noodle soup

what don't you understand?

eTap won't work with a compact crankset, on a bike that previously was set up that way.

GlennR

What am i missing?

I had Red mechanical with a compact and 11-28 and eTap works great.

noodle soup

Danny01's Kestrel Talon works fine with a compact crankset and mechanical components, but won't work with Etap. I would say that's a design flaw of eTap.

There's no way SRAM intentionally designed it to only work with select frames, and not others. If SRAM used the same mounting parameters as mechanical front derailleurs, there wouldn't be these problems.

I doubt the next version will have the same issue.

GlennR

They seemed the same to me.

My bike wasn't designed for eTap and in fact I had to special order it with Red 22 since it was only offered with Shimano in a stock build.

noodle soup

They should be the same, but if eTap doesn't work on some frames that have no issues running mechanical, SRAM clearly didn't use the same mounting parameters.

This was a topic of conversation at NAHBS last year, and a question people had about the FSA electronic groupset this year.

nycphotography

Is there a precise spec for front hanger height? Are these frame clearly within that spec, or did they just happen to work because older groupsets were more forgiving of poor frame compliance w/ specs and/or quality control? Or, are these frames clearly within spec and SRAM has failed to account for the full range of the spec in their engineering?

The fact that it works on most frames but not all doesn't automatically condemn SRAM's engineering. In fact, whether it would seem to indicate the frames are out of spec, or the groups are out of spec has for more to do with whether you work for the frame builders or the group makers. We know where your loyalties lie, which colors your perception and has to be backed out of anything you say before it can be considered.

Seeming to indicate something is far from conclusive. More information is required to really know.

nycphotography

They should be the same, but if eTap doesn't work on some frames but has no problem working on others, then those frame clearly didn't use the same mounting parameters.

This may have been a topic of conversation at NAHBS last year, but I bet it was a conversation between frame builders, since SRAM is unlikely to debate themselves in public.

noodle soup

The frames came first, and worked fine with existing mechanical components.

eTap is the problem, but SRAM fanboys will never admit it is flawed. Have you ever wondered why it's not common on gravel bikes?

noodle soup

SRAM clearly did not design the eTap front derailleur, with the same mounting parameters that they use for mechanical front deraileurs. That is the problem.

GlennR

If you say so, I have no proof to the contrary. Or are you relying on #fakenews ?

Danny01

The problem exists on frames with etap. The problem does not exist on frame without etap, be it di2, SRAM or shimano mechnical. Even though etap works fine on most frames, the fast that the problem exists only when etap is introduced shows us that it is a design problem with etap and not the frame.

Danny01

You can clearly see that there is a portion on the front derailleur housing that sticks out over the top on the hanger. That part that sticks out hits the top of the hanger, reducing its ability to be mounted lower. On di2 front derailleurs, the side of the housing that meet the hanger is completely flat as to not hinder downward movement of the derailleur.

noodle soup

Yep.

I would be very surprised if SRAM doesn't fix this on the next version, but that doesn't help you now.

GlennR

So you're saying that on some frames with a compact crank, you can't get the FD close enough to the 50T chainring.

OK... i can see that. Thanks for proving your point and accept my apology for the #fakenews.

Marcus_Ti

Well, I'll be damned. That is the second or third design flaw in the form of the FD....or maybe they plan on people having movable collar bands for their FD. Talk about an oversight.

The other being the battery wart sticking out the back and impacting tire clearance....Gravel Cyclist asked them about fixing that one...and they basically said it is a "feature".

Other other one...being the width causing the FD to block certain crankarms with narrower Q-factors (IIRC some Shimano road cranks are like that)....remember seeing pictures on WeightWeenies.

nycphotography

I notice frame builder boy didn't answer the question about whether the frames are within spec for hanger location and instead just used an illogical argument to prove fault. Why illogical? Because the exact same logic can be used to prove the opposite fault.

So now I'm going to be a di$k and point out some basic facts about engineering and compatibility. I am in no way claiming to know whether this is SRAM's fault or the frame builders fault. All I am going to do is point out how it COULD be the frame builders fault, and how it also COULD be SRAM's fault.

First, either the frames are in spec, or they are out of spec. If they are out of spec, then it is not SRAM's fault they did not accommodate those frames with this groupset, regardless of whether or not previous groupsets worked. If the frames are in spec, this this is clearly SRAM's fault for not working with these in spec frames.

Funny, mr frame builder avoids my very simple question about if the frames are in spec. Wilful obfuscation perhaps?

