radius arm vs 3link

[brooksy]

Serg's point based on reactive squat characteristics & Struths diagram can be used to illustrate it in a way ...
I know with my arm layout it has the intersecting point between the axle bushes roughly 25mm below chassis mount height. This in turns has my arms at a near neutral set-up at ride height. I was hoping to aim for this as speed was the important factor with the build. This was more important in design than clearance & the factors that Serg mentioned was the train of thought I was using.



brooksy

[TheBigBoy]

Being factory arms. I would put mine at about 3" above chassi point. I was going to get new control arms cut, but that didnt work out. So used the factory.

[80's_delirious]

Being factory arms. I would put mine at about 3" above chassi point. I was going to get new control arms cut, but that didnt work out. So used the factory.

Any clearnace issues between the arms and chassis etc?

[TheBigBoy]

None what so ever. At current full tuck its 60mm away from touching.

[80's_delirious]

Ofcourse there is always varying points. As with the superflex arms that locate the housing 25mm further forward. I did so with my stock arm mounts aswell. Meaning the axle centre isnt directly in the middle of the 2 bush's. And is closer to the front bush. Also moving them closer toward the middle of the housing made me raise them a further 10mm higher. What ever Ive done though, it was the right decission.

Here uniformed. This pic will help you understand more.

in this pic, it looks like the chassis mount is still higher than the diff centre line? this will mean that when the suspension compresses, the diff housing will still arc forward and upward. Flipped arms will also slightly increase the effective length of the radius arm IMO because it is flatter.


part of the benefit BigBoy will be seeing is basic leverage, picture the diff housing articulating, say left side radius arm end lifting 100mm, right side radius arm end dropping 100mm, in std form, the hub may lift and drop by 125mm?? (figures direct from arse OK), now by moving the radius arms in 30mm each side, the same 100mm movement at the radius arm end could see 150mm movement at the hub??? (again figures just for an example)


with what Brooksy has done, radius arms are tapered in, so like triangulated four link, they are closer to rotating around a single point at the chassis end during articulation. (draw a line through the centre line of the arms, the lines will intersect eventually)

cut two bits of cardboard, one as a wedge with the tip cut off, one as a rectangle. Hold the tip of the wedge on the table and twist the other end, now hold one end of the rectangle on the table and twist the other end. There will be a lot less resistance to the twisiting force with the wedge than with the rectangle. A narrower retangle will have less torsional rigidity than a wide one, which is why BigBoy is noticing a benefit.


Brooksy, is your rig built from scratch, or based on a production chassis?

[80's_delirious]

None what so ever. At current full tuck its 60mm away from touching.

how would clearance be if they were at standard width spacing?

[uninformed]

None what so ever. At current full tuck its 60mm away from touching.

how would clearance be if they were at standard width spacing?

maybe the question was because they are moved inboard at axle end, when at full stuff on one side during flex, would it be comming in contact with the chassis rail.......im just guessing this was the question.

Regarding Big Boy's pic, I dont think you could count that Jig as being his trucks set up, maybe, maybe not.....

Big Boy, are you saying that the axle end of the RA is about 3 inches higher than the chassis mount end? what is important to get an undertsanding in my mind is the axle end bush center height in relation to the chassis end bush center....is the axle end higher or lower ?

[80's_delirious]

None what so ever. At current full tuck its 60mm away from touching.

how would clearance be if they were at standard width spacing?

maybe the question was because they are moved inboard at axle end, when at full stuff on one side during flex, would it be comming in contact with the chassis rail.......im just guessing this was the question.

Regarding Big Boy's pic, I dont think you could count that Jig as being his trucks set up, maybe, maybe not.....

Big Boy, are you saying that the axle end of the RA is about 3 inches higher than the chassis mount end? what is important to get an undertsanding in my mind is the axle end bush center height in relation to the chassis end bush center....is the axle end higher or lower ?

I'll asume bigfella has jigged it up to get his angles etc correct??
Other flipped arms I have seen are still higher at the chassis

[brooksy]

80's_ delirious

- the build I am referring to is the Dual cab Lux I am doing for Shortman in members section.
I should get my arms back from laser cutters this week sometime. I will be away this weekend but I will be hooking in after that.



brooksy

[uninformed]

....................... Flipped arms will also slightly increase the effective length of the radius arm IMO because it is flatter.

