1. What does this kit do?
This kit controls both the power and return chains on a Big Dummy, preventing
them from flopping up and down and swaying into things. If you ride on bumpy
roads, or offroad, having the extra chain control is really nice.
2. I don't understand the choices. What do I need?
The reason for asking about what type of rear wheel gearing you have is
because 1. Deraileur and internally geared hubs have a very different return
chainpath, and 2. The idlers can be used for tensioning the chain on an
internally geared hub.
The internally geared hub version is simpler, with fewer parts, so it costs
less. The deraileur version has a different chainpath designed to make sure the return chain
is up and away from the ground and from your kickstand.
3. How does it install?
A CNC machined clamp attaches to the diagonal tube coming down from the seat.
It is machined specifically for this kit and fits the tube perfectly. The mount
has an 8mm threaded hole in it that takes the stainless idler bolt. The idler(s)
go on the bolt, and are free to move side to side to track your shifts.
On the internally geared rear hub version, you slide the mount up and down
the tube to set the chain tension.
At TerraCycle, we make all sorts of specialized drivetrain kits for unusual
bikes (and trikes, and quads, and all sorts of things). We are xtracycle aficionados
ourselves, and we and a good number of our xtracycling friends had chains that
bounced around too much sometimes. We take care of problems like that on
recumbents all the time, so we designed solutions for the Free Radical and the
If your chain is rubbing on your wheel or fender, or bouncing around onto
your kickstand or even the ground sometimes, these kits are for you. They turn
those long, out of control chains into nice, under control chains. Gain ground
clearance and peace of mind no matter what crazy place you find yourself.
The attackment clamp is CNC machined 6061 T6 Aluminum with stainless clamp bolts. The clamp
is machined specifically for this kit, so it fits the Big Dummy diagonal tube
The Internally Geared rear hub version of the kit is designed to let you set
the chain tension by sliding the idler mount up and down. It uses a combined
Over/Under idler, with a power side and a return side idler in one unit. The
power side chain is carried on a 7075 AL cog, and the return side is carried on
a tough urethane chainbed. The idler rides on an 8mm stainless bolt.
The rear deraileur drivetrain version has two idlers, one for the power side,
and one for the return side. The ride on a common shaft, and rotate in opposite
directions. The power side idler carries the chain on a 7075 AL cog, and the
return side idler carries the chain on a urethane chainbed. The 8mm stainless
bolt that carries the idler is longer than the other kit and includes a
stainless steel chainkeeper to make sure the chains stay on the idlers where
they're supposed to.
The idlers are very low maintenance. The bearings are top quality ABEC 7
rated. The idler materials are abrasion , knock, and bang resistant and are
designed to take a lot of abuse.
Installation consists of installing the idler mount and adjusting the idler
position. If you have an internally geared rear hub, you can use the idlers to
set the chain tension. On the deraileur version. you can move the idler mount up
and down to get the chain clearance you want for your kickstand.
The idler mount attaches with two M5 bolts. Use a 4mm allen wrench to take
the clamp apart, then reassemble it on the frame. Tighten the bolts loosely, so
the mount stays in place but you can move it by hand if you want to.
Put the power side chains the cog, and put the return (lower) chain on the
grey urethane bed. On the internally geared idler, the power side chain goes
under, and the return side chain goes over. On the deraileur version, both the
power and return chains go on top of their idlers.
Adjust the mount up and down to get the desired chain tension/chain path, and
tighten the clamp bolts the rest of the way. You're done!
This kit is specifically designed for the Big Dummy cargo bikes. The mount is
machined for a 1-1/8 inch round tube. If you have something other than a Big
Dummy, and would like any of the parts of this kit in a different configuration,
let us know.