I get a lot of emails about cyclocross (I love it dont get me wrong) but I thought, Id pose this reader question to the World Wide Web of Plus One Lap readers. As well as posting my response.
"I've recently re-set up my c-cross bike, and i have a single chain ring up front, but when i ride it hard, over logs or curbs
(as it is used for commuting too), my chain pops off. a friend of mine recommended
just putting on a front dérailleur to keep the chain on, but i am having a hard time 'adjusting' the dérailleur to deal with the nine speeds in the back. is there anything i am able to put on in place of a dérailleur to keep the chain on that is not some freaking down hill thing?
thanks for your help
Paul"
This is very common. There are several options to hold the chain on in the front (Chain ring guard with a Deda Dog Fang or NGear Jumpstop; an old Front Derailleur or 2 chainguards that go on each side of the chainring, and maybe others?)
I have used, the Dog Fang, NGear, and a Rohloff Chainguide that looks basically like an old front derailleur but it costs like $50. I have never used double chainguards. What I have used didnt work. Not well enough at least.
With the fake front derailleur option, the chain will rub on the derailleur no matter what on one of the extremes, and if you space out the derailleur by bending it, there will be enough space for the chain to slip past it. With the Dog Fang or Jumpstop I still had a problem with the chain bouncing off, even after I shortened my chain to the right length.
Maybe the dual chainguard is the solution that works? The funny thing is, the single chainring has a myth that its the chaindrop solution, but I've known more people to drop chain with a single ring than with a double.
You could always, rig up the front derailleur and have a shifter going to it, but only having one chainring. That way, you could adjust the rub, but still have just the one ring. But if you're going to do that, why not toss on another chainring and double the amount of gears you have?
So my answer? Try double chainring guards, shorten the chain, perhaps running a chain tensioner in addition to the derailleur might help (like the Kore tensioner or the Dimension tensioner posted above) or do like I did and go either double ring or Singlespeed.
Does anyone have a better idea?
5 comments:
I personally run the full set of gears, (I use the NGear even with the front deraileur & 2 chainrings...so I gues I am just paranoid) however I know lots of guys that run the single chainring up front setup.
The most successful thing I have seen is a combo of what you suggest: An outer chainguard and then the NGear on the inside.
The two guard option works great if you are ready for some headaches along the way. Your woes will vary with what type of crank bb interface you have. Basically you are always playing with chainline and spacing to make things work. The usual way to do things is to run a gaurd in the outer position, the chainring in the inner posistion, another gaurd inside that spaced the thickness of your spider tabs, and all held together by longer chainring bolts. Some times you have to lengthen your spindle to make the inner guard work. Use the thinnest guards you can find. FSA makes the skinniest, but they are expensive and fragile. But remember you aren't supposed to be using them as DH rings, just to keep your chain from jumping off. Be prepared to spend time with micrometers and the obscure section of the parts bins looking for just the right spacer thickness and spindle length. If you run octalink, the common solution is to switch from a double 109.5mm to a triple 118mm. It can mess up your chainline to go that wide. XTR uses the same spline and is available in 112mm and 116mm lengths. The new external BB stuff doesn't have any room for shifting chainline. You will most likely, depending on your chainstays, need to run the chainring inthe outer position and space the outer guard outside of it. Square taper is the easiest because the come in all sorts of length spindles, unless you have a Campy crank. Their taper is different than JIS. Don't be tempted to put a Campy crank on a JIS BB. You will wind up cracking the arms. ISIS is actually fairly easy as there are a few different spindle lengths and many of the BB's don't have a shoulder on the drive side cups, which allows you to shift the BB from side to side a little. Whatever method you choose, shorten your chain as much as possible and learn to set your bike down smoothly. Iran a double guard with zero chain drops and no rubbing all last year, but it took some experimenting. Email me if you have any questions. thomkneeland@yahoo.com
This sounds like a chain length issue to me....the chain should be as short as possible when in the largest cog on the cassette. This should allow the derailleur to keep enough tension on the chain to stop it getting dropped. Chainline, like the previous poster mentioned, also comes into it. tristan at wheelworks dot co dot nz
I am running a outer chain guard (salsa)and an Ngear Jumpstop($14 cheap). The chain is as short as I can get with a 12-27 on the back. I adjust the Ngear as per its instructions - close to the chain when in the 27. With this setup I seldom to never have chain drop problems even when doing single track with my mountain bike buddies, I beat up lots of wheels and get in lots of running in this exercise but do not drop chains.
help from denver colorado
I've got double guards 1x9 on my race bike. It's a little heavier than 1 guard and a jump stop, but no dropped chains in 4 seasons of CX. Don't forget to shorten the chain when you go single.
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