SRAM Red eTap FD chain drop

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JeanMarc
Posts: 16
Joined: Sat Jul 28, 2018 12:34 pm
Location: Montbrison, France

by JeanMarc

Hi there,

I am here because I was searching for feedbacks on "SRAM Red eTap" FD chain drop and I found interesting feedbacks within this website.
In my case the eTap FD mechanism is dropping the chain off the big ring onto the crank arm.
I tried many mechanical adjustments as recommended in this website (*)
Sometimes it's ok, sometimes not. Very strange. Sometimes absolutely fine, sometimes throws the chain off like crazy!
To me it almost feels like a software type problem and not mechanical.

The reason why I am considering this option is developped here after:

As explained by SRAM (https://www.sram.com/stories/11-things- ... m-red-etap) depending on chain position on the cassette, the eTap front derailleur optimizes front shift "quality" by changing how far it moves the chain.

If you are in the large chainring and the large cog (big-big) and you need a lower gear, so you shift your front derailleur to the small chainring;
To avoid pushing the chain past the small chainring and onto the bottom bracket, eTap front derailleurs only move as far inboard as is required to move the chain off of the large chainring and onto the small chainring. A moment after this movement is made, the front derailleur will move the rest of the way to its final position.
I checked that point and that is correct.
I also checked that when you are the large chainring and small cogs, then to shift to the small chainring the eTap software is not applying that "strategy"

Based on the same principle, I also checked that:
If you are in the small chainring and large cogs, then to help pushing the chain in the big chainring the eTap sofware "overshoot" the move before coming back on the right spot.
If you are in the small chainring and small cogs, this "strategy" is not used to shift to the large chainring.

And here is my point : in the last case, I have the feeling that from time to time the FD is "not aware" (eTap system intern com concern?) about the cassette cog in use and would apply the "overshooting strategy" even when small cogs are in used, causing the chain to drop.

Would somebody comment on this?

Thanks in advance

(*)
From a mechanism standpoint, I found quite interesting threads within this website.
Also I read the SRAM instructions,
and watched the SRAM setup videos,
and followed all the steps to the letter
I tried varying the limit screws this way and that by tiny amounts (and larger amounts).
I tried blue thread locker on the limit screws in case the screws were backing out ever so slightly.
I tried tiny rotations and height adjustments of the FD.
If you could do it, I tried it.
Little wedge?, yes I payed a lot of attention to it.
I took the bike back to the LBS mechanics but he was as frustrated as me.
There were no foreign components - nothing to throw a spanner in the works:
Chainset: SRAM RED 110 BCD 50/34T 11 speeds
Cassette: SRAM RED XG-1190 11/32T
Chain: SRAM RED 22 PC-1190 11 speeds
Bottom Bracket : SRAM BB90

Bottom line, nothing could stop occassional and completely unpredictable chain drops.

by Weenie


Jugi
Posts: 443
Joined: Sun Jun 24, 2018 8:10 am

by Jugi

What frame are you using and how long chainstays does it have? What do you have as a rear wheel?

JeanMarc
Posts: 16
Joined: Sat Jul 28, 2018 12:34 pm
Location: Montbrison, France

by JeanMarc

Trek Domane SLR / chainstay is 42cm / Rear wheel is Aeolus Pro 3 TLR
Thank you

kookie
Posts: 56
Joined: Sat Jun 06, 2015 8:43 pm

by kookie

I have come across the same problem once in awhile. I figured the FD goes past the "limit" and returns back to it's normal place. Hopefully this can be fixed through firmware update.

JeanMarc
Posts: 16
Joined: Sat Jul 28, 2018 12:34 pm
Location: Montbrison, France

by JeanMarc

Firmware upgrade? great ! do you know where it is available?
Thanks
JMNs

jih
Posts: 243
Joined: Fri Jan 29, 2016 12:54 pm

by jih

There aren't any firmware updates yet.

It's fiddly to set up, for sure. Are you using the bolt-on stiffener that goes on on the back of the front mech? I've found that with frames that don't allow fitting the stiffener it can be tricky to keep the shifting working nicely over time. It'll work fine for a few months but then eventually go.

kookie
Posts: 56
Joined: Sat Jun 06, 2015 8:43 pm

by kookie

JeanMarc wrote:
Sun Sep 02, 2018 7:41 pm
Firmware upgrade? great ! do you know where it is available?
Thanks
JMNs
I don't think there is an update but I think SRAM should just keep it simple with the shifting.

Yes, eTap for me is pain to setup must be 'perfect'. I don't have much to playwith, there is barely enough room between the FD cage and the crankarm (about a mm) otherwise the crankarm hits the cage.

JeanMarc
Posts: 16
Joined: Sat Jul 28, 2018 12:34 pm
Location: Montbrison, France

by JeanMarc

jih wrote:
Sun Sep 02, 2018 8:14 pm
There aren't any firmware updates yet.

