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Old 07-23-08, 09:48 AM   #1
ShadowGray
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Final questions for single speed conversion

Okay so I have an old 90's steel mountain bike with vertical dropouts that I'm converting to single speed using a tensioner. I have my tools on the way and I'm getting the Performance tensioner kit and a single speed SRAM chain. But a few questions left:

1) For the cranks, can I just pop off the inner chainrings and leave the big one on? That should hold by itself, right? Or do I need a dedicated single speed crank?
2) For the chain, how long should it be? Just enough for the biggest possible combination (48-20)? I'll probably be running (48-16) most of the time, even 48-18 felt too lose when I tried it with gears. I assume the chain will come with more than enough length.
3) How stable is the tensioner from Performance? It doesn't look like it has a cage to hold the chain; is it possible that the chain will fall off?
4) Anything else I should know for this?
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Old 07-23-08, 10:55 AM   #2
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Wait, I thought you were making it a single speed. Figure out which combination you want before you shorten the chain. Once you have that set, put the chain on and size it appropriately. You will have a little leeway if you want to change gearing up or down a tooth.

Chainring-wise, if I were you, I'd use your middle ring. With your big ring, I think you'll have a tough time finding the appropriate gearing, especially if you're planning on using it as a mtb. You'll need to mess around with the SS spacers on the rear wheel to get the chainline right - it's important to get it as lined up as possible.

No ideas about the performance tensioner. As the chain is not moving anywhere side-to-side, there's really no need for a cage. Just needs to be enough spring to keep your from derailling.
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Old 07-23-08, 11:04 AM   #3
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Originally Posted by tellyho View Post
Wait, I thought you were making it a single speed. Figure out which combination you want before you shorten the chain. Once you have that set, put the chain on and size it appropriately. You will have a little leeway if you want to change gearing up or down a tooth.

Chainring-wise, if I were you, I'd use your middle ring. With your big ring, I think you'll have a tough time finding the appropriate gearing, especially if you're planning on using it as a mtb. You'll need to mess around with the SS spacers on the rear wheel to get the chainline right - it's important to get it as lined up as possible.

No ideas about the performance tensioner. As the chain is not moving anywhere side-to-side, there's really no need for a cage. Just needs to be enough spring to keep your from derailling.
I am, but it comes with 3 cogs - 16T,18T, and 20T. Normally I'd be using the 16 or maybe 18 for heavier loads, is that too much difference between cogs? I'm not quite sure what the middle ring is but it's generally too low for me; when I'm unloaded I ride with the biggest ring in front and smallest in back fine.

It's going to be a pure commuter/utility bike, so I don't need low gears, especially in this flat city.

And how do I determine the right chain length? Should it just be enough to go around the gear and cog + 1 link? Or just enough without any slack?
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Old 07-23-08, 11:14 AM   #4
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I'm pretty sure the kit comes with 3 cogs for you to choose from, but you'll only install one. I could be mistaken, though.

Whatever you like to cruise in on your current setup is probably a good ratio for the single speed. Check out Sheldon's Gear ratio calculator. Plug in your current favorite and see what will work with your big ring to duplicate that.

As far as chain length, I think you'd want to set it up so that the tensioner is midway through it's travel, especially if you're planning on swapping out cogs to fine tune and don't want to resize the chain.
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Old 07-23-08, 11:17 AM   #5
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Check out Park Tools' website to determine the correct chain length. I'd recommend doing what you said last. Make it just long enough to go around the gear and cog. 48/16 is a pretty steep gear. I have 42/16 on my fixie and it's just about right. I do have some minor hills around here though. If I were you, I'd make the chain long enough for the 20t cog and let the tensioner take care of the slack. Then I'd shorten the chain later if you find that you prefer the 16t or 18t cog.

What kind of crank do you have? If its the common kind with little bolts going through a spider to hold the chainrings on, you'll probably need single stack chainring bolts. Otherwise the bolts for the big chainring will be too long when you remove the middle chainring. The single stack bolts are only $5-10 at your LBS.
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Old 07-23-08, 12:21 PM   #6
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Yeah, I run 48/16 on my fixie and it's steep. Because I'm a cheap bas*ard, I just took my old stack bolts and ground off some of the female part. Works great.
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Old 07-23-08, 12:55 PM   #7
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I could easily grind them off here at work. Nothing like an opportunity to use the rotational grinder.

Is there a problem with leaving the bolts long anyway? Is it just an aesthetics thing?

I don't know if 48/16 would be so bad. I normally run 48/16 on my bike gears, maybe 48/14 if the road's good and I'm active.

But once I put in the single speed cog, should that generally be the one I stick with? The idea is that I might want to swap out cogs depending on riding conditions.
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Old 07-23-08, 01:06 PM   #8
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If you want to change gears, you want gears. You will not want to swap these cogs out, and you'll find that once you choose the right gearing, you won't even think about changing it. Generally, you want to choose a ratio that's a little lower than what you would cruise in on a flat, to give you climbing options. It's okay if you can't crank at 25 mph, but you want to be able to climb.

You need short stack bolts, otherwise your ring is flopping around.
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Old 07-23-08, 03:59 PM   #9
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I'm pretty sure the kit comes with 3 cogs for you to choose from, but you'll only install one. I could be mistaken, though.
As far as chain length, I think you'd want to set it up so that the tensioner is midway through it's travel, especially if you're planning on swapping out cogs to fine tune and don't want to resize the chain.
You can probably install 2 cogs and, if your chain is long enough, use your fingers to shift between them as desired. You should be able to do that with the use of a chain tensioner. Don't forget to stop and get off the bike to shift.
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Old 07-23-08, 04:11 PM   #10
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You may be able to do that, but you'll probably have to move the chain tensioner over too, or it'll shift the chain for you automatically back the cog it is positioned under.
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Old 07-23-08, 04:47 PM   #11
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You may be able to do that, but you'll probably have to move the chain tensioner over too, or it'll shift the chain for you automatically back the cog it is positioned under.
Right, but would only take a moment with a hex wrench with a Surly Singleator.
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