Why Reverse 4 link SUCKS!!

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RewT
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Why Reverse 4 link SUCKS!!

Post by RewT » 16 Jan 2013, 15:27

I borrowed this from the SIC website, here is a direct link

http://www.streetissuecustoms.com/reverse4.html

You'll need to do a bit of visualization for this

explanation...so put away the Playstation 2 for a sec and

follow along... :)

Think of your truck in its stock configuration....as the

wheels rotate, the axle wants to rotate the OPPOSITE

direction, right? And this

for-every-action-there-is-an-opposite-and-equal-reaction

characteristic is what actual MOVES your vehicle...more

or less.

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

NOT optimum.

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

arrangement.

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

tank location.
Getting a good deal is no reason to accept sub-par work, since making it right costs more later.
RewT Customization & Fabrication. Get it done right the first time!

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