Picture of DIY Bicycle Chain Tensioner
Chain tensioners and guides are often used in "extreme" mountain biking such as downhill, freeride, and fourcross. They are used to stop the chain from bouncing around and falling off. However, they are very expensive for a simple item, generally ranging from 30 to over 100 euros. This is a simple way to make one that costs almost nothing  and you probably already have the materials! Also, chain tensioners can usually only be used with one or sometimes two front chain rings. This one works with three!
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Step 1: Materials

Picture of Materials
1) Rear Bike reflector

2) Small piece of garden hose

3) Ziptie(s)

4) Scissors or something else to cut with

5) Phillips Head Screwdriver

Step 2: Take Apart the Reflector

Picture of Take Apart the Reflector
Take out all of the nuts and bolts from the reflector. You can discard the reflecting piece but keep the rest as you will need to put some of it back together.

Step 3: Add the hose

Picture of Add the hose
Take the piece of hose and put it on to the round part of the reflector. It will not fit on easily so I recommend either putting it in boiling water or holding it under a small flame (quickly - don't burn it!) to make the process easier. It only needs to cover the plastic circle so trim the hose if it is too big.. I had already made my tensioner so I didn't put the hose on the whole way because I still needed that reflector.
FileBravo9 months ago
Great! I like to see the face of the mechanic when he finds pieces of diy on my bike:-)
I can grant that this solution is really robust. I made it on my trek. Pictures with my phone are quite dark...
Iw-Munt2 years ago
Love it! Hope it will be OK with my SS project, if not I'm gonna stick it on my xc bike. Thank you
Zsombee2 years ago
instead of garden hose, i'd like to use inner tube - is it a good idea?
GuitarGuyJames (author)  Zsombee2 years ago
Eh, I would recommend the garden hose for two reasons:
1) More durable, and
2) More slick.
The innertube would probably work, but there would be more friction and it could wear down. So... if you have garden hose, use that. If not, use the innertube.
tutdude982 years ago
How do you make chainstay protector?? is that old innertube
GuitarGuyJames (author)  tutdude982 years ago
Yeah, I just cut open an innertube, wrapped it tightly around the chainstay, then ziptied it on.
when i broke my rear derailleur it was scratched down the protective film :P so i need to make something like this
GuitarGuyJames (author)  tutdude982 years ago

Use this website but you don't need to take the wheel off.