front chainring question

[teperilloux]

hey y'all, newbie posting a question here:

I have a Trek 5200 and whenever I pound hard up a hill, the chain comes completely off the front chainring when I'm in a low gear in back.

It doesn't come off when I'm in high gear in back; so during normal cruising it's not a problem.

There's also a creak per pedal revolution that sounds like it's coming from the front chainring, but no noise from the rear.

It just started suddenly, so would this be a symptom of a stretched chain and time for a new one? Would a partially broken link cause something like this? I couldn't find anything broken upon chain inspection. Any help would be appreciated. thanks, Tom

 

[drewjc]

teperilloux, if u r using the large chainring and the largest sprocket (???) at the same time, and pounding the pedals there is quite often too much sideways force on the chain to hold it's position on both of these gears. (Look at the chain angle from above and see for yourself) Derailleurs aren't designed to stop this from happening, as it is only a problem in more modern bikes with 8+ rear sprockets creating a very wide cassette.

The sound coming from the front of your drivetrain sounds like a bottom bracket creak to me, but it is always hard to tell as sounds resonate through the tubing and often don't originate from the point of the actual sound (you may need to grease the thread on the bottom bracket cups or apply thread tape). If this isnt the problem then maybe your chainring pins are loose and need tightening. Hope that helps.

 

[teperilloux]

thank you for the reply... What worries me is it happened suddenly. I've ridden the bike fine for hundreds of miles, all of a sudden I can't keep the front chain ring on. Although it looks fine, I'm going to put a new chain on. Any other suggestions? And help would be appreciated. thx, Tom