If it is a stock housing and a stock arm AND IF it is possible to simply flip the arm and it fits without changing castor etc then nothing changes....the spring still fixes the axle housing to chassis height and the straight line distance from chassis bush to rear axle bush is the same even with a curve in the arm....thats how my mind sees it anyway hahhaha I could be blind for all I know

[TheBigBoy]

I made that jig to dial in caster perfectly and also set it up on a sliding scale. So nomatter what hieght, the housing is in the correct factory location. ie... 25mm forward at 5" like greg has designed in superflex arms. That jig is also set up for factory specs. Meaning all heights and angles you see are correct and exact same as on the truck parked on level ground. (I used laser levels to set it up, so its dead right)

[TheBigBoy]

....................... Flipped arms will also slightly increase the effective length of the radius arm IMO because it is flatter.

If it is a stock housing and a stock arm AND IF it is possible to simply flip the arm and it fits without changing castor etc then nothing changes....the spring still fixes the axle housing to chassis height and the straight line distance from chassis bush to rear axle bush is the same even with a curve in the arm....thats how my mind sees it anyway hahhaha I could be blind for all I know

Ha ha you make it sound so easy. The factory arm is only correct castor at factory height. And I have 5". I was using caster correction arms to correct the caster before I decided to do this. If I used the factory arms at that height and bolted them to the factory mounting brackets. My caster would be out by 8.8 degree negative.

Im not saying its 3" higher from top of housing to chassi location. It is what the picture shows. I was saying that if you lined up the 2 bolts on the lower arm end back to the chassi. It would be 3" high at intersection. All 3 holes on the arm dont line up.

[Struth]

So seems we can all agree, roughly.

To me then I am interested now in the gains from tapering the radius arms in at the axle vs in at the chassis.

It's apparent to me at least that the closer the RAs are together the better the wheel travel at full articulation and the worse the road handling, but I think adding roll resistance in for road use will over come that.

From memory coiled Bundy's have the arms tapered in at the axle housing too.

Also I want to get my head around any gains from having the axle RA bush line above the axle center vs below in standard trim as far as axle roll goes.

[TheBigBoy]

All I can say to that is... If the the road handling is wrong, then I dont want to be right.

But I will say, If your brave enough to cut and redo your chassi mounts back a few 100mm and get custom arms made. Thats still going to be better than what I have.

[uninformed]

im not sure what relation drawing a line between the 2 axle bush centers and projecting it back to the bush at chassis end does???

to my way of thinking it is the relation of each bush as an individual back to the chassis mount.....think about a stock arm. lowest axle bush center back to the chassis bush is the lower and the highest axle bush center back to the chassis is the upper....its just that the instant center is the chassis bush....like some guys have some seperation at the chassis end of their 3 links and some dont.

Struth, I think if you look at what guys do on say a rear 4 link or any link'd set up, where they raise the lower and upper at the axle end to get better axle roll axis on their lifted rigs.....for example, look at stock rovers, toys and nissans, I think they all have their rear trailing arms mounted below the axle center....the uppers set at x amount of seperation for axle rotation control....(forget about roll center heights for now) now I see alot of guys building custom link set ups with that lower on center line or even a touch above...not just for clearence, but to keep things flat(ish)

just some more ramblings

[Struth]

im not sure what relation drawing a line between the 2 axle bush centers and projecting it back to the bush at chassis end does???

to my way of thinking it is the relation of each bush as an individual back to the chassis mount.....think about a stock arm. lowest axle bush center back to the chassis bush is the lower and the highest axle bush center back to the chassis is the upper....its just that the instant center is the chassis bush....like some guys have some seperation at the chassis end of their 3 links and some dont.

