Why no Radius arm suspensions?

[Tigerstripe40]

I have been following Slee's UZJ-100 build up and have been wondering

Why aren't there more radius arm with Panhard rod suspensions being used for Coil sprung FJ40s?

It seems like it woudl be REALLY simple to set up considering the availability of premade radius arms (slees).

I want to run 37-40" tires under my FJ40 at some point and would LOVE to run it coil sprung.

 

[Mace]

radius arm suspensions are very simple. And do show up on a lot of linked rigs.

However, without doing some sort of wristed arm style design they will bind easily. And either chew up bushings or limit suspension.. There are ways around this, but a properly set up 3 link or 4 link is superior. Due to handling characteristics and usability..

 

[Isotel]

Edit: Mace Said it, Plus,

Slee's Radius arms are pricy!

Reading thru action jackson's 3 link has some good info on it,
http://www.actionjackson.com/cruiser/mods/20060110.asp

James, Glad to see your building up that Sucker, Had a Blast with you on Poison Spider, too bad my steering blew up!

 

[clownmidget]

The discussions from the 80's in favor of retaining the radius arms (and negative aspects of front linked setups) always points to the front binding as a benefit that "forces" the rear to flex more and prevents the front from unloading (like on steep climbs and sidehills). Seems like this argument gets a lot of traction and most 80's owners see a 3-link front as a liability with no redeeming qualities other than allowing it to ramp well.

I'm in the middle of 3-linking mine but am curious about how it will behave compared to the radius arm setup and am considering retaining the front springs at top and bottom as an experiment. Is that just dopey?

 

[Mace]

There is nothing fundamentally about a radius suspension that prohibits it from unloading while going uphill.. That is entirely suspension design properties..

If you have to "force" the rear to flex, the rear suspension is not set up correctly.

If you are balanced front and rear you can get a very stable, pliant suspension..

 

[Mace]

BTW, retain the springs..

 

[Tigerstripe40]

BTW, retain the springs..

Huh?

or do you mean just do a spring over and call it good?

 

[Tapage]

I always cook in my mind the radius arm idea with johnny joints at the frame .. panhard and rear for linked with panhard .

My idea it's keep it compfortable and road HW friendly ..

 

[boots4]

maybe Mace means retain the coil spring as oppose to letting it fall out when the suspension drops.

 

[Isotel]

James. it may be a good idea to do a simple Spring over in the front, then Link the rear for now.. Later down the road you can Link it when you decide you need it..

I bet a Spring over Front 40 Flexes about the same as a radius armed 80

 

[clownmidget]

I've got the bottom of the springs retained already and was thinking that retaining the tops would provide some interesting effects using the springs tension to change the way the suspension drooped. The front radius arm setup is really tough to get any more that 12" of shock travel before the eyes and brackets bind. I had the Outback arms that allowed rotation at the frame end and still couldn't fully utilze OME L shocks (just under 12" travel).

 

[camcruiser13]

soa in front flexes real nice.

remove some limitors and you can get more.


i should four link my rear

 

[Mace]

SOA 40 has more potential flex than an 80 Radius setup does.

Again, the actual type of suspension has less to do with road manners than how well the suspension is designed. I will drive my 40 comfortably on the street at 70 mph. It is more stable now than when it was a simple SOA.

I am a big fan of the 3 link w/a panhard front and a dual triangulated 4 link in the rear.


And yes, I was talking about the coil springs for retention. Capture them top and bottom. If they limit your flex, you need different springs

That is why I went 1/4 eliptic on Bob. There was not enough room with my static ride height to fit a set of coils..

 

[jeds]

Not sure if this is any help but i am in the process of coiling my bj42 check my thread . . AUSSIE BJ42 EXTRA CAB. have done alot more these are old pics heaps more done pic soon .

 

[Eskimo]

IME, radius arm suspensions have weird characteristics... one of which typically being tons of anti-dive.. the axle goes to full droop before climbing anything..

linked is mo' betta

 

[woody]

SOA front, 1/4 ellip 4-link rear....using ALL of the 14" stroke Bilsteins

 

[Cresso]

Using the "radius arm" terminology can sometimes be a little limiting. Try to think of it as a link system, with one attachment point per side on the frame and two attachment points per side on the axle. You could accomplish the same thing with four tubes and then people would call the same exact system a 4-link, albeit with the links on each side sharing a common frame-side mount. A wristed radius arm setup would then be analogous to a 3-link, with two tubes on one side and only one on the other. This is a very common setup on rockcrawling buggies, since it fits in tight packages better than a triangulated link system.

IMO, and I don't mean to attack all the excellent performance several have achieved from leaf springs, there's really only one advantage of a leaf spring system over a link system: cost. A properly designed and constructed link system will cost a LOT and will usually only return moderate gains for the investment. The leaf spring systems can be modified to be plenty for the average weekend fourwheeler, which is why you don't see more radius arm (or any link system) conversions. It's just not worth it unless you're intent on getting every last ounce of performance out of your suspension.

