Monday, November 24, 2008

Make it yourself chain tensioner

Check this out. A Deore XT rear derailler with a derailler cable end (ferrule still intact) holding it in the appropriate position to act as a single speed cable tensioner. It was on a cross bike which may explain the extreme spring tension being used (since those bikes get a lot of bumping action at speed).

This would be a great way to cheapen up your old bike -> single speed conversion. I'm sure any derailler would work.


1) Find a derailler nobody wants (probably easy if said derailler is a 7 speed or 8 speed model)
2) Mount derailler to frame
3) Cut the last 4 inches off a derailler cable you were going to throw out anyway because it's roached
4) Pull the derailler to the right position (upper jockey wheel under your single sprocket) and have an indefatigable person or zip tie hold it there.
5) Install the cable with the ferrule in the derailler adjuster barrel (turned out half way) and the cut end under the clamp screw
6) Have the indefatigable person let go, or cut the cable tie
7) Turn the adjuster barrel in or out to get that jockey wheel lined up just right with the sprocket
8) Thread your chain and pull the ends together such that you get the desired tension (remember, you can always start loose and cut some off)
9) Remove the unnecessary links with a chain pin tool
10) Use a SRAM Power Link* to put the chain back together
11) Ride

*awesome piece of kit


Jon said...

I just use the derailleur travel limit screws to lock it into place. The cable is not really a necessity.

-d said...

Hmmmmm... why would you need a chainstay protector if you're running a singlespeed setup?

-p said...

Can you use the screw that's in the derailler? Is it long enough, or do you have to find a longer one?

With the tensioner on there, there's enough compliance in the system that you can get some slap, just like a geared bike set in one gear.

-d said...

Interesting... do products like the Surly Singleator have the chain slap problem? It doesn't look like it would. I guess that's a small price to pay for the do-it-yourself rig. The Singleator is approx. $40, while the do-it-yourself setup could potentially cost nothing - if you have an old derailleur and inner tube (for the chainstay).

Mark said...

I tried this once but never thought to try the cable. I just used a zip tie to hold in position.

You might get some slap if your chain is too long.

-d said...

For extra aesthetics (and peace of mind), you could also use a cable crimp to cap the cut end of the cable to prevent fray...also a free addition. Most bike shops will give you a few sans charge.

GhostRider said...

Most chain tensioners (Singleator, etc.) for singlespeeds will give you a little chainslap unless the chain is EXTREMELY tight. Better to have a slapguard on the chainstay just in case...only a few grams of weight.

Mike said...

If the set screws on your derailleur are not long enough and you must resort to using something to hold the derailleur in place, a piece of spoke also works well in the place of a cable. Insert the head (elbowed end) of the spoke into the adjustment barrel, tighten the fixing nut down on the spoke as if it were a derailleur cable, and cut off the excess.

-p said...

Mike - genius idea. Just make sure to cut that spoke with a Vice Grip or something that can handle stainless steel (which will ruin your wire snips).