker toy, but still a solution.

I don’t know the specific double FD for a 46/30 since I have used triple FD with a 30t (42/30). Ironically it is also braze-on with 8mm gap using a triple FD. But it is a a flat bar conversion so shifting performance was not a consideration.

I’m sure someone here can make a better suggestion.

John

Last edited by 70sSanO; 12-07-20 at 09:10 AM.
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Old 12-07-20, 07:44 PM
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Originally Posted by Jeff Wills View Post
If you lower the derailleur, will the tail end of the derailleur cage hit the chainstay? I have a bike like that (36-24 double on a cargo bike). The front derailleur is 10mm above the chainring and it works fine.

As above- if it works, don't fix it.
I have it adjusted all the way down.
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Old 12-07-20, 07:53 PM
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The FSA site was sold out and several bike websites. I found someone on ebay and place an order. It will arrive next week.

This is my first road bike. I now know better what to look for so I don't buy another snow flake that has so many special parts. Since my crank uses a funky spidering engagement I could not just buy an off the shelf sprockets that bolts to the crank with for 4 or 5 bolts. I has to special order my chainring from England. No one state side had a 46T/30T.

My top stone gravel bike is 100x easier by comparison. clamp on front derailleur, FSA crankset with standard four bolts to hold on the sprockets.

Tempted to sell my road bike and just slap on some good carbon wheels on the gravel bike when I want to do just road.
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Old 12-07-20, 10:17 PM
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Brings up an observation: I have a SRAM Force 10 FD and it had two mounting holes, one for conventional and the other for compact. Replaced it with a Red 11 yaw, and it has only one hole. Maybe in the time of 11 the assumption is all braze on mounts allow for compact cranks? I contemplated opening up the slot some on the braze on, but was too lazy in the end and just accepted that the FD is a little high. But 5mm I don't know, I don't think they just list the spec to justify their paycheck.

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