I borrowed this from the SIC website, here is a direct link
You'll need to do a bit of visualization for this
explanation...so put away the Playstation 2 for a sec and
Think of your truck in its stock configuration....as the
wheels rotate, the axle wants to rotate the OPPOSITE
direction, right? And this
characteristic is what actual MOVES your vehicle...more
As the wheels rotate, the axle rotates the opposite way,
inducing motive force into the vehicle....now, this IS a
gross oversimplification, but it is a fact,
nevertheless....what is MORE important is that all the
OTHER drivetrain geometries...piniuon angle, anti-squat,
instant center....all VERY important geometries..are based
on this physical arrangement.
Think about braking, for a second.....in the stock
configuration,, when you hit the brakes, what happens?
Correct...the car has a tendency to dip, the rear has a
tendency to rise....but the rear is trying to rise "over" the
front leaf spring mount, right? And the basic lever
arrangement that is formed by the stock position of the
axle and the leaf spring tries to lift the truck OVER the
front leaf spring mount as the car brakes...follow?
This characteristic has the benefit of creating a fulcrum,
over which the truck is trying to "rise", and which induces
downforce during braking.
Lets talk about what happens during acceleration, for a
moment....when you acclerate, the axle/leaf spring
arangement has a tendency to want to "lift" the truck...and
this is because the axle is inducing force down the
centerline of the leaf spring, which forms a "lifting
arm"....basically, motive force is transferred down the leaf
spring to the approximate center of the vehicle, and this
lifts the truck...which in turn transfers weight back over
the axle, increasing tractive force at the tires....
Finally....since the point at which the axle rotates, up and
down, is centered around the front leaf spring
mount...pinion angle stays within limits.
Noe then......what about that reverse 4 link?
All bad, all the time. First off, when you arrange the links
to the REAR of the truck...the axle will swing on those
links, and EVERY time the axle goes up and down, those
links pull the axle towards the REAR of the truck....
Next...what about pinion angle? Well, reverse 4 links
NEVER solve for pinion angle, because they ALWAYS
make the pinion angle climb WAY positive, because the
upper links are ALWAYS shorter than the lower ones...
What about imparting motive force? Well, again...because
the links are behind the axle, when the axle rotates, the
links tend to pull the rear of the vehicle down....and this is
Finally, what about braking? This is where it gets
REALLY scary.....on a reverse 4 link, when you hit the
brakes....the links, which are oriented towards the REAR
of the truck, want to rotate UP and OVER the axle.....or,
more significantly, the axle wants to rotate DOWN and
BEHIND the rear of the truck....DEFINITELY an unsafe
So, why are revers 4 links "popular"? Well, fortunately,
they are becoming MUCH less popular, but the answer to
the question is...because they require NO knowledge of
vehicle dynamics, and they eliminate that pesky
requirement to actually ENGINEER a solution to that gas
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