This is a set of notes I made on images I gathered from around the internet, mostly on mountain bike forums, about making a DIY chain tensioner for a single speed bike. One day I’ll make my own.

This first chain tensioner seems very simple. A piece of flat metal with a hole punched through at one end for a jockey wheel and a channel taken out of the other end to sit under the wheel tightening screw. The issue is that there is no spring in this method, so any tension put on the chain could stretch the chain, then the tensioner position would have to be reset manually otherwise the chain could fall off the jockey wheel.

This tensioner I feel is at the other extreme. It would require so much effort to make I might as well just buy a chain tensioner. It has a spring and I presume one of the pieces of metal attaches to the bottom hanger of the frame like a normal derailleur.

Adapted derailleurs

Usring an old rear derailleur seems like a great idea, as all the parts are available and they should fit onto the bike with few problems, especially if the derailleur is from the bike being converted. On both the examples below the rear derailleur has been tightened as far as it will go by snipping a small length of wire from the original gear lever and using it to lock the derailleur as far forward as needed. The first example only uses one of the jockey wheels, while the second uses both. Using both jockey wheels creates more chain wrap around the main cog, which reduces the chance of it slipping under a lot of torque. The only problem I can see with this method is that rear derailleurs can be quite heavy. I wonder whether certain bits can be removed?

This frankenstein is pretty interesting. It’s made out of a spring loaded brake arm from a mountain bike, with a jockey wheel screwed onto the end. I reckon this would be a really good option IF you already had the parts, otherwise gathering them all together would be a pain.

Frame attached chain tensioners.

These chain tensioners don’t attach to the rear mech hanger of the bike, instead they attach to the chain stay on the frame. Additionally, they tend to push the chain up rather than down, which increases the amount of chain wrap.

This one is made from a front derailleur with a jockey wheel screwed through the end. This one is easy to attach to the chain stay as front derailleurs often have adjustable p-clips to attach them to the seat tube on. Again there is no spring mechanism in this one so although it looks very simple, I would rather use something else.

This one is still a bit of a mystery to me. I think it’s a skateboard wheel, but it looks like the attachment is brazed onto the frame.

This one looks very easy to make, but I can imagine that it would increase the friction on the chain quite a lot as there isn’t a jockey wheel. I guess with this design one could easily be added however.

This one seems like a really great idea. All the parts should be sources and it has a pretty robust looking spring mechanism. Although this one is on a weird tandem setup, it could easily be attached upside down to a chain stay on a normal bike. It needs:

• 2 extension springs
• 1 p-clip
• 2 strips sheet metal
• 1 jockey wheel
• 3 bolts (1 to fit the jockey wheel, 2 arbitrary size)