Conversion to a single speed
 

Hello I have an early 90's GT terra outpost. It is all original and sat in a garage for maybe 15 years. The shifters are shot because they are from the age of the dinosaurs and I would like to make this bike into a single speed. Currently, riding it is a horrible experience because the chain keeps jumping, probably from no tension on the rear derailleur. I want to convert this bike for under 100$ so basically the cheapest way possible. Any advice? My local bike shop says I need to order a new, different kind of wheel. Can I still use this rear derailleur or do I need a chain tensioner?
http://bikeforums.net/attachment.php...hmentid=430658

would help to know if rear dropouts are vertical or horizontal. makes a big difference. took a quick google and couldn't find anything. but if they are, it can be as simple as:

1) remove front DR and shifter/cables and all chainrings. get 6 single-speed chainring bolts. put your choice of chainrings back on.

2) remove rear DR and shifter and cables.

3) remove cassette or freewheel

4) buy single speed (cog or freewheel) that fits your rear hub design. get extra spacers if cassette.

5) buy 7-speed 3/32" chain. shorten to length using chaintool. use master link to reconnect or not. your choice. most 7 speed 3/32" chains don't really need master links, IME.

i may be missing something, but not much. good luck. :)

If it has horizontal dropouts (and it looks like it does, you can do Single Speed without a tensioner.

Page down a bit on this site for a picture of dropouts, but ignore the suggestions about going fixed gear unless you are really looking that way, then it requires more than a single speed would.

https://www.google.com/url?sa=i&rct=...22397985087401

You can possibly convert for the price of a new chain if you aren't picky about gear ratio. Put the chain around the middle cog in front, and over the rear sprocket that lines up best in back... ensuring the chain is the proper length and ride away. I would probably use a 5-8 speed chain (they are all the same width).

It lacks the "cool" factor, but it could work for you. :)

Vertical dropouts. Just letting you all know.

bummer about the dropouts. oh well.

the simpliest way i know of, as has been alluded to in a previous post, is to leave the rear derailleur on and just use the high gear limit screw on the derailleur, turned in enough so that the chain rides on the 2nd or 3rd smallest cog. if that can be done the rear shifter/cable and housing can be removed permanently. if the gear is too high, i'd look into using the middle chainring mounted on the outside of the drive side crank arm as the chainring of choice.

i have, in the past, run a late 80's Dura-ace rear derailleur using only four cogs by adjusting the limit screws accordingly. they can have a dramatic effect. an extra long limit screw can probably be found at your local hardware store and may help.

Keep your whole drivetrain; ditch the shifters, cables, and housing. But save one cable. And if the chain keeps wanting to skip off the front chainrings, save the FD in place, but not cabled (use the limit screws for adjustment) as a chain guide:

http://www.bikeforums.net/attachment...9&d=1351442012

You can adjust the limit screws as others said, above, but this setup will give you more range -- you can set it up in the range you want or need, and you still get 2-3 gear shifting range with just the barrel adjuster on the derailleur. I left all the chainrings on, too. It wasn't often, but sometimes it was nice to be able to get significantly lower gearing when needed. If you're new to single-speed, something like this is also nice as it will give you a chance to try out different ratios until you get to the one you like best. This bike eventually lost two of the three chainrings and it pretty much stayed in the same gear out back.

Here's another ghetto SS conversion:

http://www.bikeforums.net/attachment...0&d=1354813338

I've never done it but i have seen ghost rings used successfully. that's where you put a cog of a large enough size to spread the top and bottom runs of the chain apart and it rolls merrily along behind the chainstay providing tension to the chain'
I think a pliable ring would really work well for this. They make them for industrial applications.
Roll-Ring Chain Tensioner from Renold

If it's a cassette,you can use a kit like this. Used one of those on a project bike once and it worked well. If it's freewheel,you'll need to use a freewheel cog instead. You can also just keep your rear derailleur as a tensioner,it'll just stick out further.

Google "magic gear" and have fun with that maddening little project.

It does have a cassette that kit looks like something I need.

with a 3/32" half-link you are never too far away from the magic gear of your choice. but it can be surprising how long it takes to hand file two steel drop-outs with a big rat-tail file. :lol:

If your chain isn't totally stretched out you can shorten it, skip the RD and try it on different combos right now.

some of those kits come with 3 cogs to try. Most cogs are too skinny, though, get a thick one after you find your ratio. Thin ones chew up freehub bodies.

i run 1/8" chain even on 3/32 cog. Plenty of $10 options.

In addition to halflinks,
Eehouse has a handy magic gear calculator.
Rennen Decimal Chainrings can help take up slack, but kinda spensive and not recommended for heavy riders.

For $30-40 you could buy a new rear shifter and cable and fix it up right and have gears. I'd be surprised if you needed a new derailleur, but even if you did, they can be had for under 30.

+1....Interestingly, I've known quite a few cases of riders finding a "magic gear" combo on bikes with vertical dropouts that works great for them, including singlespeed mountain bike and cyclocross racing. FWIW. :)

If you get a nice singlespeed chainring, you don't even have to get the chain all that tight. This one never jumped on me, even though I was worried about it all the time. Probably coulda gone up 1T on the front.

https://farm8.staticflickr.com/7439/...32486c7d_b.jpg

I run about that much sag on some of my IGH bikes, and I never throw chains.

Absolutely. I had one a few years ago. I still have the 43t chainring that was necessary to make it work. If you can find the combo that allows a tight (but not too tight!) chain, and a reasonable gear inch, it can be great. It's just a bit limiting, and as I said, it can be maddening if you just can't make it work.

I heard that there is a way to use a chain tool to make a bicycle a single speed if your derailleur hanger breaks. Could I do this so that I can at least ride it without having the chain jumping and so that I can get it safely to the bike shop for an actual new singlespeed wheel/wheelset

find a cog that lines up well with a chainring and then shorten your chain as much as you can so as to fit as well as possible. having bypassed the rear derailleur altogether.

this is what I got setup for now. a real chain tensioner is foreseeable in the near future.
http://bikeforums.net/attachment.php...hmentid=432000http://bikeforums.net/attachment.php...hmentid=432001

I don't know if it would be a PITA at this point, but looping the chain over the roller would be better. :thumb:

it was right in the middle and small bumps kept making the chain fall off. I slipped on some ice today and lost the bottom nut pictured above, and that is a new nut that i replaced it with. also I added some innertube around the chainstay so that it doesnt slide around. I cannot get the chain to stay on the way it used to in the middle but instead its riding on the fatter edge of the chain tensioner roller. its way tighter and seems much better but im having trust issues. the only problem that i hope doesnt happen is that bolt just falling right off again.

...and here's the same bike after figuring out a magic gear combo, using a half link:

http://www.bikeforums.net/attachment...1&d=1355160068

New wheel :D

http://bikeforums.net/attachment.php...hmentid=432101http://bikeforums.net/attachment.php...hmentid=432102

I am really starting to like this build.

You don't need a new wheel. You need a cog and spacer kit and something to tension the chain (assuming you don't get lucky on the whole magic gear thing - I never have). It sounds like your existing RD is broken/seized and won't tension the chain now. If so, you may be better off getting a simple tensioner. This spacer, cog, and tensioner kit has all the basics for under $40 (and the DMR STS tensioner works very well).

If you can rig up something to tension the chain, then you only need the cog and spacers which will set you back about $15. Your existing RD may work if you can get hit it with some penetrating oil and get it moving properly. If you have any mechanical skill, a tensioner is not hard to fabricate (I've even seen an old jockey wheel bolted to a bent up kitchen spoon). All comes down to what kind of value you put on your time.