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How do radius arms work?
https://auszookers.com/forum/viewtopic.php?f=5&t=47351		 Page 1 of 3
Author:  Gwagensteve [ Sun Aug 10, 2014 6:14 pm ]
Post subject:  How do radius arms work?
I was browsing though PaulW's build thread (which is a really cool tread BTW) and came across this photo:


Image

And it really puzzled me.

Radius arms rely in deformation of the bush vertically (or more specifically, radially around the axis of the chassis mounting bracket) in order to provide articulation. If anyone doubts this, they should flex their radius arm car with one axle end bolt removed.

However, this arm design doesn't permit deformation of the bush, as it's an articulation joint. I can only assume that the only way this arm design permits articulation is by flex in the axle housing or by bending the arm.

Can anyone shed any light on this? Surely the manufacturers of the arms can't have overlooked this?

Steve.
Author:  bangn [ Sun Aug 10, 2014 6:23 pm ]
Post subject:  Re: How do radius arms work?
they correct the angle of the diff to maintain correct shaft and wheel angle.. Thats why caster correction bushes have been fitted in the lower arm. Also reduces wheel shimmy (shopping wheel effect) The above shaft looks to be designed for a more aggressive lift and so it already counteracts the angle to be flat in its design

as you lift the car (or the arms drop lower) the diff angle changes. Plus the lower arms are shit. Bend like bananas.
Author:  SierraDan [ Sun Aug 10, 2014 6:24 pm ]
Post subject:  Re: How do radius arms work?
I think you have misunderstood the questions bangn
Author:  Gwagensteve [ Sun Aug 10, 2014 6:42 pm ]
Post subject:  Re: How do radius arms work?
I understand the problems they are supposed to correct, but I don't understand how these arms permit articulation.
Author:  BertZook [ Sun Aug 10, 2014 7:56 pm ]
Post subject:  Re: How do radius arms work?
so in what way the new arms differ from the originals?. apart of correcting the caster in bigger lifts
Author:  Gwagensteve [ Sun Aug 10, 2014 8:00 pm ]
Post subject:  Re: How do radius arms work?
There's no way the new bushes can deflect vertically.

I'll admit that urethane bushes with caster correction also permit little deflection compared to stock rubber bushes, but "little" is a lot more than none.

Steve.
Author:  BertZook [ Sun Aug 10, 2014 8:04 pm ]
Post subject:  Re: How do radius arms work?
oh ok, I tough the arm itself was the question, not the bushes.

He decided to put those bushes in. The arms won't come, and are not being offered with those bushes.
Author:  Gwagensteve [ Sun Aug 10, 2014 8:06 pm ]
Post subject:  Re: How do radius arms work?
IMHO then they need stock rubber. If this flexes at all it's because something is bending that shouldn't.
Author:  zukenutter [ Sun Aug 10, 2014 8:12 pm ]
Post subject:  Re: How do radius arms work?
So is this about the arms or the bushes?
Author:  sideways [ Sun Aug 10, 2014 8:16 pm ]
Post subject:  Re: How do radius arms work?
BertZook wrote:
so in what way the new arms differ from the originals?. apart of correcting the caster in bigger lifts


They have spherical joints in place of the original rubber/poly bushes. These don't allow for any deflection (which is what radius arms require to flex) but they can rotate to allow a greater difference in angles than rubber or poly bushes. This is great in something like a 4 link where the deflection isn't required but high rotation angles are beneficial (for flex) which is why rock crawlers and so on (which generally don't have radius arms) run them. Also, because they don't have any deflection they make the vehicle feel "tighter", hence their extensive use in racing/high performance vehicles.

As Steve says, the only way that can be flexing is if the housing/arms are bending or if the joints are rubbish.

EDIT: beaten. ZN, it's about the bushes, not the arms.
Author:  3cyl [ Sun Aug 10, 2014 8:31 pm ]
Post subject:  Re: How do radius arms work?
I think the arm will tear where the webbing attaches to the tube, then it'll articulate.
Author:  Gwagensteve [ Sun Aug 10, 2014 8:32 pm ]
Post subject:  Re: How do radius arms work?
I reckon the axle brackets will fail first.
Author:  zukenutter [ Sun Aug 10, 2014 8:32 pm ]
Post subject:  Re: How do radius arms work?
Yep cool, and I've just clicked to the issue here.

Am I correct in assuming that installing these joints at the chassis end of the arm would work ok because it's just a single eye?
Author:  watermouse [ Sun Aug 10, 2014 8:38 pm ]
Post subject:  Re: How do radius arms work?
If the front bushes are steel, as they appear to be, then all the flex will occur in the chassis end bush. The arm will stay in a vertical plane relative to the diff. In a normal Jimny setup the chassis end bush flexes radially about half the angle the diff is at while the front two bushes would flex the other half.
note: In Paul's photo there is no bush yet installed in the chassis end of the aftermarket arm.
Agreed its not ideal but this setup would give better castor angle control under braking as the diff cant twist axially under the car when stopping, there are no bushes to deform.
Also the aftermarket arm being made from round tube would transfer the extra torsion load to the chassis end bush much more effectively than the cast i-beam stock design.

In any case, its not uncommon for Jimny's to snap the diff or chassis brackets off from over articulation.
IMO a pin end perpendicular to the diff (like Landrover Defender and others) or articulating joint at the chassis end would permit the use of solid bushes on the diff end and not restrict diff articulation to the maximum of what any bush can handle.
Author:  Gwagensteve [ Sun Aug 10, 2014 8:42 pm ]
Post subject:  Re: How do radius arms work?
I 100% disagree watermouse. Regardless of the bush used at the chassis end, four solid bushes at the axle end will restrict flex to the amount the axlehousing or arm can flex.
Author:  watermouse [ Sun Aug 10, 2014 8:47 pm ]
Post subject:  Re: How do radius arms work?
sideways wrote:
BertZook wrote:
so in what way the new arms differ from the originals?. apart of correcting the caster in bigger lifts


They have spherical joints in place of the original rubber/poly bushes.


