Chain Length Problem?

[starcitymtb]

I've not had this problem before, but this weekend I was riding at Carvin's Cove and was having a problem with my chain continually popping from my middle ring to the first ring up front when I was descending. I had to constantly drop my shifter into the first ring to have the derailleur pick up the chain and place it back in the middle ring while coming downhill to prepare for the turn. Fine if you are on a nice leisurely ride but not good when you want to get on the peddles to keep your speed on some fast craggy downhill singletrack and hit those berms with any speed.

I am thinking that my chain might be too long but I haven't had any performance issues with my tranny up to this point. I am using a long cage Deore Rear Derailleur, 11-32 8 speed cassette and a specialized three ring aluminum crank on a Kona Dawg (full squish) ride.

Everything shifts well and when I line up my derailleur cage and spindles, everything looks right. Would taking a link or two out help this or hurt my casue? How do downhillers keep their bike chains hooked up in the right gear? Do I have to switch to a short cage tranny?

Any advice or experience is greatly appreciated.

[jabberwocky]

I am thinking that my chain might be too long but I haven't had any performance issues with my tranny up to this point. I am using a long cage Deore Rear Derailleur, 11-32 8 speed cassette and a specialized three ring aluminum crank on a Kona Dawg (full squish) ride.The first thing I would examine is the adjustment on the front derailleur. If it is sitting too far inboard when you are on the middle ring it will give the chain ample room to drop down to the granny when it is bounced up and down.

Next, anything that adds to the chain tension will help a bit with chain droppage. Running the chain as short as possible (just large enough to work on the big-big combo) will help, as will running a medium or short cage derailleur.

How do downhillers keep their bike chains hooked up in the right gear?Single ring up front and a chainguide. Works very well, but impractical for cross country. :)

[starcitymtb]

[QUOTE=jabberwocky]The first thing I would examine is the adjustment on the front derailleur. If it is sitting too far inboard when you are on the middle ring it will give the chain ample room to drop down to the granny when it is bounced up and down.

Next, anything that adds to the chain tension will help a bit with chain droppage. Running the chain as short as possible (just large enough to work on the big-big combo) will help, as will running a medium or short cage derailleur.
[QUOTE]

Thanks Jabber. The Front derailleur was pretty dead on when I checked after the ride. That was what was so perplexing.

Tonight I will see how much room I have on the Big/Big combo. Didn't think of that as a means of measuring. I'm guessing its possible that chain stretch could be the culprit here. All I need is enough length for the chain to climb into that third ring from the first cog, right?

[jabberwocky]

Two things I would check:

One, put the chain on the granny in back, and the middle in front. In this combo the chain should just be brushing the inside plate of the front derailleur (as close as possible without actually hitting it).

Two, put the chain in the biggest chainring you have and the granny in back. In this combo, the derailleur cage should be pulled almost straight forward.

The method I have heard for checking chain length is to remove the chain from the derailleur, and put it on the big-big combo. Pull the chain tight, check where the chain would connect, and then add two links to that.

Total conjecture, but it sounds to me like a front derailleur issue. You said you had to shift down and then reshift back up to get the chain to climb back to the middle ring. If the front derailleur is properly adjusted, the chain should climb back to the middle once you start pedaling without having to do that.

[starcitymtb]

Total conjecture, but it sounds to me like a front derailleur issue. You said you had to shift down and then reshift back up to get the chain to climb back to the middle ring. If the front derailleur is properly adjusted, the chain should climb back to the middle once you start pedaling without having to do that.

Hmmm... true. I will have to revist the issue tonight with the front derailleur.

I copied and printed out your suggestions on the front derailleur adjustment. I will check it tonight and let you know the outcome. That is a much easier fix than having to pop links out. Although I bought a chain breaker last year and never had to use it.

Ohh... maybe a combination of the front derailleur adjustment and chain length? I can't wait to get home and check. Thanks!

[mark w]

Be careful when setting chain length to allow for suspension activated chain growth. If your rear der. cage pivots forward when you squish, you'll need to allow for a little more chain. In big/big your der cage should be at about 45 degrees to the ground.

[FIX_BKS]

Lastly, and in conjunction with all of the other suggestions, there is a screw which comes out of the back of the derailleur and puts pressure on the back of the derailleur hanger when adjusted.