And a small side note: the frame-side attachment for radius arms is rarely the limiting factor. The factory post-through-bushing mount style for Ford radius arms looks like it'd bind almost immediately, but is capable of maxing out 14" shocks without breaking a sweat, assuming the arms have been wristed. I've seen a lot of folks switch to heims at the frame end and all it does is increase road vibration. The real key is to eliminate the inherent radius arm bind at the axle end. Stick with rubber bushings at the frame, wrist one radius arm, and start shopping for the longest shocks/limiting straps/brakelines you can find.

 

[Mace]

Using the "radius arm" terminology can sometimes be a little limiting. Try to think of it as a link system, with one attachment point per side on the frame and two attachment points per side on the axle. You could accomplish the same thing with four tubes and then people would call the same exact system a 4-link, albeit with the links on each side sharing a common frame-side mount. A wristed radius arm setup would then be analogous to a 3-link, with two tubes on one side and only one on the other. This is a very common setup on rockcrawling buggies, since it fits in tight packages better than a triangulated link system.

You are correct in your first description of what a Radius arm suspension is. But you cannot say that a 4 link is a radius arm and a 3 link is a "wristed" radius arm setup. The link number when referring to a 3 link or 4 link is typically represented as the # of attachment points to the frame (not including the panhard typically). So a radius arm will only have 2 "links" no matter what. Also, the # of links has nothing to do with triangulation. That is the design of the links. A 3 or 4 link can have no triangulation at all. They just need a panhard bar to locate the axle. A radius arm is not a 3 or 4 link suspension.

IMO, and I don't mean to attack all the excellent performance several have achieved from leaf springs, there's really only one advantage of a leaf spring system over a link system: cost. A properly designed and constructed link system will cost a LOT and will usually only return moderate gains for the investment. The leaf spring systems can be modified to be plenty for the average weekend fourwheeler, which is why you don't see more radius arm (or any link system) conversions. It's just not worth it unless you're intent on getting every last ounce of performance out of your suspension.

Link systems do not have to cost a ton. It all depends on how much of the work you can do yourself. If you make due with airshocks or some other spring (stock TJ comes to mind) a link suspension can be fairly affordable.. And yes, getting every ounce of suspension performance is what it is about. If it wasn't, then a Springover, spring lift or link suspensions would never have been invented..

And a small side note: the frame-side attachment for radius arms is rarely the limiting factor. The factory post-through-bushing mount style for Ford radius arms looks like it'd bind almost immediately, but is capable of maxing out 14" shocks without breaking a sweat, assuming the arms have been wristed. I've seen a lot of folks switch to heims at the frame end and all it does is increase road vibration. The real key is to eliminate the inherent radius arm bind at the axle end. Stick with rubber bushings at the frame, wrist one radius arm, and start shopping for the longest shocks/limiting straps/brakelines you can find.

Yep, the limiting factor is the bushings on the axle end. if you wrist one side you can achieve more flex. And lose a ton of road manners in the process.

 

[Cresso]

You are correct in your first description of what a Radius arm suspension is. But you cannot say that a 4 link is a radius arm and a 3 link is a "wristed" radius arm setup. The link number when referring to a 3 link or 4 link is typically represented as the # of attachment points to the frame (not including the panhard typically). So a radius arm will only have 2 "links" no matter what. Also, the # of links has nothing to do with triangulation. That is the design of the links. A 3 or 4 link can have no triangulation at all. They just need a panhard bar to locate the axle. A radius arm is not a 3 or 4 link suspension.

Stated only that way to illustrate to those who don't know how link systems are counted, since the definition of such in the fourwheeling world varies so widely. If, as I stated, the frame mount point was concurrent, it would become a single link. I mentioned nothing about triangulation changing the number of links.

A properly designed and built link system need not cost a fortune, but it's going to cost more than the leaf springs that are already on the rig. The concern here is when people cut corners to save money. Factory radius arms may have been sufficient in a stock application, but is not designed for the rigors of hardcore trails with large tires and big hp.

Wristing a radius arm is just like removing a swaybar. The effect is identical. As with swaybars, there are loads of methods out there for locking the radius arm in position for the road.

 

[bustanutley]

I'm sorry Cresso, you are adding to confusion. Mace is correct, radius arm suspension is considered a 2 link.

IME, radius arm suspensions have weird characteristics... one of which typically being tons of anti-dive.. the axle goes to full droop before climbing anything..

linked is mo' betta

I agree full heartedly with this statement. In my opinion a radius arm suspension is no upgrade from a SO front in a climbing situation without winching the front down. The only major benefit is instead of getting hung up on leaf springs you will now have link ramps . A true 3 link adds a fraction of the cost will make the suspension work so much better. It does however complicate the design process