Trek Pilot 5.0 chain drop
 

I'm on my 2nd frame due to rear triangle miss alignment and resulting in the chain dropping off the granny gear when I down shift. This continues to happen with my new frame. No real success at preventing this by derailer adjustment (Shimano 105 triple), but it does happen less frequently if the derailer is just barely rubbing chain in my lowest gears (30/28). It will drop off at least once every ride and the carbon shell is really taking a beating (it won't last long at this rate). No way to put a chain keeper on that I can see, so here's my question. Will another front derailer like a deore work better than the 105 and prevent this?
No one has checked the chain line on the new frame yet, as I havn't complained, but I can't believe I could get a second misaligned frame!!

I'm not a bike mechanic, but maybe you've got something else working there, like too much chain. I guess you're using a 9-sd freewheel that came with the bike?

Maybe the rear dr is bent. Otherwise, I'm surprised that the chain will go off the 30T ring when the front dr's stop is set correctly, or that it would be a frame issue if it did.

If its a 10spd setup, check that the spacers on the crank spindle are installed properly. I believe you have like a 2mm spacer on one side and a 3mm spacer on the other, or something to that effect. Long story short, many bikes come from the factory with two spacers installed on the drive side, but the crank must be removed and the beveled spacer moved to the non-drive side of the spindle as I recall. Not sure if thats for all Shimano 10spd triples or not, however.

As Seely suggested, check the spacers (depending on your crank). Measure your chainline and see how it is.
Deore derailleur is a no-go for your setup.

It's a 9spd setup. I will check the chain line and the spacers this afternoon. Thanks for the tip.

Is it the new outboard bearing 105 crankset?

By the looks of things on Trek's site, spacers are not going to be part of your bb setup. It looks like the older Bontrager version of the Truvativ Elita cranks.

If its a Truvativ crankset, many of them were recalled for issues with dropping chains. I have a 10spd Bontrager Racelite on my bike and it does drop the chain much more frequently than my 9spd Shimano ever did, for whatever reason.

Yes, it's a Bontrager Race Lite, outboard bearings, giga-pipe etc.

Well, it's a Bontrager Race Lite, 9spd. Not sure about the Truvativ part. I figured Bontrager was an in house design? Small world. I think I'll contact Bontrager and see what they have to say!

Its actually a 10spd crankset if its the Gigapipe... definately a Truvativ crank. I generally like mine, but I also have the updated rings.

Yes, Giga X Pipe in small letters on drive side. I checked alignment of frame and it's within one millimeter on each side. Chainline looks ok too. Updated rings? Tell me more. I contacted Trek today and all they said was to have the dealer call their tech support line and they would take care of it! Been there, done that.

I don't know much about it... I just know that they were having a problem because the Ultegra level rings (Racelite) were spec'd to Shimano Dura-Ace standards supposedly, and they didn't work quite right. Lots of issues with dropped chains with all levels of Truvativ cranks in the past 2 years, so I personally think they are full of **** and its their problem, not Shimano's. However, they did send my boss 4 or 5 sets of chainrings and two free cranks (one of which is on my Synapse) after his chain went off the outside of the big ring during a 35mph sprint. The rings my crank came with were black, the new ones are a gold/champagne colour... thats about all I know as I just build/fix/sell bikes, I don't handle the warranty.

Thanks a lot for the info. I was really beginning to wonder, what the %&* is going on. I have the black chainrings as well. I guess I'll see what the Trek people have to say tomorrow. Thanks again.

Yeah no problem, I would think a bike as new as yours would have the problem fixed, but you never know.