The who, what and
where of e-cycling’s
most popular
motor option
Mid-mounts, mid-drives, cen- ter drives—whatever you call them, judging by the number of
test bikes that have come our way over
the last year, putting the drive system in
the middle of the bike apparently makes
a great deal of sense.
What are the advantages of the
design over hub-drive systems? Most
important is the fact that the e-assist
gets to use the gears, so the power is
more effective over a wider range of
speeds. Second, the wheels are normal
bicycle parts that can be sourced from
many places and serviced at any bicycle dealer. Plus, many mid-drives use a
relatively small motor, so these drives
can be quite efficient and frugal when it
comes to using up battery power.
DRILLING DOWN
So now that the basic goodness of
mid-drives has been established, let’s
take a look at the mid-drives currently
found on the market. Some are neatly
packaged in a drive case that requires
a frame with a motor mount instead of
a bottom bracket. Others are designed
to fit a normal bottom bracket. These
packaged mid-drives use a motor that
uses internal gears to gear the engine
down to an rpm that is useful for bicycles.
Other mid-drives use an external
motor on a frame mount. Most of these
transfer power into the drivetrain using
an additional chain from the motor to
the cranks. This can be accomplished
with a crankarm with a chainring on
both sides, or with an added chainring
attached to the existing chainrings.
In some cases, the external motor
has internal planetary gears, and that
gets by with a single chain from the
motor. Others have no internal gear
reduction, so they need a double external reduction to get the motor rpm correct for good pedaling cadence.
Some of these drives are sold for
aftermarket use to modify an existing
bicycle, while others are only available
as part of a complete bike. Most are
legal for the U.S.; however, some are
far too powerful to even be considered
a bicycle. The one caveat that we insist
on passing on is that everyone needs to
be responsible if they choose to build
a high-powered model. If it needs to
be registered as a moped or even as a
motorcycle, do that and avoid causing
problems for yourself and others.