I was bit slow on that last post :?

So the front "bushes" are spherical joints with steel retainers on the outside? So it can still roll/twist to some degree at the front end?



Yes I agree with you Steve that it would reduce flex but only to the degree that the rear most bush can deform. then the brackets load up and snap.

Unless as sideways states that the front bushes are in fact spherical joints than can allow some roll but less deformation. It is not entirely clear. Someone should ask Paulw.
Author:  Gwagensteve [ Sun Aug 10, 2014 8:52 pm ]
Post subject:  Re: How do radius arms work?
They're spherical joints that should allow zero deformation. I imagine less than 12mm of deflection would be possible at the chassis end. I suspect that would allow about 50mm of articulation, if that, before something starts to be overloaded.
Author:  SierraDan [ Sun Aug 10, 2014 8:53 pm ]
Post subject:  Re: How do radius arms work?
They are a steel spherical bearing with misalignment spacers built in. They run in two hard poly halves encased in a steel sleeve.
Author:  sideways [ Sun Aug 10, 2014 8:54 pm ]
Post subject:  Re: How do radius arms work?
Excluding the flex from the bending housing, arms ect the diff can only move up and down.

In a perfect world with no bendy parts or play/deflection in the joints, essentially the suspension setup is no longer radius arms but a swing arm, like you'd find in the rear of most quad bikes. There's no allowance for articulation. The arms might as well be welded to the diff housing and (in this perfect world) you could throw the panhard bar away.
Author:  31zook [ Sun Aug 10, 2014 8:55 pm ]
Post subject:  Re: How do radius arms work?
Looks like its going to be a stiff ride... weird, keen to hear what paulw has to say about them
Author:  Gwagensteve [ Sun Aug 10, 2014 9:01 pm ]
Post subject:  Re: How do radius arms work?
That's my take on it sideways
Author:  watermouse [ Sun Aug 10, 2014 9:18 pm ]
Post subject:  Re: How do radius arms work?
Aahaa.......
Just clicked :oops:
I am not on the ball tonight. I was looking at it as a single sided system and was ignoring what the other arm did. I can now see how this won't work if the front bushes can't deform.

Please, everybody, ignore my poor attempts at an explanation.
Author:  alien [ Sun Aug 10, 2014 11:20 pm ]
Post subject:  Re: How do radius arms work?
so what all y'all are saying is that he should fit some:
Image

right?
Author:  atari4x4 [ Sun Aug 10, 2014 11:52 pm ]
Post subject:  Re: How do radius arms work?
would they be better off in the chassis end?
Author:  fordem [ Mon Aug 11, 2014 2:15 am ]
Post subject:  Re: How do radius arms work?
Gwagensteve wrote:
Surely the manufacturers of the arms can't have overlooked this?

Steve.


Don't underestimate this as a possibility - not all of the manufacturers out there have properly designed (or even necessary) products.

There is a Malaysian "chassis tuning specialist" with a wide range of products, including a tubular underbody brace for a Mitsubishi - this brace is intended to stiffen the front cross member, presumably to reduce flex from the forces exerted by the lower control arms (it's a traditional coil over strut MacPherson strut design).

In my opinion (and I'm no engineer) the original cross member - which also cradles & supports the engine, and is used as the front central jacking point - is way stronger than the brace, and the brace is totally unnecessary.

If any one is curious enough I can post a picture taken from the manufacturer's website and a link to the original location
Author:  Jezza86 [ Mon Aug 11, 2014 6:20 am ]
Post subject:  Re: How do radius arms work?
These were on the ebay thread a while back
My understandind was up/down movement in the urathane took out some vibration and the bearing inner race could rotate like dis providing less resistance and relied much more heavier on the panhard. I thought the outer bearing case was spherical to encapsulate the inner raceImage
Author:  zukenutter [ Mon Aug 11, 2014 8:01 am ]
Post subject:  Re: How do radius arms work?
Steve, am I understanding the issue correctly?

Image
Author:  droverdave [ Mon Aug 11, 2014 8:14 am ]
Post subject:  Re: How do radius arms work?
I think we need more details on what exactly those steel looking joints are where bushes normally go. Hard to tell what they are from those photos.

If they are indeed solid, then i agree that its worse than stock rubber ones.

You sure its not something like this?

Though im not familiar with the differential end, but if they flex too much does the arm itself hit on the bracket? (if that makes sense)

edit: actaully thinking about it all again, since there are two bushes, these type below wont help at all as there will be no sideways movement of the arm itself. The only way to get the flex you want is to have more soft bushing, not less like the original photo shows.

Image
Author:  Paulw [ Mon Aug 11, 2014 8:31 am ]
Post subject:  Re: How do radius arms work?
:oops: Soo in everyone's opinion would it be better to have rubber bushes on the diff end and these joints on the chassis end?

I was just trying stuff out :lol:
Author:  monley [ Mon Aug 11, 2014 9:03 am ]
Post subject:  Re: How do radius arms work?
http://www.lowrangeoffroad.com/builderp ... -9112.html

These are the same joints in run in my ute at the chassis end. They offer good movement in my application and it's a common choice for jeep to run these at the chassis end as well from when I was reading about them before I got them. I was also going to run these in my jimny when I had it as my middle bush keep tearing and was going to replace with a johnny joint but only the middle link. I think It might of even been Steve that suggested it to...

Good for leaf springs to :?

http://www.lowrangeoffroad.com/builderp ... ounts.html

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