For the most part, all G scale cars from the major manufacturers
come with truck mounted couplers.  Many modelers that have switched over
from HO gauge, would like to body mount their couplers.  USA trains has
molded a mounting pad on their new box cars to accommodate body mounting
of Kadee couplers, and I am sure Aristo will follow suit sometime in the
    The major consideration as to whether you should body mount or leave
your couplers as truck mounted, is in the geometry of the track in your
layout.  When you body mount couplers, you must have curves that are at
least 4 foot radius, and you must not have "S" curves.  These two
conditions will cause derailments, because body mounting is intolerent
of either condition.  I would recommend that you buy and read "Track
Planning for Realistic Operation " by John Armstrong to avoid the
pitfalls in track planning that contribute to these type of
derailments.  He gives an excellent commentary on "S" curves and how to
recognize and avoid them in your track plan.

    Here are the pros and cons of both coupler mounting systems:

    TRUCK MOUNTING:  Can be mounted on most cars without modifications
to the cars and couplers.  Car to car spacing tends to be much wider
than prototype spacing.  Handles 2 foot radius curves well,  and handles
"S" curves with little trouble.  Higher wheel drag due to truck cocking
on curves and through turnouts which can cause derailments.  More prone
to derail, especially on turnouts, and when backing  long trains into
sidings.  Higher coupler forces twist trucks and cause flanges to bear
on rails in curves causing derailments of long trains.  Couplers face
each other more directly, and will usually couple on 4 foot radius
curves.  Coupling on 2 foot radius curves is also possible.

    BODY MOUNTING:   Requires car body and truck modifications.  Car
spacing can be set to prototypical distances.  Requires larger radius
curves (4 foot or greater).  Cannot handle "S" curves.  Handles pushing
of long trains very well without derailments especially when doing
switching.  Lower drag on curves, allowing trucks to follow the track
which prevents derailments of long trains.  Will not couple on 4  foot
radius curves.

    If you choose to use Kadee couplers, you should also use their
coupler height gauge.  The device comes from Kadee in two versions:
#829 for #1 scale, and #880 for G scale.  This device makes it very easy
to determine if you have mounted the coupler at the proper height, and
it checks the operation of the coupler.  It also has a track and
wheelset gauge cast into the base.  A jig is attached to the bottom
which can be used to properly center and set the height of an uncoupling