Chain tensioner.

[fredintoon]

Extended frame hardtail builds often use a spring loaded chain tensioner which needs some kinda frame attachment.
The maintenance free self adjusting roller chain tensioner from Mcmaster-Carr
http://www.mcmaster.com/#chain-tensioners/=t5djya
Just sits there, eh?

 

[lowerc]

Yes it just sits there but it's designed for low speed applications.
I just did some rough calcs and at 60mph the chain is moving around 1200 ft/min

Also, don't think it is designed for different primary and secondary sprockets.

I wouldn't trust it to stay in there at highway speeds.

 

[BriggsStratton]

I'm interested to read if anyone has used this on a bike. A few months ago I bought a parts bike from a guy that was using a regular old sprocket as a tensioner (just floating in the chain, like this) and he said his hadn't ever fallen out. Seems like it could be dangerous. Interesting looking though.