Struth, I think if you look at what guys do on say a rear 4 link or any link'd set up, where they raise the lower and upper at the axle end to get better axle roll axis on their lifted rigs.....for example, look at stock rovers, toys and nissans, I think they all have their rear trailing arms mounted below the axle center....the uppers set at x amount of seperation for axle rotation control....(forget about roll center heights for now) now I see alot of guys building custom link set ups with that lower on center line or even a touch above...not just for clearence, but to keep things flat(ish)

just some more ramblings

Yep, I set my rear up with lower mounts below the axle centre line because to me setting it up at axle centre line or higher may allow the arms to perform an over centre lock up scenario under hi torque loads from the driveline or hitting obstacle in reverse. Which would be a pretty dramatic and unlikey occurence I guess. But with them lower than axle centre line the arms offer more resistance to axle roll and I would think squat as well.

[uninformed]

....and with a custom 4 link, by adding triangulation, you can play with axle roll axis and anti squat...RA doesnt have this luxury. There was a decussion on pirate in the merc section regarding on center/above and below... triaged and a few other tech guys chimed in...I think the outcome was it doesnt matter except for link strength.

[1MadEngineer]

Also I want to get my head around any gains from having the axle RA bush line above the axle center vs below in standard trim as far as axle roll goes.

damn, i was trying to not re-enter this discussion.
But - i am very wary of re-mounting the arms on top without upgrading them, on any vehicle that will do any serious offroading! It induces a lot of torque into the arm during impact situations. The cange in forces is very akin to changing from spring under to spring over, and the factory arms i feel are a little weak. Sure they might be fine for average joe, but you certainly wouldn't last long weekend wheeling with us...

[uninformed]

why not Greg, you have the info. Sharing it is good.

have you done any work with rover arms yet?

[1MadEngineer]

why not Greg, you have the info. Sharing it is good.

have you done any work with rover arms yet?

yep, should have my first disco set in the next 2 weeks. I got a disco for R&D just before xmas.

[Struth]

Also I want to get my head around any gains from having the axle RA bush line above the axle center vs below in standard trim as far as axle roll goes.

damn, i was trying to not re-enter this discussion.
But - i am very wary of re-mounting the arms on top without upgrading them, on any vehicle that will do any serious offroading! It induces a lot of torque into the arm during impact situations. The cange in forces is very akin to changing from spring under to spring over, and the factory arms i feel are a little weak. Sure they might be fine for average joe, but you certainly wouldn't last long weekend wheeling with us...

You have mentioned this in other threads and I agree, the factory arms are designed to work in there standard position and I can see how they may become a weak point when flipped but still expected to absorb the same forces.

But (yeah I know there's a but) in less than competition style wheeling might they be strong enough. Or is it simply too risky to expect a standard component to do it's job when inverted?

[uninformed]

why not Greg, you have the info. Sharing it is good.

have you done any work with rover arms yet?

yep, should have my first disco set in the next 2 weeks. I got a disco for R&D just before xmas.

Disco 1?
how did you find them for material type and strength?
are the superior ones made from Bisaloy?

[TheBigBoy]

I wasnt going to throw my theory's out there yet. But just decided while we are actually getting somewhere with this. Lets keep going.

[brooksy]

I too was not keen on the idea of having both axle bushes above centerline which is why I opted for bush setup either side of centre.



brooksy

[dbeverett]

This is too much drama.
I'm going 3link

[TheBigBoy]

Ha ha, we have the results though mate. Just trying to figure out why. If its a toy and not a daily driver. Go for the 3/4/5 link. But most of the tec your reading on here relates to that too.

[Struth]

This is too much drama.
I'm going 3link

oops

We were only trying to help

[dbeverett]

Haha you have, the reason I was steering towards a radius arm was the simplicity, if its as much geometry in a radius as a 3 link I'll just go a 3link, atleast there I can design it on a calculated first, build in some adjustability and throw a sway bar on if it sucks on road

[TheBigBoy]

A sway bar.. or 4

[1MadEngineer]

Haha you have, the reason I was steering towards a radius arm was the simplicity, if its as much geometry in a radius as a 3 link I'll just go a 3link, atleast there I can design it on a calculated first, build in some adjustability and throw a sway bar on if it sucks on road

a 3 link is easy as!




BUT a good 3 link is a freakin lot of hard work!! and generally will take 3-4 attempts even for someone that has done it many times before. It will also cost much more once complete and comparable to a good RA setup. ( been there done that......)