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Antidive/Antisquat: how much do I want?


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when under acceleration, high anti dive in the front is like low anti squat in the rear. As the links are now on the other side of the axle housing, but both front and rear housings are rotating in the sdame direction. So it appears to me that high anti dive in the front will suck the front down rather than jack it up…… This came up on pirate not long ago in a thread I started about anti dive. I am more concerned with it at speed for braking though.

I also pondered the question of how the 2 ends react with each other as they way the link calculators looks at them is individually, almosty as if only 2wd…..

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I had a visit this morning from a journalist/photographer and long time offroad vehicle builder, who want to do a series of stories on Old School 4x4 enthusiasts who build their own stuff, as opposed to handing over a blank cheque to the ARB Corp for lots of shiney bells and whistles.Anyway, they asked to see Wildfing up on the articulation ramp to get a clearer view of the suspension ,transmission and portal axles. we got around to discussing Antisquat and why WildFing doesn't play by the rules. Now these guys are no dills, one in particular is at least my equal regards technical experience,It was surreal that the answer came to the three of us simultaneously. Looking at the chassis attachment point of the rear One Link showed that it was close to mid wheel base and as near as dammit to the for/aft location of the Centre of gravity. What that means is that the upward push from the end of the OneLink is fighting close to the whole of the trucks unsprung mass. Now WildFing is no lightweight at 2200KG's.Subtract say 750kg for axle assemblies, wheels /tyres and that leaves around 1450 kg or 3190 lbs of unsprung mass that the One link is trying to push upwards against. The effective length of my One Link is 4ft. If I was dragging an extremely load or climbing a very steep gradient in just rear wheel drive and was able to generate 8000 lb ft of torque at the rear axles, the lifting force at the end of the One Link would be 2000lbs. I don't think that 2000 lbs of upforce is going to make much impression on 3190 lbs of downforce, and that is why Wildfing doesn't jack its bum up when climbing.BTW, 8000lb ft of torque at the axles is well in excess of what Rover type diff/axles could cope with. Even a standard 30 spline Dana 60 is rated at only 6000lb ft.Also, very little serious 4wding is done in just rear wheel drive, and the 'squatting' effect of radius arm. OneLink or 3 link front end would also apply a downforce close to the for/aft centre of gravity position as well, which should probably further oppose that 2000lbs of upforce from the rear One Link.

Bill, can we get a copy of these mags, when they come out?

Daan

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Just back to the thread been contemplating what to do with the front of my toy.... My whole idea with the reverse rate AS for the rear was to improve it when climbing... with the front end anti dive, do I have the same need, for me with an offroad toy (trailer queen)

when I need brakes Im not going to be going fast so its not going to be a long sustained brake, when Im really wanting them to work is most likely when Im pointing down hill... so given this a standard rate with a moderately high rate to start or at rest......

so whats your thinking on this ?

When I originally replaced the leaf springs on WildFing, I basically copied the RangeRover/Defender Arrangement of Radius arms and outboard coils. The difference in front end climbing ability was amazing, both from the driver seat and for outside observers. Instead of the front sprung mass rising and losing traction as it did on leafs,it pulled down with the RA's. Whilst antidive characteristics may not be so important for us, the opposite affect when the front axle is pulling is front end squat. Once again, as with rear antisquat, loss of traction will relax this downward force, so the front shocks need to be good to prevent bounce.

A similar leading arm affect can be had with leaf springs by reversing the shackle location as on LandCruisers, Jeeps etc. They climb knarly stuff so much better than Series Landrovers, and don't hop, skip and buck when crawling over rocks, steps and logs. The front propshaft slip joint also lasts 3 times longer. The perceived higher incidence of leaf spring breakage with this type of shackle arrangement is only true for distance driving on high speed corrugations. LandRovers well known front axle tramp

if not fitted with a tramp bar breaks more springs in extreme terrain than Toyotas and Jeeps etc do.

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Bill, can we get a copy of these mags, when they come out?

