ArgoMan

Hi all. Went for a ride with my son this morning. We hit a hill (more like an exaggerated grade) and his chain came off the large chainring (2x10, Tiagra). It's a new set up and the groupo was installed by my LBS. We re-attached the chain and then it happened again on the next ascent! What are some of the common issues that may be causing this? Thank you!

Iride01 

Trying to shift was my thought too. Especially if he is waiting till his cadence is already too low. And also the possibility that shifts aren't getting completed before pedaling is stopped for what ever reason, be it stopping pedaling and coasting briefly for clearance to traffic ahead or stopping just because pedaling became too hard because going to the next easier gear was too late a decision.

Eric F 

Also look for damaged/twisted teeth on the chainring, as well as damaged/twisted chain links.

ArgoMan

Thanks, to be honest he was riding an old school bike with the the old 80's Suntour-type shift levers that didn't click when you switched gears. The new Tiagra setup is totally new to him. He also has some real difficulty thinking simple things through. So maybe he's just not shifting correctly, if that's somehow possible. I really don't know what "cross chained" means. The chain itself is brand spanking new.

Sy Reene

Is the chain falling off to the outside or inside of the big chainring?

Eric F 

Cross-chained is...
1. Being in the small cog at the rear and the small chainring in the front.
2. Being in the large cog at the rear and the large chainring in the front.

It is generally good practice to avoid both of these conditions. Although bike chains have some tolerance for lateral flexibility, it's pretty limited, and everything works best in a straighter line between chainring and cog. These scenarios put the chain at the most extreme angles, and it can cause issues. Because chains, chainrings, and cogs are designed for shifting from lateral pressure by a derailleur, big-big or small-small can cause an unwanted shift just from the lateral pressure caused by the angled chain line. It might also be at the limits of the rear derailleur's capacity, which is also not recommended.

rsbob 

If the chain is being thrown off the outside of the big ring, your derailleur needs to be adjusted. This is a DIY. Watch this: https://www.parktool.com/en-us/blog/...eur-adjustment

Kontact

You should ride it to see if you can duplicate the problem, then take it back to the shop that assembled it.

79pmooney

Tell us all you can about the shifts where the chain falls off. What gear were you starting in? Where did the chain go? Off the outside or between the chainrings? The more we know, the better we can help. (Maybe you need to take the bike out and see if you can duplicate the events.) Any bike shop will love the same information. What happens on the road cannot always be duplicated on a stand.

Homebrew01

I would think he was shifting to the smaller front chainring to go up the hill, and it overshifted onto the frame bottom bracket. Correct ?
It may just need a simple adjustment of the 'L' screw to prevent the front derailleur from moving inboard quite as much.

eduskator

Where? Between the small chainring and the frame or between the bigger chainring and the crank arm?

If it's dropping between the frame and the small chainring when you change gear from the big to the small ring to climb a hill, it's most likely your low limit screw that isn't properly adjusted (your chain gets thrown too far inward). Bring it back to your LBS that installed it; they will adjust it free of charge.

Rolling15

I had the same problem on a new bike that was assembled by my LBS. Changing gears under tension would sometimes cause the chain to come off. After trying various adjustments to no avail, the head mechanic took a look and removed a link from the chain. It seems that when they assembled the bike, they allowed for too many links between the chain ring and the rear cluster. It worked like a charm. I've never had the chain fall off since.

WaveyGravey

I am having the same issue with my Bianchi 1885.
Chain doesn't fall off during a ride. When rolling in reverse to store or such as this. I believe it may be too loose a chain.