If this screw (looking from the driveside is to the left of the limit screws and parallel to the rear wheel) is not in very far (1/4 of the way or less) screw it in until you notice the derailleur tilt back a little. This will put additional pressure on the chain and take up any excessive "slack" which may be caused by worn out return springs. I would screw in halfway and test it.

Sometimes, if screwed in all the way, it can cause the chain to make less contact with bottom of the cassette and thereby induce a skip, but this is rare and the screw can be backed out a few turns if that happens.

[eloach]

I had that problem with my Giant Trance and took a link out to resolve it. During the suspension cycle the chain would occasionally pop off at the shortest point of the rear cog to BB setup. I checked the chain tension at various points of suspension sag and rebound and found that it was too loose at that point.

I also read that an "inboard chain line" setup can lead to a similar problem, but they were referring to Treks and Fishers in the article I saw. I have to confess I didn't really get what they were talking about. I own a GF Paragon and could not really see it on that bike. I think they meant the chain was angled in towards the BB.

[starcitymtb]

Oasis, so to get the finite tension I want, I can screw down on that rear derailleur screw? I am pressuming that it wont affect my shifting since the screw will be pushing the derailleur back and not side to side.

Mark W, am I to check the forward movement in the big/big combo or is there another ratio that I should check it in? I would have thought on my FS rig that the chain wouldn't move as violently around without any tension as it would on my hardtail.

Eloach, I have a sneaking suspicion that it is a combination of what Jabber said about my front derailleur being set too far in and maybe a link or two. Cable stretch could have caused that in my front derailleur while chain stretch could be another reason.

[starcitymtb]

Jabber, you were right. My front derailleur was not aligned. It was over about a 1/4" or so. It was a quick fix with my barrell adjustment at the shifter. The cable probably needs to be reset but for now the problem is fixed.

When I went Big/Big, there was no more room for another link to come off. While it wasn't overly tight, in the middle and upper rings, the derailleur sat correctly. There was no play in the chain.

However, I did notice that the spring housing on my rear derailleur took a considerable beating this time out against the bottom of my chain stay (nearest the drop out). Maybe that has been going on for some time but I just installed that derailleur in February and it looks like crap already. I can't think that is any good for the derailleur.

Thanks for all your input but Jabberwocky to the rescue. I appreciate it.

[jabberwocky]

Jabber, you were right. My front derailleur was not aligned. It was over about a 1/4" or so. It was a quick fix with my barrell adjustment at the shifter. The cable probably needs to be reset but for now the problem is fixed.Awesome! Lets hear it for lucky guesses. :)

I love it when the fix is easy and doesn't involve spending money. Hopefully that eliminates the chain droppage issues.

[starcitymtb]

Hopefully that eliminates the chain droppage issues.

Yeah I am sure that it will. Its hard to recreate the action of the chain off my curb front so I will try out at Sherando this weekend.

You've done your good deed for the day. Thanks again for your insight.

[FIX_BKS]

Oasis, so to get the finite tension I want, I can screw down on that rear derailleur screw? I am pressuming that it wont affect my shifting since the screw will be pushing the derailleur back and not side to side.

Mark W, am I to check the forward movement in the big/big combo or is there another ratio that I should check it in? I would have thought on my FS rig that the chain wouldn't move as violently around without any tension as it would on my hardtail.

Eloach, I have a sneaking suspicion that it is a combination of what Jabber said about my front derailleur being set too far in and maybe a link or two. Cable stretch could have caused that in my front derailleur while chain stretch could be another reason.
Sorry, didn't get back to my computer until my day job this morning, where I can slack off and talk shop...the irony. But the answer is yes.

I've also seen your post that your derailleur has been smacking the bottom of the chainstay...this (derailleur tension) adjustment can also help with that. You were correct in assuming that this will have no bearing on your lateral shifting adjustments! :)

[starcitymtb]

I've also seen your post that your derailleur has been smacking the bottom of the chainstay...this (derailleur tension) adjustment can also help with that. You were correct in assuming that this will have no bearing on your lateral shifting adjustments! :)

I cranked it down a bit to see if that helps on my next run. I'll let you know. Thanks for the adjustment help. And I only thought I had to set the limits. Hmmphh! ;)