Truckarms...again How can we fix them?

[dontlifttoshift]

I'm new. I have searched. I have read every thread that pertained to truck arms and even skimmed over some of the related drama. Here is what I learned:

Inherent bind, the whole system is in a bind. Depends on what side you stand on I guess it could be good (no arb) or bad....duh, bind is bad.

Heavy unsprung weight - self explanatory, it's like having an extra 9" pumpkin along for the ride

Packaging - opinions vary, on some vehicles it isn't a big deal, like the '48 chevy pickup I had a few years back.

I have work arounds for the three things listed above and consider those problems solved. So what I really want to know, from the guys that know, is what is wrong with the geometry? My priorities are comfort (I drive) and autocrossing and it seems to me that geometrically this suspension is well equipped for those two things.

FWIW right now rear roll center is 15" off of the ground and antisquat numbers are a theoretical 90%, sorry best guesstimate. The car weighs about 2,600 hundred punds with me in it if that makes a difference. That is about as technical as I can get right now, I don't have any real measurements until I scale the car and blow it apart for the winter.

Oh, thanks for not blasting me too bad

Donny

[MonzaRacer]

So if you have bind in a truck arm set up install johnny joints in the front pivot points. then reduced bind, the bind is based over several feet in a truck arm set up and is negligible in my opinion. as for weight then you either need to redesign the arms to weigh less either in materials or actual design. or install a different suspension.

[ArtosDracon]

I like truck-arm suspensions. I've considered it for my blazer. Just use a spherical end on the front, and modify the design\materials slightly and there is nothing wrong with it.

[monteboy84]

Turn it into a Torque Arm style suspension and it should work fine

-matt

[Mingus]

I know Hotrods To Hell have a "correction" kit for stock 60's GM truckarms. I don't know if it's good, bad or otherwise I just remember seeing it advertised somewhere.

[Payton King]

He is running a truck arm and his car is quick around the big track and autocross.

[dontlifttoshift]

He is running a truck arm and his car is quick around the big track and autocross.

Who is?



I have got the bind problem solved. After reading my post I guess I should have been clearer. What is the best geoemetry for a truckarm style setup.

Please no "just turn it into a three link, 4link, torque arm, IRS." that doesn't hlep me do what I am trying to do. Us street rod types have been using this setup for 25 years or so, i just don't think there was any science behind their application....it was all based on simplicity and packaging......I am looking to optimize it.

Thanks
Donny

[John Wright]

Who is?

Donny,
Here ya go:
https://www.pro-touring.com/forum/sh...ad.php?t=38420

[dontlifttoshift]

DSE swivel link in the front, I wittled some delrin bushings for the front but I am going back to rubber this winter for NVH purposes. In the back is a left hand/right hand threaded adjuster for wheelbase and pinion angle adjustments and a 1/2" clevis bolts it to the rear axle with shoulder bolts.

I hope this helps.

[dontlifttoshift]

Donny,
Here ya go:
https://www.pro-touring.com/forum/sh...ad.php?t=38420

Thanks I didn't see that one, I will have to wait for lunch to read that one though.

[Bryce]

Those look like longer ladder bars. I guess they would work the same. and lighter than a normal truck arm. I would say for geometry it would be similar to other systems. Road race application would be 50-60% antisquat. IC is fixed at the front pivot points. Maybe run a watts link and a swaybar for tunning. i know typically you would adjust the height of the panhard bar, to adjust roll center and stiffen or loosen the rear end. Also what is your CG height? That may determine what kind of lateral locator you use. You might need something really low.

[monteboy84]

Any reason for not running spherical rod ends/bushings at all 6 points? I think if you went that route it would alleviate any bind issues associated with other applications, where the truckarms are bolted rigid to the housing, as yours will be.

-matt

[DynoDon]

Who is?



I have got the bind problem solved. After reading my post I guess I should have been clearer. What is the best geoemetry for a truckarm style setup.

Please no "just turn it into a three link, 4link, torque arm, IRS." that doesn't hlep me do what I am trying to do. Us street rod types have been using this setup for 25 years or so, i just don't think there was any science behind their application....it was all based on simplicity and packaging......I am looking to optimize it.

Thanks
Donny

So are you running Truck Arms or Triangulated Ladder bars?
I have noticed when setting up Street Rods with triangulated ladder bars, that if I use rod ends instead of bushings in the front location, that the cars get a bit of a rocking motion side to side, especially without a sway bar, which many street rod guys do not want for aesthetics.

