Mountain Biking - Chain skipping off.

I have a Giant NRS, When I hit somthing hard, like riding along and wheelieing up to a log, hitting the rear wheel on the log and trying to crank over at the same time, the chain tends to skip off. Or even more annoying, riding along flat ground and having a few feet of VERY steep rock, I pull up, throw my body forward and power down on the cranks, when the rear wheel hits the rock, the chain skips off the front. This usualy always happens in a mid range gear, but im almost always in a mid range gear in these sort of situations. So my question is why would this happen?

Before you respond with, your chain is stretched, your middle ring is worn out, your cassette needs to be replaced. I just replaced all three of those things thinking that could be the problem. Also Before you tell me the bike is probably miss tuned and its skipping because the derailur is a little between gears, while my tuneing isnt perfect, its tuned pretty well, and the front, where it skipps off, shifts perfectly.

My theary is that when the rear suspnsion compresses a lot, as in when it hits a log at speed, or a sudden grade change like a steep rock face, my chain line is changing length, shorter combined with cranking could hop the chain off, longer with cranking could just be too much tork for it to handle. Is this a possible answer? and if so it seems like somthing I cant do anything about.

Thoughts, coments, sugestions or just poking fun at me are all welcome.

Your shifter cable housing is probably either too long or routed incorrectly. When the suspension compresses, it shortens the length between the derailleur and the shifter, thus decreasing the length of cable needed to reach the derailleur. Take the bike to a shop and ask them to assess (sp?) the length of your housing. Ask them if it needs to be shorter or longer.

Another possible problem is that your lower limit screw is not properly set. This won't affect shifitng, but it limits how far the chain can move towards the inside of the lower chainring. If this is the case, look in your manual to see how to properly adjust the lower limit screw.

If either of these things don't work, ask a shop or call Giant.

As for the cable housing... Im going to take a look at it when I leave work, however changes in the cable housing length shouldnt have a large effect unless the cable is being stretched by a housing that is too short. Also this problem would cause the bike to downshift when the cable is pulled too tight, AKA when the suspension is fully extended, and cause the bike to upshift when the suspension is compressed. I do not run into either of these problems. My shifting on the casette is good.

As for the low end stop on the front derailur... this happens to me in the middle ring, not the small ring, so the stop should have no effect, however going on that theory, if the derailur were pusshing slightly on the chain it could push it to the next lower gear. However the derailur is not touching the chain while riding along in the middle ring.

The chain is actually loosening around the middle ring so that the cranks can rotate under the chain. This is what is causing the chain to fall, somtimes it stays over the chainring and if I stop pedaling and then start again the chain is retained. I dont mean to bash your recomendations, they were good ones, its just that I have been working on this for a while and still cant fix it so I know a lot of the problems it could be but isnt.

As for the cable housing... Im going to take a look at it when I leave work, however changes in the cable housing length shouldnt have a large effect unless the cable is being stretched by a housing that is too short. Also this problem would cause the bike to downshift when the cable is pulled too tight, AKA when the suspension is fully extended, and cause the bike to upshift when the suspension is compressed. I do not run into either of these problems. My shifting on the casette is good.

As for the low end stop on the front derailur... this happens to me in the middle ring, not the small ring, so the stop should have no effect, however going on that theory, if the derailur were pusshing slightly on the chain it could push it to the next lower gear. However the derailur is not touching the chain while riding along in the middle ring.

The chain is actually loosening around the middle ring so that the cranks can rotate under the chain. This is what is causing the chain to fall, somtimes it stays over the chainring and if I stop pedaling and then start again the chain is retained. I dont mean to bash your recomendations, they were good ones, its just that I have been working on this for a while and still cant fix it so I know a lot of the problems it could be but isnt.


Throw it out a window...





































































































































or into a shop.