OK, I was too embarrassed to take pictures of my dirty drivetrain.

The mechanical stuff is beyond me. So, I took it in to my absolute favorite shop yesterday. He said the chainring looked straight, they didn't see any issues, but re-adjusted the derailleurs anyway. His best guess is that since it's such a tiny frame, the chain line is just not good, and any cross chaining could be a problem. Basically "i don't know" hmmm... we'll see, i haven't ridden it yet, and won't get a chance to ride outside for a few days, since it snowed 6" over night.

Although I don't know Di2 at all I do know about chain dropping issues.

Small frames aren't any problem with chain lines since the chainstays tend to be the same length as taller frames. For example my 52 cm Cannondale has a 40.5 cm chainstay so the cranks and rear cassette are 40.5 cm apart. This is similar to many frames out there, it's sort of a sweet spot number for regular frames. Any problems with dropping the chain on that bike would probably be related to set up, not the size.

My current Tsunami frames have 39.0 and 39.3 cm chainstays. These are much shorter and the chain line is not as good. I've dropped my chain in sprints in weird gears on bumpy roads (like 53x21 on a bumpy road). It's not fun at all. I found later that I ended up bending a chainring tooth, twisting a (regular, not the Missing Link) link, and even broke my cleat.

If your chain spontaneously drops from the big to the small then typically the cranks need/want to be moved inboard a touch - that would be the best solution, to put the chainrings more inline with the cassette. However I have no suggestions for how to do that with any of the newer cranks.

Huh...yeah, you're right his explanation doesn't make sense. I wish people would just say "I don't know" when they don't know, instead of making stuff up.

I was thinking the same thing about the chain line comment. Unless you're running 650 wheels, the chain stays are most likely the same length as every other size frame of that model. You cannot really make them shorter as they are dictated by wheel diameter.

I had the exact same issue with my Di2 dropping off onto the inner ring, and after a few different tweaks and what not, all the guys at CMS, BCS, and SG all agreed that it was the chainline. Like you nearly identical set up.

Now...what I did do that has fully eliminated the chain drop when cross chained was actually changed my rings out to a Rotor Q Ring. I was using an 7900 DA crank and it simply wouldnt stay on but since changing rings its been flawless. Now Im not saying you need to go to a Q ring or what not but a fresh chainring did it for me. I also added a K-Edge chain catcher just in case for some added assurance.

As you mentioned, moving inboard a bit made all the difference in the world with the dropped chains. Granted I did use a Q ring as a replacemant and it does have less of an offset as the standard DA ring, that seemed to remedy it.

hey--sorry i've been MIA for a bit. just seeing this now.

as shovel said, issues are much easier to diagnose when the parts are in front of you.

here's the full blown list of what i would do if it were my bike. it will take me longer to type it than it would to do it. basically, it's checking everything and doing a fresh install, but with di2 it is pretty easy.

before we start, did you try a different wheel? *shouldn't* matter, but i'd like to rule out any alignment issues.

1) back off all limit screws, front and rear. (this is a front issue, but i'd just do everything because it's quick for me.)
2) back off the set screw on the FD
3) loosen the FD and check the height.
4) adjust the angle of the FD so that the rear is slightly inboard of the front. i like to use the set screw to adjust toe-in. if the set screw isn't making contact with the frame the power of the servo could cause some problems. be sure to use the frame protector.
5) set the RD limit screws. rear low limit needs to be right at the stopping point; high limit should be 1 turn past the stopping point. easiest w/o a chain as you can see the exact point where the cage moves.
6) throw the system into crash recovery mode to reset the RD. it will run through all gears in the rear.
7) install chain, then set FD limits.
8) i'd also check the FD micro adjust. you should never have to use it, but maybe someone did use it and it is not set in the middle of the range? if the problem is still occurring, i might try a click or two outboard, to see if that stops throwing the chain inward.

you could also call shimano directly. they have some VERY knowledgeable support people on their hardgoods line. 800-432-2420. they should help even if you are a consumer. over the years i've gotten some excellent info from reps....one knew their PRO line-up inside and out (he was a trackie and very interested in a stem i was building), and more recently another was a di2 expert (i'd uncovered an issue and was reporting it).

i've known them to take di2 issues very seriously. it's a flagship line for them.

you could do that first, but i'd run through all those steps to make sure things are OK. i'd also update all firmware.

did those shops tell you it was shifting fine when they gave it back to you?

i have seen some issues with di2, but it was on a flexy cervelo. a shop (one inexperienced with di2) did a poor install. cervelo's service team in kona rebuilt the bike for her...but it still had the issue. i found it took very precise positioning of the FD to get it just right, via the above steps.

hope this helps.

di2 is amazing, but any drivetrain problem sucks.

