chain dropping

This is happening on my 'cross bike/commuter. It's set up with a single chain ring (I think a 39), and a 10 speed cassette. I rode it all winter with studded tires, and didn't drop the chain once. Now I have thinner tires, and I've been dropping it often, twice tonight. It always happens shifting while descending, and the chain falls off the chain ring, to the outside, and gets caught on the pedal (there's no front derailleur). So, my thought is to put a larger chain ring on while I have on the thinner tires. I have plenty of gears for climbing, so I'm not worried about that. Do you think a larger chain ring might solve the dropped chain issue?

I don't really want to put a chain guard on it, but I know that's an option. If that's the best one, let me know, and I'll do that.

perhaps could your chain just be stretched from the winter ridiing. I know the last time i took my bike in because I was dropping the chain, they did some kind of measure test on the chain and then replaced it (about a $35 chg as I remember). problem solved.

1+ on callmej the problem maybe with the chain and or chainring. Look for a bent chain link on your chain, have your chain measured and you front chainring looked at. ;)

Is your derailleur clean and lubed? If it's cruddy or dry after the winter, it could be slow to take up the slack when you upshift.

I suppose RD springs wear out over time, too ... I've never known that to happen, but springs generally lose their springiness, so if yours has a lot of miles on it, I'd think that would be a possibility, too.

I haven't cleaned the drive train well (okay, fessing up, I've hardly touched it :o). It's cruddy. I'll also have my lbs measure the chain.

The same thing was happening to me a lot last year in the later part of the year. Each time I dropped the chair it was on a downhill while shifting, I had it checked out at my LBS and they could not find anything wrong with it, not the derauiler, the chain itself or anything. Most of the time I was able to get it back on but once it got so fouled up that I had to walk the bike back to my car when I was out about 2 miles into the trail. I was not a happy camper.

At the end of the season last year I had a complete tune up and had one of the wheels trued up. So far I've dropped my chain once this year. I don't know what to say. I think it might be me. I've been more consience of shifting on downhills and have not dropped it again yet. Knock on wood, now I'll probably drop it tomorrow because I'm planning a longish ride :eek:

I had a similar problem with my bike. The LBS didn't measure my chain but they replaced it and the problem was solved. Seems like a pretty simple (and cheap) thing to do to start eliminating possibilities for the root of the problem. I didn't even know you were supposed to be cleaning the chain. Now I use a degreaser every other week or so (it doesn't rain much now since the drought but there's plenty of dust kicked up!) and I've had a lot more luck getting the chain to last longer and I don't have the dropping problem anymore when I apply more power.

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Originally Posted by Bike Writer

Each time I dropped the chair it was on a downhill while shifting, I had it checked out at my LBS and they could not find anything wrong with it, not the derauiler, the chain itself or anything.

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There might not be anything "wrong" with the parts. This can be a characteristic of 1xN drivetrains. When shifting to a smaller cassette cog, the shift can happen suddenly and fast. This may cause a sideways wave in the chain. The front part of chain was still angled for the old cog while the back was bending over to the new cog. I think there's also an up and down wave from shifting into the smaller gear. These waves can be enough to throw the chain off the chainring when there's no derailleur to block them.

My commute bike has a single chainring up front. It came with a plastic guard on the outside of the chainring. When I changed to a smaller chainring, I installed metal guards on both sides. The guards are essentially toothless chainrings.

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Originally Posted by laura*

There might not be anything "wrong" with the parts. This can be a characteristic of 1xN drivetrains.

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Yes, this is true. I know it's part of the problem, for sure. I am thinking about the guards, but I'm still looking for an alternative before I go that route. It may be the best thing, though.

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Originally Posted by laura*

There might not be anything "wrong" with the parts. This can be a characteristic of 1xN drivetrains. When shifting to a smaller cassette cog, the shift can happen suddenly and fast. This may cause a sideways wave in the chain. The front part of chain was still angled for the old cog while the back was bending over to the new cog. I think there's also an up and down wave from shifting into the smaller gear. These waves can be enough to throw the chain off the chainring when there's no derailleur to block them.

My commute bike has a single chainring up front. It came with a plastic guard on the outside of the chainring. When I changed to a smaller chainring, I installed metal guards on both sides. The guards are essentially toothless chainrings.

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1xN drivetrains? Does that mean only one chainring up front? I think that's what you mean, I have a chain guard and that does not prevent the chain from hopping off and also gets in the way when you are trying to fix a dropped chain. sigh.

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Originally Posted by laura*

There might not be anything "wrong" with the parts. This can be a characteristic of 1xN drivetrains. When shifting to a smaller cassette cog, the shift can happen suddenly and fast. This may cause a sideways wave in the chain.

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That's interesting, I'd think that with one chainring in front you'd be spared a chain ever falling off again. I never thought that the front derailleur would work as a chain guard. But 10 speed in back is a pretty wide spread for the chain to handle too. Park Tool (I think?) has a very neat and cheap little gadget called a chain checker btw, which tells you in a second whether your chain is worn. I love mine, and have recommended it as basic maintenance gear to many people.
Also the rear derailleur could be a little slow in taking up the slack if you've ridden in winter and it's a bit draggy, so that you have an instant where the chain has a shorter circle to travel but hasn't been pulled tight yet. Just an idea.

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Originally Posted by lph

That's interesting, I'd think that with one chainring in front you'd be spared a chain ever falling off again.

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That's what I thought too! Then I started researching what I needed to change the chainring on my commuter bike. The OEM guard of course wasn't suitable.

1x9 (and other cassette sizes) gearing is apparently popular on cyclocross bikes. Those riders "talk" a lot about needing guards.

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Originally Posted by laura*

That's what I thought too! Then I started researching what I needed to change the chainring on my commuter bike. The OEM guard of course wasn't suitable.

1x9 (and other cassette sizes) gearing is apparently popular on cyclocross bikes. Those riders "talk" a lot about needing guards.

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Ah, I wish I had asked this before I decided on 10 speed. I also thought I'd never drop a chain on this bike, due to the single ring. Who knew?!

Thanks for all the input.

There are lots of possiblities that could cause this, as many have mentioned already. FYI: a chain does NOT stretch, but the bushings/sideplates do wear which give the indication that a chain has stretched. AS the chain wears, it tends to get sloppy shifting and makes derailleurs work a bit harder. IF your rear derailleur is starting to wear as Oak mentioned, the spring will not have the ability to shift as easily and will tend to "hang up" a bit more...often times getting stick in a couple of positions. In the late 80's/early 90's we used to be able to buy and replace springs for customers, unfortunately haven't been able to offer that service for quite some time. There is a quick test that you can perform yourself to check the rear derailleur, although you will need to put the bike in a stand or suspend it somehow. Once you have the bike supported, place the chain on the hardest(smallest) gear in the back. Pedal the bike by hand, and push the rear derailleur with your other hand so that the chain is on the easiest cog in the back(biggest). Once on the biggest cog, let it go and the derailleur should snap instantly back down to your hardest cog. If it tends to hang up abit, then that's an indication that you need to replace the derailleur as the spring is indeed wearing out.

Now of course, this is meant for bikes that have the proper cable tension, derailleurs/dropouts are straight and are set up correctly.

Good luck :p


http://chasecyclery.blogspot.com

I cleaned the derailleur, and it wasn't that bad, just a little crud on the jockey pulleys, but maybe that was part of the problem. I found this article on single chainrings, with info on guards, so I may end up going that route.

http://www.bikeman.com/content/view/78/115/