It will work until you exert any braking to the drivetrain via the crankset. At that point, the forces on the tensioner will increase significantly and cause it to bend upwards (or be ripped off). If you were to build something to accomplish the task it would need a very strong (and probably triangulated) attachment to the chainstay.
Tensioners can work with freewheels, non-fixed planetary hub gears and cassettes because the resistance of the ratcheting mechanism and the tension in the drivetrain necessary to maintain chain tautness are the primary upward forces. These forces are much smaller that the forces exerted by leg braking.
Pure speculation: I'm wondering if the tensioner on the JT that initiated this discussion was intended to allow the use of a double chainring with a non-fixed SA hub. Positioning the tension arm idler at the center of the two chainrings would probably prevent the chain from unshipping.
Charlie Young
Honey Brook, PA
> It looks to me like the tensioner is not spring loaded. I.e. to adjust
> the
> tension, you would simply adjust and tighten the tensioner to take up the
> slack in the chain. Wouldn't a fixed tensioner work just fine with a
> fixed-gear setup?
>
> David Bean
> Arlington, MA