i haven't seen any modern bike with chainlink problems that would cause mis-shifting of this sort. chainlink is usually determined by the crank+spider, not the rings, so i'm surprised to hear it solved an issue--it would be new to me but i'm always learning.

beginning experiment with these rings
http://i.imgur.com/uwoVYtTl.png

first impression from the commute is "weird".

intervals at lunch should provide a better feel.

commuting with the disc?

teton - thanks for the detailed reply. I thought i replied already, but apparently forgot to click "post" and lost it. In any case, I am waiting to see if the last trip to the bike shop fixed anything (no riding outside yet since then) and then will follow up with the bike shop and ask if they did the steps you enumerate, if it's still a problem. While it would take you longer to write than to perform, I'm pretty sure I could screw something up badly along the way. :)

He's that serious about Strava!

it's a clincher, train as you race and all that (getting a feel of wind on that bike is important for me), and I only have one 11s cassette.

also, the stravas, as @mattm says.

nice ... i've got a loaner disc on my TT now (RaceRim). It makes the bike much louder and look way more pro ;)

well played!!!

who here has swapped for an aero road handlebar, any tips/advice regarding cable routing?

also if you've swapped to a 3t aero road bar (Aeronova or Aerotundo), i'd like to learn a bit more about if you needed to change stem length, etc.

I briefly used a Enve Aero Road.. has internal cable routing but tight turns.. ended up using external...then ended up going back to compact road bars. Didn't alter stem length when I tried them.

I'm really looking into the Zipp Vuka Sprint. I did look into the 3t but (this is from memory I could be wrong) they'll typically extend your reach by 2-3 cm, so if you don't want things to change, get a 20mm shorter stem.

i was doing a shakedown ride of a new setup a few days before a race. it was an easy ride....just checking shifting, making sure the disc/tire were all good.....going like 15, 16 mph. i might have even had my TT helmet on as i was playing with the position. she also caught me right as i was winding down.

a woman in my neighborhood saw me and heckled me --something about needing to go faster with a full TT setup. i laughed--she was dead-on.

fast forward a couple years and someone flags me down. it's some woman who has seen me riding a bunch and has bike questions. turns out she's some sort of competitive triathlete (they all seem to be "competitive" from a personality perspective, i guess, but most are "completitors" :)) and needs guidance on bikes & positioning.

i hadn't thought about the situation in years but i immediately recognized the voice and remind her of that incident. she apologized, but i told her it was funny and dead-on. i would have heckled me, for sure.

even though i have a clincher dis, i don't train on it, and i'll never use a TT helmet for training....unless i am specifically testing something, and even then i'll keep it under the radar from my wife. she is embarrassed -- for herself and for me -- by that stuff. we even had a local run & ride (5k run + 15k bike), and she didn't want me to wear the TT helmet. but everyone who owns a TT bike is on it & full aero. was fun to try to beat the TTers who are relaying it after i ran 5k. NOT easy to bike at threshold after running for 20'. ouch!

/cool story.

I was looking into AeroNovas as well. On WW they claim it ends up being basically the same as the Ergo Nova (somehow the measurements are misleading, apparently).

Also, check out shifter compatibility - as I understand it, the internal routing does not work with mechanical or earlier versions of Di2.

I do dress rehearsals on the TT bike quite often - wheels, skin suit helmet and etc. It is different and feels different to be in race configuration and the bike handles differently. I guess some are more serious than others about performance.

I put on aerofly bars. Cable routing was a breeze. Tip: use a j-bend spoke to fish the cable through.

thanks for the tip. though i may just pay the LBS to do this...
yeah, that's the thing. they are measuring reach from the back of the airfoil as opposed to the middle of the section, so apparently it's a 10 mm difference, i think. i'll be using the Aerotundos if i do end up going with 3t
people say going with a shorter stem changes steering, but that's usually when one is not also extending reach of handlebar, right? can anyone shed some light on this?
got it; thanks

what's the trick to truing a wheel with bladed spokes?

i was trying to hold the spoke with pliers, but the part below was still twisting.. lube maybe?

zipp 404 w/ sapim? X-rays or something like that.

I use a Mavic bladed spoke holder that came with a set of wheels I bought a long time ago. Park makes something similar. The trick is to apply apposing forces, overshoot the true point, then back off and straighten.

I use a Park Bladed SPoke Holder (BSH-4):

http://www.parktool.com/uploads/thum...a0_430x390.jpg

I hold the spoke as close to the nipple as possible, else the spoke twists. The BSH-4 works best if you're turning the nipple from the rim's tire side, not the regular spoke nipple side.

I recently retensioned an Ardennes type rim (Bastogne wheel) using a socket nipple driver and the BSH-4. The rim has exposed spoke nipples but I realize that the park spoke wrench forced me to move the BSH-4 too far up the spoke. I reverted to the socket nipple driver.

Too mechanical.... he needs an App.