Daan

Yesterday was just a preliminary discussion to outline the interview and photo shoot that is scheduled concurrently with the Suzuki 4wd club gathering on my block at the end of the month Daan. Apparently the articles will focus more on individuals than the actual vehicles, which is fine, but I hate having my photo taken in case Interpol is watching Lol. The name of the magazine escapes me now, but no doubt when it happens there would be a complimentary magazine or 3 .

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A similar leading arm affect can be had with leaf springs by reversing the shackle location as on LandCruisers, Jeeps etc. They climb knarly stuff so much better than Series Landrovers, and don't hop, skip and buck when crawling over rocks, steps and logs. The front propshaft slip joint also lasts 3 times longer.

Why are rear shackle kits available for Jeeps then?

Thinking in my project...in some months I will have a Disco 200, with rear ARB and +2" suspensión with rear cranked triling arms and dislocation cones.

The terrain we have here is basically mud with deep ruts from forest machinery. Good suspensión travel is needed for crossing diagonally those deep ruts.

Rear suspensión is good with standard setup, but front radius arms are not that flexy.

My Disco will have slightly more rear AS than standard (suspensión lift + crancked arms = more angle = more AS).

The front is not defined yet. I want to use standard radius arms for easier paperwork/test/calculations for making it road legal. It seems that, in standard form, they are too short (too much AD?) for beeing used for a Unilink. That was the reason for starting this thread, as I don´t know if it will be good making them longer.

What will be the expected behaviour with slightly more AS and slightly less AD tan standard?

Driveline will be part of the game. I will like to build a double low box combo that will be longer. That will mean also longer front propshaft, and some longer front arms will help the slip joint.

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"Why are rear shackle kits available for Jeeps then ?"

Because there is a market out there to the ill informed for anything! You don't think for a second that LandRover got anything right with series vehicles do you? Actually they did, back in 1948 when they had the shackles up front. Having owned 2 80" landrovers together, one 1948 model and a 1951 model with shackles at the rear, I can attest to the superior difficult terrain performance of the earlier vehicle. Mind you neither of them even came close to the performance of an M38 WW2 Jeep or Dodge Weapons Carrier when the going got knarly.Flexible chassis on those two examples kept the wheels planted long after the 80" ran out of articulation.

Just save yourself a ton of work and hassle with your authorities, and just pull the front bolt from your left hand radius arm when you want more articulation. It works good enough in the terrain you describe. Just make sure your brake hoses are long enough.

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So pirate is worth watching lol I gave up on it because of all the muppets who like to parrot carp they dont understand and that includes some of the vendors. I found most of those that are worth listening to are also on the desert forums....

Interesting that you mention high anti-dive pulling the front down.... I bounced some ideas off Triaged a few yrs ago to do with forces on the front axle

For me with a toy that is not intended for fast stuff, about the fastest I'll be going is 60km on gravel roads.... grip wise Im never going to have enough to risk brake hop so it maybe worth having a play with high AD

Bill you mention radius arms pulling down, from playing round on spreedsheets I've found they "ramp" the AD quickly, I'd have to really play with a three link to get that, is that what causes it ....or is it due to the axle torque on the links, being that radius arms are one of the few link systems that is solid to the axle.... to me the torque makes more sence.... if that is the case then the 3 link wouldnt do the same ?

Damm I didnt want to go the path of a 1 link hmmmm

going to see if I can find the Pirate thread

for T's post

rear shackles on the front axle give better steering, your drag link is normally in the front so less movement due to being closer to the spring eyes, and this movement is generally bump steer the worst one for steering.... the kits are for muppets who dont understand suspension and think that because some hilux has big flex this is what they need, they dont fit them for the real gain lol to me I think land rover did the right thing if it road going then steering is more important than climbing ability remember most drivers dont know how to drive to the conditions and the vehicle

You want better flex from radius arms consider a "wristed radius arm" this will take the bind out of your radius arms and can be done easily... question is if it is the torque lock out of the links that pulls the front down then this mod will cause the truck to twist

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"Why are rear shackle kits available for Jeeps then ?"

Because there is a market out there to the ill informed for anything!

I allways thought that rear shackles were better just because they gave better angle. Poor me...

