The Fixed Innovations Axle Explained
This page explains the "theory" behind the Fixed Innovations axle. After
reading it you will understand better how the axle increases the number of
single-speed gears that will work on your vertical dropout frame.
(To order a Fixed Innovations axle,
With a single speed, and particularly with a fixed gear, the chain has to
be tight. That's because you don't have a derailleur to take up slack in
the chain. Slack makes the chain slap around if you're lucky; if you're
unlucky it can allow the chain to come off and lock the wheel causing
Now we come to dropouts. Vertical dropouts have become very popular
in recent years for some good reasons: they tolerate lower-strength
(a.k.a. "trick" or "lightweight") quick releases, and they hold the
axle firm against the huge forces generated by super-low mountain
bike gears. And they make changing wheels easier.
Unfortunately, they also prevent you from adjusting the distance
between your axle and your bottom bracket. That is, they make it
impossible to adjust your effective chainstay length and so to take up
any slack in the chain -- once you've removed your derailleur.
Whether a bike has vertical or horizontal dropouts, the slot for
the axle will be 10mm wide. This is because rear axles have
traditionally been 10mm in diameter. But in recent years many hubs
have been built around cartridge bearings, the most popular of which
is the 6001 which has an internal diameter of 12mm. So many cartridge
bearing hubs have axles that are 12mm in diameter along most of their
length but narrowed to 10mm at the ends in order to fit the dropouts.
The Fixed Innovations axle is just like "traditional" axles for
6001-cartridge-based hubs but for one change. As illustrated in the
pictures below, the 10mm end sections
are located touching one edge of the 12mm main axle body instead of
in the middle.
This means that as you rotate the axle within the dropout -- as you
can do when the quick release is open -- the 10mm section stays in
place but the rest of the axle -- and the hub and cogs -- move
relative to the bottom bracket. The difference between the longest
and shortest effective chainstay lengths on any frame using this axle
Here are a couple of small screen shots from the Java version of FixMeUp!. The light
blue regions in the center show the gears that are available on a
frame with 16.5" chainstays and a standard axle (left) and with a
Fixed Innovations axle (right). Note that the difference between the
effective chainstay length at the two ends of the blue region is only
The region you get without the axle is only about 1/4 the size.
Check out one of the versions of FixMeUp!
to see how this works for your bike.