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Is a chain tensioner really necessary?

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Is a chain tensioner really necessary?

Old 07-20-17, 04:57 PM
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Oldbeaters
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Is a chain tensioner really necessary?

Hello all
I'm finishing up a single speed conversion on a bike I'm putting a motor on, and as I'm extemley cheap I haven't actually bought any parts for this bike, I'm running out of solutions to making my own parts. The last step is putting on the chain, but after doing some research I've found out that I need a chain tensioner. Now I refuse to spend even $5 on a chain tensioner purely out of principle, and I have made one, but it dosent fit around the cog because of where the bolt sits. ANYWAYS, after three or four prototypes I came to the stunning conclusion that if I just took out the extra links on my chain I could make it tight enough where I don't even need the tensioner. Is there some weird reason why you shouldn't take links out? Because if not then idk why anyone would buy a tensioner in the first place. I just don't want to do more damage then good and end up with a broken chain. Any answers would help thanks
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Old 07-20-17, 05:02 PM
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If your frame has horizontal dropouts, you can slide the rear wheel all the way forward to get the chain around the sprocket, then slide it back in the dropout to set your chain tension just right. If your frame has vertical dropouts, though, you can't move the wheel forward or back in the slot. That's where a chain tensioner comes in handy.
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Old 07-20-17, 05:03 PM
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Here again, the devil is in the details. If you have horizontal dropouts, you don't need a tensioner because you can slide the wheel back to get minimal chain slack (not tension). With vertical dropouts, that option is gone, so unless the length works out close serendipitously, you'll need to improvise something.
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Old 07-20-17, 05:06 PM
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If you have some type of horizontal or track dropouts on the bike, there is no reason for a chain tensioner. Just cut the chain to length, then pull the chain tight by moving the wheel.

Half links are available for some chains to make it easier to use short dropouts, or to give you a bit more adjustment.

If you have vertical dropouts, then it is much more difficult to ensure perfect chain tension.

Also keep in mind that as chains wear, they will stretch slightly. So, if your tension is perfect now, put 5000 miles on the chain, and the tension will be off.
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Old 07-20-17, 05:10 PM
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Being 1 link too loose is enough for low tension to be a problem.

Bicycles that are designed for single speed usually either have horizontal dropouts or track ends, allowing the wheel to be positioned so that the chain is sufficiently tight, without using a tensioner. This is why vintage road bikes are popular for 1x conversions; they just about always have horizontal rear dropouts.

If you don't have horizontal dropouts, then you either need a tensioner, or some other mechanism like an eccentric hub. Or, if you're really desperate, there are some kludgy solutions like fudging with the sizes of your cog and chainring to adjust chain tension.

This page is a good reference.
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Old 07-20-17, 05:22 PM
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I just made a chain tensioner out of an old derailer, for a planned project to put an IGH on a bike with vertical dropouts.
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Old 07-20-17, 06:22 PM
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Yup looks like I have vertical dropouts. I also made my tensioner from an old rear derailleur, so now I just gotta figure out a way to attach it without the bolt getting in the way. Thanks to all for help though.
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Old 07-21-17, 01:12 AM
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You need Some Form of chain tension adjustment
either horizontal dropouts -you dont have them
a dedicated chain tensioner -you dont want to spend money
a rear derailer used as a tensioner -go for it!

going the route of 'the chain is just the right length if I take out these links' doesn't work long term. Because chains wear down and get longer (pivots get looser) over time and then it's no longer the right length anymore.

so between constantly buying new chains, $$$ in the long run
or spending on a chain tensioner $ or modified derailer now
a tensioner/derailer is cheaper
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Old 07-22-17, 12:34 AM
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Put the chain on. Ride the bike.
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Old 07-22-17, 08:43 AM
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Originally Posted by Oldbeaters View Post
Yup looks like I have vertical dropouts. I also made my tensioner from an old rear derailleur, so now I just gotta figure out a way to attach it without the bolt getting in the way. Thanks to all for help though.
I don't understand.
You're talking about an SS conversion. So I assume the bike had a derailer before.
And now you can't fit a derailer.
What's up?
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Old 07-22-17, 04:44 PM
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Originally Posted by dabac View Post
I don't understand.
You're talking about an SS conversion. So I assume the bike had a derailer before.
And now you can't fit a derailer.
What's up?
The bike I'm doing the conversion on did have a derailer, but the chain tensioner I made was from a different derailer from a different crappy pacific bike. Plus I'm not just using the derailer as the tensioner I took the mount off the old derailer and used it to MAKE a new tensioner. The only reason it dosent fit is cuz the bolt is too big and since it sits in the old derailers spot, it hits the cog.
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