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Old 10-16-07, 09:46 AM   #1
flats
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double chain ring to single conversion

I realize this may the question of a noob, but I am just curious if anything special needs to be done to convert a standard double chain ring to a single chain ring (effectively cutting the bike from a 20speed to a 10speed)? Do you need to buy a whole new crankset? Or can you just take the derailleur and one of the rings off? Thanks in advance
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Old 10-16-07, 10:00 AM   #2
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It generally depends on your cranks, but I'd say you could probably do it.. I wonder if you'll be able to access all of the 10 gears on the rear though as the chainline will be pretty off on the gear furthest from your chainring..

Jer
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Old 10-16-07, 10:06 AM   #3
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without a derailleur, you may have a heck of a time keeping the chain on. It will tend to derail especially if you are in any gear other than whatever one has a near-straight chain line. Bumps will greatly exacerbate this problem.

If you use something like a Jump Stop and a outside chain guard of some kind it probably can work. The best thing is to use double chain guards on both sides of the chain ring like on this bike:
http://www.performancebike.com/shop/...tegory_ID=3040
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Old 10-16-07, 10:53 AM   #4
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.. I wonder if you'll be able to access all of the 10 gears on the rear though as the chainline will be pretty off on the gear furthest from your chainring..

Jer
What about going from a triple to a single? I took off my FD and am using only the middle chain ring. How can I tell if the chainline is right? Sp far I have had no problems, so I am thinking about waiting until after the winter to get a single set up for the front.
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Old 10-16-07, 11:22 AM   #5
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if it is a straight shot from the middle ring to about the middle of the cassette, then your chainline is about where it needs to be.
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Old 10-16-07, 06:27 PM   #6
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bump
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Old 10-16-07, 10:13 PM   #7
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I have a bike in a similar situation ... but I got there to opposite way. I built up a Surly Cross Check as a single speed (using wheelset with 9 speed compatable freehub ... used spacers). I found that I needed a little gearing. I ride this bike in mostly flat'ish areas (converted "rails-to-trails"... but throw in some incline and a little wind and a few speeds can be darned handy.

I pulled off the spacers, slapped on a 9 speed cassette, added a downtube friction shifter and a cheap deore rear derailer now I have 9 speeds in the rear and a single speed sugino track crankset up front. The chainline runs dead on the middle cog and I can shift into the top or bottom gear with no problem at all. Works very well for my purpose.
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Old 10-16-07, 11:02 PM   #8
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Originally Posted by krash View Post
without a derailleur, you may have a heck of a time keeping the chain on. It will tend to derail especially if you are in any gear other than whatever one has a near-straight chain line. Bumps will greatly exacerbate this problem.
Have you actually experienced this?
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Old 10-17-07, 12:04 AM   #9
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Have you actually experienced this?
i have but not since i've used a third eye and chainring guard.




ed rader
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Old 10-17-07, 07:20 AM   #10
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Have you actually experienced this?
Refering to the chain falling off the chainring when shifting. This drove me crazy and it got to the point where it was happening on virtually every commute. The culprit turned out to be the ramped chainring from the original crankset. Rocket Ring makes a bmx chainring w/110mm and 130mm bolt pattern. This is about the cheapest option...I've got 2 bikes set up w/them for commuting. 48t to 38t are the size ranges. Available @ bikepartsusa.com. harriscyclery.com Vuelta makes TT chainrings up to 60t unramped, but they're expensive...80-90.00 per. The RR are 15-20.00. FSA has a series of 'messenger' chainrings, but they're expensive, also.

Get some bmx chainring bolts or go to a hardware store for 3/8" star washers to take up the slack of the missing chainring. Single cr bolts are a much better option, though.

Make sure to size the chain properly, also. sheldonbrown.com has instructions on how to do this.

Just recently I purchased the Sugino 103mm bb and the matching 48t single crankset from universalcycles.com and have to say I'm very pleased w/t setup. The bb is very smooth. I use the setup w/an 8sp cassette and old Shimano bar-end shifter. The next most narrow that I know of other than the Phil Wood 103mm bb are a Shimano 107mm or Stronglight 107mm. Both are available at bikepartsusa.

BTW, since going to the unramped single chainrings I've never had a chain fall off when shifting on either of my commuters or my roadie.
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Old 10-17-07, 08:54 AM   #11
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yes I have experienced the chain derailing constantly with a single up front and 9sp cassette in the rear, even when only running in the middle cog with a very straight chain line. Of course this was riding offroad. I imagine it may stay on most of the time without all of the bumps.

An unramped chainring with full height teeth (SS ring) will probably improve things, but for me even just the deflection from turning the cranks and torquing the BB is too much risk. If it has any odds of falling off, I won't ride it.
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