|   somwhat SS | dogmny
Feb 16, 2002 9:50 PM | | I just yanked the smaller gear and derailur off the front of my seven road bike and had a question for the other sick minded around here. The other day I was riding her and when shifting into the 11 tooth ring the chain poped off the front. The only two things I could think of to cure it is to 1. replace the front gear with an engagement ring (wich I have allready ordered and 2. make the rear casette smaller. the question I have is on the latter. can I gut the 8spd casette to a 6 or 5 speed?
dogmny |
| re: somwhat SS | Brian Robinson
Feb 17, 2002 1:38 AM | | Yeah you can use part of the cassette. In fact, my last "geared" mountain bike had a single ring up front and the 14-21t part of a Dura-Ace cassette. You'll have to use spacers to take up the rest of the space on the freehub body, and you'll have to use the smallest cog for the lockring. |
| re: somwhat SS | dogmny
Feb 17, 2002 7:03 AM | | what about ramping? I want to keep my hardest gear and the second to the easiest(we got hills)can I mix gears?
dogmny |
| re: somwhat SS | Brian Robinson
Feb 17, 2002 1:26 PM | | That makes it a bit more complicated. You run the risk of having odd sized jumps in the cogs, which it won't be ramped properly for. Also, the derailleur follows a predetermined path, so you will have to adjust the b tension screw to prevent rubbing while in the bigger cogs, particularly if you are spacing the biggest cog out from the freehub body. What will happen, is that as you adjust the derailler to not rub, the gap between the derailleur and smallest cogs will increase, added to the fact that if you skip cogs, the gap will not be consistent. As such, your shifting may not be all that great. It is entirely possible that it will work flawlessly, but chances are that it won't. Using a mountain derailler could improve your chances as they are designed to accept a wider spread of cogs.
Good luck |
| re: somwhat SS | lcunnion
Feb 17, 2002 8:39 AM | | For the sake of clarity:
chainrings - gears found on the crankset; shifted by the front derailleur.
cogs - gears foundo n the freehub; shifted by the rear derailleur.
So what I think you are saying is that you have removed the front derailleur as well as the smaller of the two chainrings (which I assume would be the 39T).
You are planning to replace the remaining chainring (the 53T) with a similar size ring distributed by QBP - the engagement ring. The reason for doing this, I assume is that an engagement ring is an unramped/unpinned chainring and you are hoping that it would be less inclined to throw the chain off the chainring.
Your problem is that, when shifting to the 11T cog, your chain likes to come off the chainring.
Did I get all that straight?
If I did, I _think_ the problem is that there is nothing to guide the chain up front. This would normally be the task of the front derailleur, but you have removed it. The front derailleur plays two important tasks: (1) it shifts the chain from one chainring to the other (or the third if you run a triple) and (2) it keeps the chain centered on the desired chainring.
Now, your thoughts are running along the lines of "if I don't need to shift chainrings, I don't need a front derailleur." you are correct.... but I think only halfway so. you still need something to keep the chain from wanting to pop off during extreme chainlines while under load.
I think your options for a 1x8 or 1x9 or 1x(anything except 1) drivetrain would be to either leave the front derailleur on to guide the chain (you can lose the shifter if you are trying to save weight). or get a bb-mount chain tensioner, the likes of which DHers use to keep their chain from tossing. The first option would be cheaper as well as lighter as well as quieter, but you might want to leave at least a downtube or bar-end shifter on the bike so as to be able to trim the derailleur (campy ERGO will also work, but STI is a pretty miserable choice for trimming the front derailleur. I say this despite my overall preference of shimano over campagnolo).
now the point where I'm not sure is that your chain seems to be launching on the 53x11 which is not an extreme chainline in the least. Perhaps the chain goes with a little deflection, but that cog position and that chainwheel position were made for each other. Perhaps it is because at this point the rear derailleur is at its (now) slackest position and I assume the drivetrain is at a large load (it is the your highest gear currently).
Hope this helps and morever, I hope you are able to solve your problem,
Linh "you can always turn it into a singlespeed" Cunnion |
| a few more words | lcunnion
Feb 17, 2002 8:50 AM | | it's not that i don't think a 1x(multispeed) system couldn't work without some sort of chain guide up front. i'm sure in a large number of instances, it wouldn't be so necessary (especially as your gear combo approaches a perfect chainline). but i think that a guide would help serve as a preventive measure for just those situations where the chain does want to go off the chainring. |
| Another option.... | Karkus
Feb 17, 2002 3:03 PM | | I tried something like you're trying to do about a year ago, but I ended up with 2 chainrings in the front and only one cog in the back. You can keep whatever chainrings you have and get one of those Shimano DX BMX cogs without the ramps (they come in 14,15,16,18, I think) and fill the rest of the cassette with spacers.
Check bontrager.com for his rant on building a single speed and the dual speed option, which even allows you to get rid of both shifters by using your hand to shift on the front. Keep the rear derailleur as a tensioner (put limit screws in to keep the chain on better) or get a SS tensioner.
I'm happy with this setup on one of my MTBs. It works for wannabe SS riders like me who live in mountainous areas. |
| Another option.... | dogmny
Feb 17, 2002 9:46 PM | | You all have been great help. just to clear things a little. My mountain bike is a SS and I cant convert this one cuz of the fragility of the rear hub(DT HUGI) so Im stuck running a multi geared cog on her. second she is a beautiful Seven that Ive been hoarding and use her to commute to work. and just to top it off I have 8 good hill climbs between here and work and not enough downhill angle to get moving without having the harder gears. So all said Ive got to get ingenious and make her work as an 8spd. Im gona try the engagement ring and see how it works 1st and I think(since you reminded me about chain length) Im gona check and see if there is any extra I should take out of the equation. once again thanks and Ill let you know somime this week.
dogmny |
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