Radius arm question.

[jerden]

Radius arm question

I have a Jeep TJ with a Rubicon Express 5.5 Long arm suspension lift. It uses front radius arms to locate the axel. So my question is what’s the down side to putting something like this on a gen I? Is it Geometry? Strength? There has to be something missing that I don’t understand. All the brackets are easy to come by to attach the upper, lower control arms and track bar to the axel. It would take minor fab work to make a lower control arm mount and track bar mount for the fame. There’s a lot of companies that make coil over brackets so that would be a no brainer. I don’t see why this can’t work but I’ve never designed a suspension either.

http://www.rubiconexpress.com/Produc...=88EF4E7243642

[Jtrux]

Let's see if I can help any.

I don't know a whole lot about these suspension systems but I do know a little which may help you. With that system you can sometimes depending on what materials are used lighten up the front end. Leaf springs are pretty heavy and if engineered correctly with the right materials the multi point suspension systems in question can be lighter.

You need three things: A track bar, which laterally locates the axle between the frame rail and the main suspension arms, whether it be two arms or four and coils, coilovers, whatever. Adding mounts to the frame for all of these things will be 100% custom and pricey depending on whose doing it. That's probably why a lot of people generally stay away from this but it has been done, i've seen it and when done correctly it's bad ass!!

The main reason I can think to avoid this is because you need to understand a little thing called anti squat. I really don't know much about this but i'll try...drag racers would probably be the best source for this. When accelerating you want the suspension to force the axle into the ground for increased tire contact, not enough anti squat and the suspension will suck the tires up...less force being applied to the tires. There is a ratio, which not everyone agrees on btw but in order to find it you need either to take some measurments from your vehicle or if you're in the planning stages draw diagrams and figure out a few measurements. You have to draw out a few lines, one through the center of gravity, then you need to find the vehicles instant centers, force vectors and using all of that you need to find out how much anti squat there is. The ratio is usually expressed in a percentage.

A few years ago I was very interested in designing something like this for my old ford truck so I didn a bunch of research but as you can tell i've forgotten it. If you do something like this, do your research, it's a lot of information.

[jerden]

Jtrux –Your point about anti squat is something I forgot to mention. Is anti squat a factor in the front end of a vehicle or just in the rear end? I would prefer to have a coil over setup in front and leave the leaf spring setup in the rear.

[Jtrux]

Originally Posted by jerden

Jtrux –Your point about anti squat is something I forgot to mention. Is anti squat a factor in the front end of a vehicle or just in the rear end? I would prefer to have a coil over setup in front and leave the leaf spring setup in the rear.

In the front of a 2wd they refer to it as anti dive and it's only under braking that it is a concern, yes you can have too much or too little anti squat in the front.

[bouncytruck]

This is all way over my head, but here's a recent post with a video of a first gen running coils.

http://67-72chevytrucks.com/vboard/s...d.php?t=304033

[sandking]

Take a look at my build thread in my signature.....
A little late for me, but I did some research. As grendel and Rokcrln mentioned, radius arms will bind in articulation. Castor is also affected which makes for steering issues.
As these two will tell me "We told you so..." lol I will be changing my front end to parallel/equal length (I dont have the room for triangulated)4-link with a panhard. If done right, it will have no change in caster and will articulate without any binding.
I mocked up these arms, and found out the hard way that this is not what I want. It may be good for some, but not for me and what I am building.

[Jtrux]

Originally Posted by sandking

Take a look at my build thread in my signature.....
A little late for me, but I did some research. As grendel and Rokcrln mentioned, radius arms will bind in articulation. Castor is also affected which makes for steering issues.
As these two will tell me "We told you so..." lol I will be changing my front end to parallel/equal length (I dont have the room for triangulated)4-link with a panhard. If done right, it will have no change in caster and will articulate without any binding.
I mocked up these arms, and found out the hard way that this is not what I want. It may be good for some, but not for me and what I am building.

I would definitely ask Sandking more questions, it looks like he's had a lot more experience with it.

[jerden]

I've abused the hell out of the Jeep at Pismo in the dunes and the suspension works great. It jumps really well but with the short wheel base the whoops eat it alive! I was wanting a simple solution to a quality suspension. But without a lot of trial and error or a huge wallet for something like http://www.blitzkriegoffroad.com/?ac...t&id=18&pid=70 is offering it doesn't sound good. So if I were to stay with leaf springs up front are 52's the way to go for an all around wheeler on 38's? I'm thinking I may need 52's up front with a 4" lift for a total of 8"s. Then I can do a shackle flip in the rear with a 4" lift spring. It needs to be able to be driven on the street, play in the dunes, hit a trail here and there and pound a mud hole.

[Jtrux]

Originally Posted by jerden

I've abused the hell out of the Jeep at Pismo in the dunes and the suspension works great. It jumps really well but with the short wheel base the whoops eat it alive! I was wanting a simple solution to a quality suspension. But without a lot of trial and error or a huge wallet for something like http://www.blitzkriegoffroad.com/?ac...t&id=18&pid=70 is offering it doesn't sound good. So if I were to stay with leaf springs up front are 52's the way to go for an all around wheeler on 38's? I'm thinking I may need 52's up front with a 4" lift for a total of 8"s. Then I can do a shackle flip in the rear with a 4" lift spring. It needs to be able to be driven on the street, play in the dunes, hit a trail here and there and pound a mud hole.

Everything you would ever need here...

http://www.diy4x.com/suspension.htm

At the top is the 1st gen flip and switch and then if you scroll down you get to the 52 inch spring hangers for 1st gen's as well.

I wouldn't lift it more than 6 inches, preferably 4. If it's a wheeler start cutting fenders, if it's for looks, then jack it up. I've seen a couple 1st gen's with 6 inch lift and 35's and it's pretty tall, taller than i'd want on the trails. 8 inch and 38's would be way too much in my opinion.

The 52 inch spring kit offered by DIY is bad ass, i'd do that without a doubt and also the shackle flip with longer shackles in the back and maybe some zero rates to re-center the rear axle.

Oh and about that 72 blazer that you linked to, WOW! That's pretty stupid expensive though.

[sandking]

Yeah, the Blitz Blazer works pretty good and has been around for years, but at $9000 just for radius arms and a simple engine cage..........no thanks. For less then $1000, you can have a good, reliable, strong linked front end that will be street, dunes and crawl friendly.

[Jtrux]

Originally Posted by sandking

Yeah, the Blitz Blazer works pretty good and has been around for years, but at $9000 just for radius arms and a simple engine cage..........no thanks. For less then $1000, you can have a good, reliable, strong linked front end that will be street, dunes and crawl friendly.

Yeah I think you're just buying the name, crazy.

[sandking]

Not too long ago, it was only $6900, now its $2000 more.......The kit works good, just cant justify the cost.