Just save yourself a ton of work and hassle with your authorities, and just pull the front bolt from your left hand radius arm when you want more articulation. It works good enough in the terrain you describe. Just make sure your brake hoses are long enough.

That particular Disco is equipped with extra long hoses. I thought of taking away one bolt after seeing this picture...

8qr6.jpg

You want better flex from radius arms consider a "wristed radius arm" this will take the bind out of your radius arms and can be done easily...

Will investigate that...sounds interesting.

EDIT: after a quick search I have found some pics.

Ford F-150

d44%20072s.jpg

(look that shock...!)

I heard of them some years ago, beeing called "hinged" radius arms

hinge1.jpg

hinge4.jpg

It does not seem a popular setup, and some comercial projects were not materializated.

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Not very practical once the hole is full of mud and won't line up to get the pin back in!

I have a hybrid with a hinged RA (not my work) and it has never been a problem lining the pin back up. And despite the criticism often aimed at this mod, I can't make the hybrid do anything silly on offcambers that it doesn't do with the pin fitted.

But that is an option that O'Teunico's Spanish authorities would probably condemn.Removing the L/H/Front radius arm bolt before entering his forest is much more discrete. With either method, firmer eurethane bushings at the axle would give better control of torque reaction without reducing articulation.

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I guess then, that the leaf springs + panhard setups were only found on vehicles with front shackles?

My brain hurts with most of the above, I think I picked that bit out right though :)

I found uniformed's thread on pirate and read through it... and I have a headache now lol

Bowie there is a bit more to it than just that, the length thing applies, short spring / shackles less movement, long springs with long shackles add into this lots of bow in the springs you are getting a fair amount of distance between your axle and chassis I have build trucks with rear shackles that Ive fitted panhards to

Just so I dont loose those who are following along with this thread

In this pirate thread one of the members set his truck up with 200% AD, and -25% AS I can understand his motivation to try the extremes, I consider AS & AD to work similar to a sin curve in its performance (this is an interpretation)

Now he found the front end tended to pull down in acceleration the consensus was it is due to the links for the front axle being on the rear of the front housing as the front axle rotates forward.... so the forces are backward

Im having a hard time sorting this out in my head and this headache isnt helping..... what Im trying to do is work out if there is a bonus from this reaction for a radius arm style (1 link) compared to a floating link setup like a 3 link... if there is how can we use it

right Im going to take some painkillers and go lie down

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I found uniformed's thread on pirate and read through it... and I have a headache now lol

Bowie there is a bit more to it than just that, the length thing applies, short spring / shackles less movement, long springs with long shackles add into this lots of bow in the springs you are getting a fair amount of distance between your axle and chassis I have build trucks with rear shackles that Ive fitted panhards to

Just so I dont loose those who are following along with this thread

In this pirate thread one of the members set his truck up with 200% AD, and -25% AS I can understand his motivation to try the extremes, I consider AS & AD to work similar to a sin curve in its performance (this is an interpretation)

Now he found the front end tended to pull down in acceleration the consensus was it is due to the links for the front axle being on the rear of the front housing as the front axle rotates forward.... so the forces are backward

Im having a hard time sorting this out in my head and this headache isnt helping..... what Im trying to do is work out if there is a bonus from this reaction for a radius arm style (1 link) compared to a floating link setup like a 3 link... if there is how can we use it

right Im going to take some painkillers and go lie down

The front axle rotates (rocks) backwards when driving forward and rocks forward when in reverse gear, so when driving forward the radius arms, One Link, or 3 link, if the upper and lower links projected lines converge to an instant centre will produce a downforce at the front of the chassis.

I could be very wrong about the following, but although Pirate has branched out to cover other types of terrain, it is advertised predominently as a rock crawling forum, and because of the very high traction rock they tend to drive on, they are pushing the upper limits of gradient angles that are actually climbable, so there would be very little traction at the front axle to make the links pull down anyway. So they focus on the rear axle to make its behaviour consistant between the two extremes of high traction to no traction to prevent axle hop. We, who mainly operate in softer, looser terrain, can probably exploit antisquat forces to push the rear tyres down more firmly to gain extra bite.

