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I currently ride a single-speed converted bike (vertical drop-outs). I like the ride but feel that when I'm going for high speed on the road, I'm pedaling too much. Currently running a 18T cog on the rear and 42T on the crank, with a 2.333' ratio.

I'd like to increase the ratio and have a cassette on the rear hub, with a 16T cog. I'm wondering what's the best way of switching the chain to the 16T and keeping the chain tensioned.

Would it be as simple as removing one link from the chain or would the tension not be there?

As the 16T is one level down in the cassette from the 18T would the chain line be OK?

Thanks in advance for any advice.

EDIT: Here's a picture of the gearing setup to make it clearer:

gear setup

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How are you tensioning now? By cassette do you mean cog? –  Blam Jun 26 at 14:17
    
I bought the bike from a friend and it has the rear cassette still in place, with the chain on the 18T cog –  Chris Jun 26 at 14:20
    
Thanks Pete. I'm just on their website now. That's what I shall do! –  Chris Jun 26 at 15:23
    
I think I'm just going to run a tensioner or look into the eccentric hubs. Wish I knew about the tensioning stuff before I bought the bike but I got it for a good price. –  Chris Jun 26 at 15:27
    
I've emailed them so just waiting to hear back. Pete, do you know if I'll need to buy a lockring or will I have one on the bicycle I can use already? Going to purchase hub/spacer kit, 14T cog and tensioner. –  Chris Jun 26 at 19:25

5 Answers 5

If you poke around on the web enough, you'll find a "magical" gear ratio calculator somewhere. You input the length from BB to dropout and it spits out the front/back combos that will work w/o a tensioner.

Try this one.

http://eehouse.org/fixin/fixmeup.php

It would be much simpler to change the front chainring, if you can find a magical combo that matches what you want for a gear. There are also "half links" available that allow you to tweak the chain by less than a full 1 inch link pair.

FWIW, a single speed bike means your almost always in the "wrong" gear. Any change you make will only change when you're in the wrong gear, not the amount of time you spend in the wrong gear. If you're not happy being in the wrong gear, just buy a derailler and a shifter.

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I found a site a while ago called Velosolo, the guy who runs it seems to be quite knowledgeable about conversions, and he has a couple of kits on there - you might be able to get away with ripping your cassette off and replacing it with a cog and a bunch of spacers.

Because of the vertical dropouts you'd still need to tension the chain somehow (the obvious way being a tensioner).

That approach would certainly get you to a "fixed" state (an would allow you to change cog size on a whim), you might need to look a little more closely if you want to mix a hub in there instead, but it is definitely worth asking them the question - I've contacted this chap before and he's very helpful.

You might have to settle for less-than-perfect chain line, but at the end of the day the chain you're running right now is designed to traverse a cassette, so that's not going to be a showstopper. As regards chains, 1/8" is certainly the convention going back in time, but most fixed cogs & chainrings will also come in 3/32" variants, you should have no problems there.

If you do find something on the web, you'll first need to remove your existing cassette. To do this, you'll need an appropriate lockring nut and either a chain whip or a vice. Park Tools have a selection of nuts that fit just about everything that moves. If the cassette is either Shimano or Sram, you'll need one nut (FR-5, but double-check), if it is Campy you'll need a different one (FR-11, but double-check). In my experience, its a lot, lot easier to stick the cassette into a vice than to use a chain whip. As a tip, a Black and Decker workmate makes a great vice!

Your other alternative for removal is to take the wheel to your LBS and ask nicely. For someone with the right tools it really is just a 30-second job, you might find if you ask them nicely they'll loosen everything there and then, and not charge you... But if you did this, convention is just to buy something (anything) from them as a token of thanks.

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Velosolo stuff is good, bought a spacer set and tensioner from them this week. Arrived today and all set up in 30 mins max inc shortening chain, yet to test ride but all looks and feels good. If it's a disaster I'll let you know! –  Stamfordone Jun 28 at 22:24
    
@Stamfordone yes I also had a good experience of them –  PeteH Jun 30 at 22:27

Sounds like you have multi-speed cassette, no derailleur, and no chain tensioner. On the 18T you have good chain tension. Even in this set up as the chain stretches you will get slack on the 18T.

Moving to the 16T is not full chain link. A horizontal drop out is typically a little longer then one chain link. If you get all the way back and have slack then you take out link and you will be up in the horizontal drop out.

I assume chain line would be OK moving one gear as you probably still have a multi-speed chain on it. But you are going to have slack.

If you want to ride single-speed then I think you need to go to true single-speed set up with a tensioner. Another option is to put a derailleur on that bike.

Single-speed conversion is not that difficult. Nashbar has a single-speed conversion kit with spacers, three cogs, and tensioner with shipping is like $30. I have seen the cogs in sizes 14T, 15T, and 17T and sizes 16T, 18T, and 20T. Yes you can pay more for higher quality but I have one and it works. Most single speed cogs are 3/32 and I have seen 1/8 (White). Your front chainring looks OK so I would not replace it. When you do replace the front chainring then go single-speed. At then you could go 3/32 or 1/8. If 1/8 then need to go 1/8 chain. 1/8 is more metal and longer life. 3/32 or 1/8 there are single speed specific chains - they are cheap just get one when you order you kit. I run 3/32 cogs with 1/8 chain and chainring - I don't think they have to match. You should replace your chain when you replace the chainring. Not a given your bike would even take an eccentric hub and they are more expensive.

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So as its a vertical dropout I have no choice but to run a tensioner. I'm just trying to keep it minimal and very low cost. I'll buy a single speed hub kit and a tensioner - will I need a new single speed 1/8" chain? And can I keep the crank or will I need a different one? Thanks for your help –  Chris Jun 26 at 15:03
    
Same crank. When you replace the front chainring get a single speed but would wear out what you have. I still would not give up on finding a used derailleur and shifter unless you want single-speed. An eccentric hub is a type of chain tensioner but a simple spring type will be cheaper. –  Blam Jun 26 at 15:08
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@Chris 1/8" chains are stronger but you can just as easily stay with 3/32". The key is just to make sure that the chainring and the cog are consistent with each other. –  PeteH Jun 26 at 15:20
    
@Chris I would assume to put a derailleur but with no cable, and adjust it to proper cog. Later you can readjust it to other cog and ratio. And your chain will always be tensioned. As you don't mean to really use gears, you can get a cheap derailleur. –  Alexander Jun 26 at 20:08
    
@Alexander A derailleur without cable the spring push it out. If you are going to mount derailleur then might as well add shifter. –  Blam Jun 26 at 20:48

You can simply add a cheap chain tensioner and be done with it. The chain line will most likely not be ideal anyway if you left the entire cassette on there, so that shouldn't be a concern.

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I'd prefer not to use a chain tensioner. Guess I have to try adjusting the links. Long-term, to remove the cassette - would I just need a new hub and spacers? –  Chris Jun 26 at 13:59
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Better get a dedicated singlespeed/fixed gear hub with 1/8" drivetrain. They last much longer in my experience. You can also get eccentric hubs to allow for chain tensioning. If you don't want a chain tensioner, you won't get good chain tension for all sprockets. One link less will probably be too much to go from 18 to 16. Also, your chain tension will reduce with chain wear. This could lead to unnecessary chain drops if you go through potholes or over curbs. –  arne Jun 26 at 14:14

So this bike at one time had a derailleur, right? But you only want to ride with one of two rear cogs now? And whichever you choose, you'd stick with that one for the whole ride? If so, I'd be inclined to pop an inexpensive derailleur on there to provide the correct chain tension in either cog. Then I'd just use the derailleur limit adjustment screws to shift from one cog to the other as need be.

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