Chain falls off chainring...why?
 

I have a Giant Aluxx frame with a Campy Centaur 10sp rear wheel and a 30-year-old Huret Jubilee rear derailler. No front shifter and only a 53-tooth Shimano 600 chainring. I use a bar-end to shift the rear. Rear cogs are 12-28 approx.

Very often when I shift the chain falls off the front ring. Either insider or outside. Going fast or slow. Shifting quick or gently. No particular cog. I can't figure it out.

I've tried shortening the chain and also max-tensioning the rear derailler. No improvement.

Any ideas for a simple cure other than installing a front derailler or some sort of chain-keeper?

(I don't notice that my chain hits my front derailler on my other bikes, or that they're trying to derail but are prevented by something. So it's hard to imagine that a front der would be the wonder cure for my problem. Maybe it's my primitive 1970's rear derailler

Those are the simple ideas. Derailling of the chain from a single chainring used with a multi-speed rear is a frequently reported problem and the usual preventative is a fixed-in-place front derailleur or an outer chain guard and an inner chain watcher.

The problem may be exacerbated by your chainring. If it has the shaped teeth, ramps and other modern shifting enhancements it will make the situation worse. A "flat" old style or track, fixed gear or single speed chainring might reduce the spilling tendency.

Plain Jane rings are commonly available. http://www.loosescrews.com/index.cgi...d=741065212454
I ran 7- and then 8-speed single ring setups for several years and dumped the chain only occasionally.

Surly also sells plain, flat stainless steel chainrings intended for fixed and single speed applications so they have no shift-improving features. Their only downside for your use is that the largest they come in is 50T. Look here: http://surlybikes.com/parts/stainless_steel_chainrings/

Thanks, folks. I think you're on the right track with this "ramps" stuff and a flat ring solution. But it's my flatland go-fast bike so it'll probably be hard or pricey to find a flat 53t. I suppose I'll let go a bit of weenyism and just add that front der. Or maybe I'll fabricate a keeper somehow. ...Any idea about a simple, easy to make keeper?

Use a track chainring with full-profile teeth.

I'm still messing with my single ring concept. I was going to get a track ring but people tell me they are thicker and meant for a thicker chain. True? Will they work OK with regular chain? Hmmm, I'm using a 10sp cogset back there.

It seems to still fall off occasionally and I'm almost always in a middle cog. I was wondering if it might be related to my using an old Jubilee rear derailer. It certainly wasn't doing much with chain tensioning. So I've installed a newer derailer -- it's long-cage even. I re-added some chain, too. I haven't ridden enough to know if it's a fix or not. Well, it has dropped ONCE with this new setup but that was soon after I took it out of the car so who knows. It was dropping most when doing intense riding at my max output. (Argh.) But it didn't the last time. ...Just once right at the start.

Maybe there are flat non-track rings? I'm guessing that's what the Surlys are.

Chains drop when they try to "shift" off the side of the chainring. This always happens where the chain is moving onto the chainring. The RD sits after the chain has already come off the other side of the chainring, and will have nothing to do with chain drop. Even the tension it provides is mostly to keep it on the rear cogs, not the chainrings. You pedaling provides the tension for that. If it's providing no tension at all, some slack might appear between the cogs and chainring when coasting or backpedaling, but that doesn't sound like when your chain is dropping.

I had the same problem when I went 1x7. The Surly chainring solved it. But if you really want 10 in the rear, I don't know that you have a simple solution because I doubt that chain would mesh with this ring. Ask Surly, they're good about responding to email.

I agree. Or, that's how it SEEMS. Bikes are mysterious. They're scientific but their science is only partly known. I'm not exactly sure when my chain derails. Maybe it's from a micro-pause resulting in a tiny wave of chain approaching the crank. Maybe the rear der has some effect on the formation of such chain-waves. Who knows, not me! : ) I will try anything, firstly with what I have on hand. I'll try a couple more rides to see what happens. If it keeps derailing then I will finally throw in the towel and try to find a flat ring that will fit my chain. Whew!

I have a decent supply of SunTour Spb Pro rings (130mm BCD)without shift gates. I also have some others that would be less expensive.

The other thing that would help is to shop chains carefully looking for ones with more bellmouth or chamfer on the insider of the inside plates. The chain gets picked and centered by the tips pf the teeth sliding between the inner plates, so the wider the entry point is, the better. The inner place chamfer varies significantly among chain brands, and isn't any kind of listed spec. so eyeball various chains to find the best candidate.

All this won't necessarily solve the problem, though it should help. While the front derailleur doesn't keep a chain on after shifting, it does help redirect a chain that's about to fall off after a bump or jolt.

To understand your problem, imagine trying to free a garden hose past a rock it's snagged on. You flick the end, sending a wave down the hose hoping to flip it over the rock. Whenever you shift, the chain's movement at the cassette sends the same type of wave down the chain, and that can move it far enough to catch the tip of a tooth and climb up and over. You can prevent this with a well timed tiny pause in pedaling, but if you ride bumpy roads, or shift frequently you're probably going to want to add some kind of anti-derail feature, since today's chains are too narrow to stay on reliably with a 1x9 or 1x10 setup.

There are two single speed chain widths- 1/8" and 3/32". Multispeed bikes use a 3/32" chain [almost] exclusively. Yes, even modern 10 speed cassettes- as more cogs have been crammed into cassettes, the overall width of the chain has decreased, but the width of the holes of the chain has remained constant at 3/32".

Do a search for a 3/32" track chainring and you'll be good to go.

If it's truly mostly flat I would think you'd hardly miss the 2% reduction in high gear that would result from going to a much more available 52 tooth.

I had a similar problem for a while. Had about 9000 miles on the chainring. Shop looked at it and said the teeth were so work they looked like shark teeth. After replacing the chainring, it stopped immediately.

Track chainring won't work, they are 1/8" wide and need to use a 1/8" chain. That's about 2x as wide between the inside plates as a 10-spd chain.

I had this chain-drop issue a long time ago when I started riding single-speeds. I managed to resolve it over the course of a year with lots of one-legged riding exercises and 3-5 hours of riding rollers per week. Once I was able to ride one-legged on rollers, I never dropped a chain on the single-speed again.

There are plenty of 3/32" single speed chainrings out there for you to choose from, but those designated "track" are usually 1/8" and not for you. As I posted earlier, I have a decent selection at various qualities and prices, so feel free to PM me with the size you want.

I Run a big single ring on my small wheel Bike Friday.. its a 53t..
BiFri has big chain/trouser-guards for the outside [130bcd]
I added a 'chain minder' on the inside ..
chain stays in place , has stops to keep it there, on either side.

QBP stocks the 3/32 thick larger, alloy, single speed chainrings..