[dontlifttoshift]

Those look like longer ladder bars. I guess they would work the same. and lighter than a normal truck arm. I would say for geometry it would be similar to other systems. Road race application would be 50-60% antisquat. IC is fixed at the front pivot points. Maybe run a watts link and a swaybar for tunning. i know typically you would adjust the height of the panhard bar, to adjust roll center and stiffen or loosen the rear end. Also what is your CG height? That may determine what kind of lateral locator you use. You might need something really low.

Why such a low value for anti-squat? Isn't traction king?

Is there a significant advantage with the watts vs. a panhard in reagrds to truck arm geometry or is the difference the same for all.

Sway bar would tune better than changing roll centers, correct? Or does it take a combination of both.

CG is estimated at 20" to 22". The car is near neutral front to rear, actually a tad heavy on the rear.....I don't have the actual numbers in front of me.

Thanks, this is what I was looking for and is what is lacking from most forums I hang out at.

[dontlifttoshift]

[

QUOTE=DynoDon;726296]So are you running Truck Arms or Triangulated Ladder bars?

Forgive me, I don't see a difference....geometrically speaking. I am running ladder bars.

I have noticed when setting up Street Rods with triangulated ladder bars, that if I use rod ends instead of bushings in the front location, that the cars get a bit of a rocking motion side to side, especially without a sway bar, which many street rod guys do not want for aesthetics.

Isn't that what we want, bind free articulation?

[dontlifttoshift]

Any reason for not running spherical rod ends/bushings at all 6 points? I think if you went that route it would alleviate any bind issues associated with other applications, where the truckarms are bolted rigid to the housing, as yours will be.

-matt

Never really thought about it. From my limited experience, the swivels at the front cure the bind issues.

[DynoDon]

[

Forgive me, I don't see a difference....geometrically speaking. I am running ladder bars.
Not sure if there is really any difference in the geometry, but they are two different things physically and I just wanted to make sure what you were working with


Isn't that what we want, bind free articulation?

According to my NASCAR sources, the truck arm design is never bind free, by design. The arms move in two different arcs and that causes a twisting motion in the axle that the truck arm handles by twisting itself. It is why the arms are made of an I Beam section, not square or round tubing*. By design the truck arm suspension acts like a big sway bar. They use truck arms of different section area to change rear roll resistance and use different front bushings or sometimes mono balls to also change the roll stiffness.
Ladder bars offer almost no resistance to twist and therefore require sway bars and stiff front bushings to help control rear body boll.
* There are some companies making "Street" oriented truck arms from square, rectangular, and or round tubing and the roll resistance of these is very high and they are susceptible to cracking over time.
At least this is how it has been explained to me by a NASCAR suspension expert.

[dontlifttoshift]

Yeah, we are on the same page. We've done a bunch of cars with the the Pete and jakes type ladder bars and for a cruiser they work great.

Instead of twisting I beams we have a smooth radial motion with the swivel link at the front of the ladder bar.....about as bind free as you can get with this set up.

[Bryce]

Why such a low value for anti-squat? Isn't traction king?

Yes, but you are not starting from a standstill at all times. You dont need that much antisquat at 30mph as you need at 0 mph. The more A/S the more brake hop.

Is there a significant advantage with the watts vs. a panhard in reagrds to truck arm geometry or is the difference the same for all.

I think Truck Arms will react the same as other suspensions with a panhard and watts. Watts is less bind and less, almost zero lateral movement.

Sway bar would tune better than changing roll centers, correct? Or does it take a combination of both.

The torque arm that cause body roll is the lenght between RC and CG. The sway bar counteracts that torque arm. The lower the RC the more body roll you could experience due to the longer torque arm. You would increase your sway bar stiffness to counteract the increase in body roll.

CG is estimated at 20" to 22". The car is near neutral front to rear, actually a tad heavy on the rear.....I don't have the actual numbers in front of me.

Thanks, this is what I was looking for and is what is lacking from most forums I hang out at.

[silver69camaro]

Any reason for not running spherical rod ends/bushings at all 6 points? I think if you went that route it would alleviate any bind issues associated with other applications, where the truckarms are bolted rigid to the housing, as yours will be.

-matt

I'd avoid sphericals if possible due to NVH issues. They can be awful on the street.