Now, let's assume there IS no spec for hanger location, and these things have just more or less worked by sloppy chance. IF this is the case, there will be an average mounting location and a (usually standard) deviation of mounting locations, measurable across the universe of frames w/ fixed location hangers. The distribution can be standard, or it can be skewed. Lets assume that it is reasonably standard. A good old fashioned bell curve.

In this scenario, it seems pretty obvious to anyone with even a basic education, that if you want your frame to work, you better put your hanger dead in the middle of that range, and if you can't do that, that you better at least get it within the first standard deviation of that average location. If you fail to do that, then you are taking compatibility risks they may come home to roost.

Now assuming the lack of a standard, this becomes a slightly different problem for SRAM, because in this scenario they are not controlling the entire universe of frames produced, they are stuck trying to accommodate a literally unbounded range of frames. They can't literally measure every frame ever made and know what the worst possible frame builders have done. Instead they have to randomly sample a selection of frames, and not so randomly sample some that they really really care about, and then make some educated guesses about what range of sloppiness they need to account for. Because make no mistake about it, producing a frame with a fixed hangar in a location more than 1 std deviation from the mean is just plain sloppy. If it happens to work, hey, you got lucky. But it in no way proves you exercised even minimal diligence in designing the frame. So now SRAM has come up with a range that hopefully covers at least two standard deviations of sloppiness. They prototype it and test it on a test rig to prove those "design extremes" work, then they real world test it with as many frames as possible to prove they all work. But they cannot reasonably be expected to test it with every single oddball frame ever produced. But if every oddball frame builder does their diligence and nails the dead middle of the range (the average), then their oddball ish will work.

So IF there is no spec for front der location, now the question becomes, what is observed variation across a sample of the universe, and does the group work within some reasonable tolerance therein?

Finally, often in engineering teams, there is some guy who's been around forever who knows crap like this. He is usually unpopular. The kids can't stand him, because he always sees immediate issues with almost any innovative idea, and that damps their enthusiasm. Human nature being what it is, they seldom understand the immense value he brings to the team by identifying issues early so they can be addressed. Eventually, the crufty old guy leaves, retires, finds something else to do, gets marginalized to some unrelated department, or gets forced out.

The kinds of things the old guy tends to know are things like "you realize of course, that between 1999 and 2015, frames based on the original bla bla design have unusually high hangers, so make sure you include a few in your sample". Of course the kids have not the first clue about anything like that. I mean that was way back in the dark ages!

Now I don't know what happened here. All I know is the same exact thing everyone else knows: there seems to be a compatibility problem.

Now somebody knows if there is a spec for front hanger location. But the one person here who would be most expected to know is staying suspiciously quiet on that point. My BS/fake news/spin detector tells me that he knows there is a spec and that these frames are out of spec but he doesn't want to admit that because maybe his employer is affected by this as well.

But the reality is, until we get more answers / information, nobody here really knows who to blame. Anyone who claims to know conclusively without answering the above is either lying / spinning / protecting their interests, OR they are just clowning themselves. Because if they had evidence which could prove SRAM missed the published spec, you can bet that would be the first thing they provide.

gbru316

It's not the magnetism you need to worry about these days, it's the electrostatic discharge (ESD). But unless you're shoving a screwdriver into a USB port or opening up the case and stabbing the PCB with said screwdriver, there's no reason to worry about ESD.

scott967

This is the difference of eTap from SRAM mechanical: that "overhang".






The 141 dimension from center BB to center mounting screw is identical to mechanical. The difference is the 22.9 to the overhang. So the braze-on can't extend upwards more than 163.9 on a 50x34 crankset.

scott s.
.

springs

Just curious...was the rub on the outside plate, or on the little tab at the top of the cage that is perpendicular to the side plates? I'd like to know the purpose of that tab.

Danny01

It rubs against the plates. The tabs appear to be for rigidity.

Danny01

Yes. It is the top portion of the braze on hitting the derailleur housing that is the problem. The top the braze on must be filed down. You and I said the same thing, except you used Sram's white papers to show it.

dblackwood72

I guess I got hijacked!

datlas 

Unprecedented.

Danny01

We'd never be so rude. still talking about the etap front derailleur here... keep us updated

nycphotography

The limited vertical clearance is ridiculously easy to fix, just grind a couple mm off the top of the hanger.

From the picture, there's easily 5mm of material you [can] remove, maybe even more.