Rear Suspension Type Ideas

[zerotofear]

Truck Arms.

[DynoDon]

Not a fan of Truck Arms. Tons of unsprung weight, in the way for exhaust, The arms themselves by nature have to twist (which is why they should ONLY be made from I Beam design) etc.
Yeah I know that NASCAR guys use them, but that's because they have for years and Everyone HAS to run them by the rules. You will notice that NASCAR also requires them to be I Beams.
Just not for me.

[silver69camaro]

I agree, no truck arms.

[silver69camaro]

Why does the triangulated 4-link bind? It shouldn't bind unless using rigid bushings instead of sphericals?

Thats correct. A well-designed triangulated 4-bar/link shouldn't bind until 5 or more degrees.

[Bryce]

Why does the triangulated 4-link bind? It shouldn't bind unless using rigid bushings instead of sphericals?

It wont bind during a normal roll in a turn if you run some type of swivel at both ends of the bar. Take a look at Fox and SN95 mustang rear suspension. They have lots of issues with their quadra-bind. Mostly those issues are compromises due to packaging and driver comfort.

[AMC Racer]

Thanks! Was working on a T4L design and wasn't sure if I was missing something that caused bind. Doing layouts on the different link arrangements using Solidworks, and all seem to bind in roll without some sperical joint at the ends of the links. With sphericals, the limits seem to be only the limits of the rod ends themselves and expect with bushings it is the elastic limit of the material, so maybe the 5 deg. limit is a good design choice for reasonable loads with typical rubber or urethane bushings?

Thanks!

[silver69camaro]

Thanks! Was working on a T4L design and wasn't sure if I was missing something that caused bind. Doing layouts on the different link arrangements using Solidworks, and all seem to bind in roll without some sperical joint at the ends of the links. With sphericals, the limits seem to be only the limits of the rod ends themselves and expect with bushings it is the elastic limit of the material, so maybe the 5 deg. limit is a good design choice for reasonable loads with typical rubber or urethane bushings?

Thanks!

6* is about the limit for urethane, but you could get by with more using rubber...but the body shouldn't roll more than 3 degrees anyway.

[zerotofear]

Tune me in, what's the un sprung weight of a truck arm!

[exwestracer]

Tune me in, what's the un sprung weight of a truck arm!

How about explaining your suggestion for truck arms, Mark. Sounds like you deal with them a lot there at Metalcraft...

[zerotofear]

The "Truck Arm" supension model has a pretty impressive history. Since 1963, the design has won or placed in more sanctioned performance events than other rear set-up. Contrary too popular belief, not all were NASCAR events, on asphalt, or turning left.
The design that originated from early model Chevy trucks, but doesn't lend itself to the fact that the system is simple and effective. Many jump to the conclusion that Barney Fife hides these antiqated dinosaurs in a barn in NC, but the truth is the current generation of NASCAR style truck arms are a trick piece. The system is made up of two 48" torque arms, yes, torque arms, that under extreme acceleration uses the forward weight of the car to anchor and absorb energy then transfer that energy in the form of forward bite. Under braking the arms again absorb and transfer energy thats settles the car, and systematically transfers weight on to the front suspension making the car turn better. The center pivot design perimeter allows the car roll freely , forward or back, on entry or exit, right or left. The long track bar limits rear end steer but also allows control of the effective mechanical avantage of the springs by changing the roll center height. In the 80's NASCAR shortened the wheel base , narrowed the tread width, along with areo issues, the cars were a hand full. Rule changes allowed us to explore many different rear geometrys, but the results were less than impressive, cars were out of control, and NASCAR quickly returned to the Truck Arms to assure safety. Many factory engineers have challenged the Truck Arm model but after reviewing they quickly realized that the truck arms are extremely forgiving.

[rustomatic]

I don't mean to be a dork, but grab a triangle and move it up and down on a diagonal axis (note the front fixed point). The thing changes shape, meaning with some triangulated suspension thing, you're going to multiply your spring rate at the wrong time in a turn (under compression), and your car will go skipping away like a flat rock. You'll also effectively shorten your suspension travel, which is bad for any kind of practical usage (2-3 inches means broken parts on the street, at embarrasing times). There are many good ideas surrounding the parallel leaf spring arrangement that people are forgetting here...

On the weight side of things, compare the weight of two two-inch wide, 28-inch long leafs with tube shocks to a couple of burly coilovers (with brackets and rods made of more burly material), and you get nearly nowhere. Let it flex, without body roll...

Just two cents on an issue that can pointlessly cost far more than it's worth...

[MrQuick]

I don't mean to be a dork, but grab a triangle and move it up and down on a diagonal axis (note the front fixed point). The thing changes shape, meaning with some triangulated suspension thing, you're going to multiply your spring rate at the wrong time in a turn (under compression), and your car will go skipping away like a flat rock. You'll also effectively shorten your suspension travel, which is bad for any kind of practical usage (2-3 inches means broken parts on the street, at embarrasing times). There are many good ideas surrounding the parallel leaf spring arrangement that people are forgetting here...

On the weight side of things, compare the weight of two two-inch wide, 28-inch long leafs with tube shocks to a couple of burly coilovers (with brackets and rods made of more burly material), and you get nearly nowhere. Let it flex, without body roll...

Just two cents on an issue that can pointlessly cost far more than it's worth...

I believe Don ended up with a 4 link set up.

rusty, although I love leafs, are you trying to compare the difference is the spring weights? shocks should be the same....leafs are 42 lbs each side. im sure you can do better than that.


advantage....adjustability, slight weight loss and moveable roll center height.

[AMC Racer]

Old thread, but curious on the truck arms? Stock car products lists their truck arms at 19 lbs. each at 51" long. They require a simple mounting bracket to bolt to the axle, much like a leaf spring mounting pad, a cross member up front for mounting plus panhard for lateral location. Is the unsprung weight really much more than a torque arm or other multi-link suspension? Is the binding in say a 3 degree max roll really any worse than a multi-link suspension with urethane bushings instead of heims? Understanding is the truck arms act as both a locating member and as a torsion bar or anti-roll bar. Assume the cross section is designed to suit these functions? Don't leaf springs with rubber or urethane bushings in the eyes work in a similar manner (plus act as the spring)?
Just curious as still trying to decide on rear suspension. Thanks!