using chainring/large cog as tensioner?
 

i've seen this being done by either somebody here or someone on MTBR.com. they put a ring/cog in the chain near the rear cog to tension. i did this to my bike (although i could have just took out a link because i got horiz drops, but that meant readjusting the vbrakes) and it seemed to hold pretty well. question is, is this an effective solution (even for vert drops) and does the ring/cog fall out (my chainline is pretty near perfect)?

That was me, it never fell out.

http://webspace4me.net/~anthony/singletranny2.jpg

Are you doing this on a fixed gear or ss freewheel setup? To think I just spent about 50 bucks to put a Surly Singleator on my ss freewheel bike when I could have just stuck a cog in there for free! Bet it gets some funny looks, too, eh?

It looks like the only thing holding it in place is the tension between the two chain lengths. If this is the case, I can't imagine that it will stay in place. One good bump and it will come dislodged.

Is this a serious setup, or are joking?

'Tis a serious set up. I ran it for three years with nary a problem.

And it is good and bumpy around here.

RainmanP, t'was a freewheel setup.

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i am doing that now too. thing is my chain always was a bit slack, and on the bumps it would fall out when i pedal. it actually works quite well though. and i dont know about you, but i think it looks kind of neat =]. imagine putting an anodized chainring or cog haha.

OK tried it on a different bike and it ran flawlessly for about an hour (lots of bumps and rocks) it didn't fall out. then out of nowhere i was going down a paved road and it falls out, into my rear wheel, snaps some spokes, derails the chain. just had that wheel re-built too %@#$!!! this was a couple days ago, i threw on an old rear der. worked well during today's ride. rounded nipples caused wheel not to stay true though.

I say go for a chainring they work pretty well and arent too pricy. Thats actually the next step for me on my bike because the chain is starting to loosen up a bit.

Apparently it's not an uncommon solution on tandems in the chain between the captain's and stoker's cranks. It's called a phantom chainring. Here's some more info:

http://www.mtbr.com/faq/ssfaq.shtml

In theory if it's done right, it shoud stay put (though you'll lose some mechanical effeciency). You'll want it to be tight enough that you can't get the chain to lift off the teeth of the phantom ring at all.

My friend has a tall bike that uses this method. I think its an awesome way to get chain tension. It looks really cool and gets alot of looks. Anyone else here into tallbikes?

I see a few around, but don't have any myself. got any pics?

You should also probably use a ring with "more" teeth than one with "less" (exactly what more nad less are, I don't know). You want to limit the angular separation between teeth so that you can always be sure that you have good tooth engagement in the chain, to hold the ring in place. At the same time, more teeth = more friction. It could also have some lateral sway that would annoying.

Sadly, no. I personally think tallbikes are rad as hell. I've got this idea of making a tall bike with a triple chain. Using a multicog freewheel and 2 sets of 2 ring cranks(one on the bottom frame without arms, one on the top to pedal) and making a triangle with a chain from one back cog to one ring on the bottom crank, then a chain from the other ring on the bottom crank to a ring on the top crank, then a chain from the other top ring, to another cog on the back. You would lose a ton of pedaling energy, but it would look damn cool, considering you could weld the frame straight enough to keep chain tension. I've never seen it done.

That does look cool, I wonder if you could use consecutive "phamtom rings on a tall bike? for instance
one smaller, about a foot further one larger, then another foot further one the same size as the first?