[tammy]

OK, I'm doing this 24 hour race in a couple of weeks on the singlespeed. However, I would like to have 2 bikes there, so I have at least one as a backup bike. The only option I have is converting my 4.75" trail bike.

Right now, we're using the rear derailleur as a chain tensioner, and it seems to be working so far (pretty much the same way it does with a full cogset). However, we tried it with a new chain on the old chainring/old single cog - and currently it is making a nasty noise (although not skipping or dropping). So we're gonna try switching back to the old chain that I was using with that chainring/cog and see if that quietens it down. Hopefully the noise is a simple reaction to a new chain with an old chainring/cog, and putting the old chain back on will solve that.

Granted, I have only ridden it around the yard, and haven't tried it on the trail yet, but Psycle-On put hard torque on it and it showed no attempt to skip or drop the chain, so hopefully the derailleur will hold the tension. I'm not mechanically inclined, but I don't see why that wouldn't work as long as the derailleur is adjusted correctly for the single cog, since it works with a full cogset.

Are we just terribly wrong here? Is there any reason why this would or would not work? Has anyone converted an F/S to SS before? Any advice or suggestions would be greatly appreciated. Thanks!

 

[Echo]

I think the real thing that is terribly wrong here is that you are doing a 24 hour race on a single speed

(j/k, congrats )

 

[BikeGeek]

I never did a FS to SS conversion but I think I know the noise you're talking about. While it could be as simple as new chain on worn cogs, I think it's chainline. It's that noise where it sounds like it's trying to shift, right?

It took me about a week of everyday adjustments to get my rear and front cogs lined up and derailleur-tensioner set properly. I had to use a combination of cassette spacers, including the 1mm ones, to get it right. Everything was running nice and smooth until I changed the front ring. My problem? I was using a square taper BB and when I put the crank with new ring back on, I didn't get the crank tightened to the exact position it was before the new ring.

I assume you set your derailleur-tensioner up using a piece of shifter or brake cable to keep it in place. Did you leave the barrel adjuster on so you can do tiny left and right adjustments of the derailleur?

 

[Squeak]

Originally posted by BikeGeek
..... Everything was running nice and smooth until I changed the front ring. My problem? I was using a square taper BB and when I put the crank with new ring back on, I didn't get the crank tightened to the exact position it was before the new ring.

Did the exact same thing last week. Had problems with chainline.

 

[SwisSlesS]

Putting the old chain back on will fix the problem, guaranteed. Whenever you replace the chain or rear cog, you need to replace it's mate (replace chain, replace cog; replace cog, replace chain). These two pieces wear together, so if you just replace one, the two pieces will not line up perfectly which will give you nasty noises, and in some cases, skipping and chain dropping.

 

[bomberz1qr20]

Originally posted by swiss_less
Putting the old chain back on will fix the problem, guaranteed. Whenever you replace the chain or rear cog, you need to replace it's mate (replace chain, replace cog; replace cog, replace chain). These two pieces wear together, so if you just replace one, the two pieces will not line up perfectly which will give you nasty noises, and in some cases, skipping and chain dropping.

Let me elaborate on this a bit.
Change your chain often. When the chain stretches, it wears the spaces in between the teeth on the cassette, widening them to allow for the longer distance in between each link in the chain. Get it?
So when you pop a new unstretched chain on there the widened teeth spaces allow it to slip under hard torque. This is especially true on smaller cogs with less teeth to grip.

If you change the chain before it's too stretched you can get 2 or 3 chains on one cassette in some cases.

Mind you it doesn't always work, but I find nickel plated cassettes (XT, etc) can give a decent service life if you get the chain checked.

Have your LBS check the chain for wear and stretch often, this should be free. If they charge for this 15 second service tell them to get bent.

......................................................................................................
On to the SS deal:
Use as big of a cog in the back as you can, more teeth = less overall wear and less chance of slip.

SRAM deraileurs have a strong cage spring, if you really want to go that FS route.

Run a 2:1 ratio, like a 34x17 or so, and make SURE the chain line is straight. If you don't your talking thrown chain during a sprint or climb. Cassette cogs are ramped to SHIFT, and they WILL at the worst moment if there is any angle from chainring to cog.

I have a lumpy healed collar bone and a permanently f**ked up shoulder to remind me of this fact.

Do you have a front chain guide? This combined with a strong deraileur and good chain line would make a SS FS work the most reliably, and that's what I'd think you'd shoot for in a 24 hr event.

Good luck, and test that thing on the trail WAY before race day !

 

[bomberz1qr20]

More on SS drivetrains, some good stuff:

http://www.surlybikes.com/spew/number3.htm

 

[BikeGeek]

Originally posted by bomberz1qr20

On to the SS deal:
Use as big of a cog in the back as you can, more teeth = less overall wear and less chance of slip.

<snip>

Run a 2:1 ratio, like a 34x17 or so, and make SURE the chain line is straight. If you don't your talking thrown chain during a sprint or climb. Cassette cogs are ramped to SHIFT, and they WILL at the worst moment if there is any angle from chainring to cog.

<snip>

I've heard that the Paul Melvin tensioner wraps the chain on a couple more teeth than a derailleur or Singulator can, helping to keep it from slipping. I haven't tried it, it's just what I've heard.

2:1 isn't required, but most SS purists will accept nothing else. Go with a ratio that fits the course you're racing: lots of climbing? maybe 2:1 is too stiff... lots of flats or downhill? kick up the ratio a bit to keep more speed. Your best bet if you're using a converted cassette hub with spacers is to pick up some shimano bmx cogs in different sizes. They're cheap, they fit a cassette hub, and they aren't ramped for shifting. Plus, with a couple different sizes in your toolbox, you can adjust the ratio as needed during the race. If you don't mind spending some dough, the King cogs are very nice, and, again, they fit a standard cassette hub.

 

[psycle-on]

Originally posted by swiss_less
Putting the old chain back on will fix the problem, guaranteed. Whenever you replace the chain or rear cog, you need to replace it's mate (replace chain, replace cog; replace cog, replace chain). These two pieces wear together, so if you just replace one, the two pieces will not line up perfectly which will give you nasty noises, and in some cases, skipping and chain dropping.

Thanks for all the advice guys! Actually putting the old chain back on DID work - problem solved! We appreciate it!

 

[SwisSlesS]

Originally posted by psycle-on
Thanks for all the advice guys! Actually putting the old chain back on DID work - problem solved! We appreciate it!

Ha! I knew it!

 

[wooglin]

I'm a little confused here. You're using an old ramped cog with its old chain? I think that the combination of flex around the BB/lower linkage and chain tension variation from the sus is going to be enough to throw the chain despite the derailleur/tensioner, probably at the most inopportune moment. I second the idea that you should put some hard miles on that set up before relying on it at 2am with little sleep. I'd be a lot more confident in a new chain and a new (bmx) cog. Maybe a new ring, too. You can always use them on the other ss when that drive train wears out.