It's fiddly to set up, for sure. Are you using the bolt-on stiffener that goes on on the back of the front mech? I've found that with frames that don't allow fitting the stiffener it can be tricky to keep the shifting working nicely over time. It'll work fine for a few months but then eventually go.
Yepe, I call it the wedge in my first post

Thank
JMns

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wheelbuilder
Posts: 631
Joined: Wed Feb 08, 2017 2:10 am

by wheelbuilder

The best thing I did for the performance of my etap Fd was installing a wedge. Crisper, faster front shifts, and zero derialleur "migration" from it's optimal position. Its kind of labor intensive to install one though, as you have to choose the correct wedge that will contact the seat tube EXACTLY where you need it to be while at the same time ensuring the FD is perfectly oriented. Lots of sliding the wedge around and futzing with the derailleur, but if you get it right it works really well. I know this doesn't help OP, but it is relevant to set-up and performance.

Jugi
Posts: 443
Joined: Sun Jun 24, 2018 8:10 am

by Jugi

JeanMarc wrote:
Sun Sep 02, 2018 5:49 pm
Trek Domane SLR / chainstay is 42cm / Rear wheel is Aeolus Pro 3 TLR
That is not an ”edge case” bicycle by any means, so it basically should work.

What is the general condition of the chainrings and chain? Weared chainrings can exhibit just the type of shifting behaviour you described, but I take it they are as new as the whole groupset.

If you want to investigate the possibility of the shifting logic failing in the RD (the FD ”overshoots” the shift too much while the chain is on the smaller sprockets), connect a Garmin Edge (or similar device which understands ANT+ gearing status) and check what the RD is giving out as the RD sprocket information. If you get the correct sprocket status, I don’t think the shifting logic can be the culprit.

JeanMarc
Posts: 16
Joined: Sat Jul 28, 2018 12:34 pm
Location: Montbrison, France

by JeanMarc

Jugi, That's a brilliant proposal. I will do so and keep you posted.

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wheelsONfire
Posts: 2730
Joined: Mon Jul 07, 2014 8:15 am
Location: NorthEU

by wheelsONfire

I have no such issues on my bike.
It shouldn't matter, but i use 50/36. I have no use for a 34T chainring.
My setup doesn't throw off the chain no matter what gears i use shifting up/down.
Chainstays = 403mm.
(Ofcourse i use the wedge.)
Bikes:

Ax Lightness Vial EVO Race (2018.12.21)
viewtopic.php?f=10&t=156137
Paduano Racing Fidia (kind of shelved)
Open *UP* (2016.04.14)


Ex bike; Vial EVO D

TobinHatesYou
Posts: 3538
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

With round rings, it shouldn't be that hard to eliminate the thrown chains. Consider this angled shim if you have a 50t big ring. That will drop the tail of the cage so it more closely follows the circumference of the 50t.

When I tried putting oval rings back on, there was about a quarter turn of the limit screw between the ramps not being able to pick the chain up onto the big ring at all vs throwing the chain up and over. The worst chainline for this was with the chain in the 6th or 7th cog, the most reliable was the 11th cog. It's perhaps exacerbated by the overshifting programming, but I think the Yaw cage shape just creates too big of a gap between the outer cage and chain when it's "centered" on the cassette. This can be partially remedied by rotating yaw-ing the tail of the cage inward past recommendations, but that means you will get a ton of cage rub should you ever use a combo like 1x9. It also makes shifting to the big ring very laggy/lazy.
Last edited by TobinHatesYou on Mon Sep 03, 2018 7:15 am, edited 1 time in total.

alcatraz
Posts: 2049
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Check your crank for sideplay. Maybe your rings are moving sideways a lot.

by Weenie


JeanMarc
Posts: 16
Joined: Sat Jul 28, 2018 12:34 pm
Location: Montbrison, France

by JeanMarc

Thank you everybody for all of your replies
To Jugi,
I checked what the RD is giving out as the RD sprocket information. The Sigma system displays the correct sprocket status, so we can assume the shifting logic is not the culprit. As a result I am back to a mechanical fine tuning cocncern.
I am curious though as to what limits/manages the overshoot travel because as far as I can understand, the little limit screw is set + acting with the FD cage in its stabilized spot (I mean once the overshoot phase is over).
To wheelsOnfire,
Tank you for sharing your positive experience with a 50/36 chainring + a 403mm chainstay and we both use the wedge.
To TobinHatesYou,
The tilted shim makes a lot of sense to me. I will figure out how to order one.
Also, rotating the cage in-ward is something I need to test (and it will give more clearance between the cage tail and the crank arm)
To alcatras,
You are right, double check the crank sideplay is always a good thing to do. So far, so good as the bike is less than 1500 miles.
I attached two photos I took after a chain drop; one can see the highest tooth location vs the cage mark (note that repeating chain drops will result in damaging the Quarq Powermeter battery thingy)
One more time thank you for your support
Attachments
IMG_1560.JPG
Chain drop
IMG_1561.JPG
Teeth vs cage mark

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