chain that jumps off

[carpe_simius]

hey y'all,

today i was riding my bike and just messing around.
twice i jumped it off from grass to pavement, no more than 1ft-1ft 1/2 and the chain jumped off from the mid crank.

the 1st time it jumped all the off and teh 2nd it jumped to the lowest 1st crank.

what can i do?

im gonna take it to my lbs but i thought id ask y'all first.

[Matt D]

It could be a lot of things.

For instance, your front derailleur may not be adjusted properly or your chain may be too long.

BTW, you have a SET of cranks, a left arm and a right arm connected by the bottom bracket. The right crank arm is what the CHAINRINGS ride on. You probably have 3 chainrings, but you can have 1-3 depending on your setup.

[Repack]

For lack of a better explanation, it "Hoola-hoops" its way off. Bottom sinks down, the slack swings around to rings, its off. Try hitting drops in bigger rings or get rid of the big ring and tighten the chain. If its not full suspension, try dropping in gear combo's closer to big-big.

[carpe_simius]

thanx. ill try it in higher gears. but is that normal?
to me it doesn't seem like it should happen.

i dunno

[greasey monkey]

This was happening to me and it ended up being the rear derailer pivots were gummed up and rusted and not keeping good tension on the chain. I pulled the rear derailer apart cleaned and regreased the pivots and it works like a charm.

[Repack]

Originally posted by carpe_simius
thanx. ill try it in higher gears. but is that normal?
to me it doesn't seem like it should happen.

i dunno
It is completely normal. The derr's full time job is to keep tension on the chain. It is only shifting maybe 1% of the time. The chain flopping up and down puts a lot of pressure on the derr. Think about picking up a loose end of rope up off the ground and giving it a good shake. You see the "bulge" travel down the rope. Pretty much the same as what is happening to you chain, except that bulge is a slack spot, and when that spot get to the rings, it causes the chain to jump. A few years ago I ditched the big ring, shortened my chain, and have had far fewer lost chain issues. Maybe an e13 DRS would be a good buy for you. They work well enough to be used for 4x.