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I'm upgrading an old bike with a five speed dérailleur system which I'm trying to convert to use a three speed gearhub from Shimano. I have assembled the wheel, I know how to set up the gearhub itself, but there's one question that bothers me: the chain.

Currently, the dérailleur pulls the chain and keeps it in tension. When I install the gearhub wheel, the dérailleur itself is ought to go away, but as I understand I need to keep the chain tight. Should I make it shorter or install another pulley? Is it possible to somehow reconfigure the dérailleur to pull the chain as a temporary solution until I do it properly?

The rear wheel as it is currently

  • Those are not technically horizontal dropouts, but they're near enough for this purpose. You should be able to slot an internally geared hub in there without a derailleur and it will just work. – Móż Sep 17 '15 at 1:15
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"Old" bikes – those from before the '80s or so – usually have horizontal dropouts that allow maybe 2 or 3 cm of fore and aft movement. That should give you enough room to tension the chain. I would think that a 5-speed bike would date from this era and be built with horizontal dropouts.

If that's the case then you can probably don't need a chain tensioner, just adjust the chain length so that it is long enough that you can get the wheel into the dropouts and short enough that you can get the tension right before you hit the back of the dropout.

Failing that, you could set up the existing dérailleur as a chain tensioner – either by leaving the shifter in place (and remembering to leave it alone) or by removing the shifter and cable and setting the limit screws to hold the dérailleur in place. You can also buy chain tensioners that are just "unshiftable" dérailleurs.

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  • I have added a picture so you can check the type of a dropout, I'm not sure this is a horizontal one (I don't have access to the bike at the moment, and this is the best picture I have currently, open it in a new window to see it full-size). – andrewsh Sep 16 '15 at 11:39
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I have a Shimano Nexus 7 internally geared hub. When replacing my chain, I have a chaintool to remove the pins to shorten chains, which usually start out the length intended for a dérailleur. When the chain starts to wear, I move the wheel back a bit in the horizontal dropouts.

See Sheldon Brown's entry for dropouts. I can't tell from your picture what kind of dropouts you have.

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Sounds like you know the chain will work with the sprocket on your hub. You will need to shorten the chain, if you use the same one.

It's usually better to get a new chain, and make the chain just long enough so that it has a cm or so play with the back wheel a little forward of the middle of the dropouts. As the chain wears (some say stretches) you will have to move the wheel back, until the chain needs replacing. It should last a long time.

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