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yes sorry about that thread "De Ranged" of coarse it went pair shaped when I got confused by "loose" terminology and their use of IFS/IRS pictures that did not relate to Solid axle. I also started the thread from a braking perspective, but they dont care about that and seem fixated on the going forward stuff….Still some good points were made.

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The front axle rotates (rocks) backwards when driving forward and rocks forward when in reverse gear, so when driving forward the radius arms, One Link, or 3 link, if the upper and lower links projected lines converge to an instant centre will produce a downforce at the front of the chassis.

Yea thats the obvious one equal and opposite... wheel goes forward housing has to rotate back to resist .... just on a tangent this is an interesting one to try and take advantage of this, you want your chassis anchor points to be as close to the front of the vehicle as possible

No what I was thinking of was

First does AD really accentuate this effect so far we have one person who has anecdotal evidence.... but by my understanding of the forces is that AS or its reverse AD transfer force from the springs to the links, the greater the % the greater the amount of the force from the de/acceleration is transfered to the links.... now that means that high AD will indeed increase this effect .....

Now next point the difference between floating and fixed suspension (this is something I picked up from MTB design lol) now your 3 or 4 link has a floating mount I'll get into this in a min right the fixed (one link, two link, any thing that is fixed to the axle to rotate with the axle) the links become a lever to in effect pull the front down

Now a floating mount (3 or 4 link, where there is a parallelogram effect )... since this style vectors the force up through the links any gain from this would also be vectored...... which would make it less effective

so what ya reckon am I right ?

If so this could explain why some have already proven radius arms on the front keep the nose down when climbing lol

Looks like I'm going to have to make a 1 link or 2 link work for my truck ....

this only applies to us who are 4wd front and rear beam axle LOL, I know what you mean uniformed... it took me ages to work out that the majority of suspension books are for independent axle suspension... and all those taken for granted forces dont work the same for us lol mind you at some stage Im going to have to go back and read em again so I can sort out independent suspension for a hyabusa powered offroad racing buggy I've got in the plans

Edited by De Ranged
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Yea thats the obvious one equal and opposite... wheel goes forward housing has to rotate back to resist .... just on a tangent this is an interesting one to try and take advantage of this, you want your chassis anchor points to be as close to the front of the vehicle as possible

No what I was thinking of was

First does AD really accentuate this effect so far we have one person who has anecdotal evidence.... but by my understanding of the forces is that AS or its reverse AD transfer force from the springs to the links, the greater the % the greater the amount of the force from the de/acceleration is transfered to the links.... now that means that high AD will indeed increase this effect .....

Now next point the difference between floating and fixed suspension (this is something I picked up from MTB design lol) now your 3 or 4 link has a floating mount I'll get into this in a min right the fixed (one link, two link, any thing that is fixed to the axle to rotate with the axle) the links become a lever to in effect pull the front down

Now a floating mount (3 or 4 link, where there is a parallelogram effect )... since this style vectors the force up through the links any gain from this would also be vectored...... which would make it less effective

so what ya reckon am I right ?

If so this could explain why some have already proven radius arms on the front keep the nose down when climbing lol

I've spent too much time under the hot sun today, and now I am struggling with comprehension Lol.

A 3 link with parallel arms when viewed from the side will not have any antidive/squat effect. If you arrange the links so that there is a vertical separation of say 10" at the axle and 5" at the chassis then you will have antidive/antisquat geometry. The link lengths and angle relative to the road surface will determine the % AD/AS. Laterally offsetting the upper link can either magnify or reduce lateral driveline torque roll. If the upper link is mounted left of centre, it should angle down from the axle to the chassis. If mounted to the right of centre, it should angle up from axle to chassis. As you suggested previously, build adjustability into the design if possible so that you can fine tune link angles, vertical separation at chassis etc.

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Yep you are dead right that is how you work out / adjust AS/AD I'm not talking about that

Right lets just talk AS to simplify when you get acceleration you get a weight transfer in resistance to this (inertia) now as the inertia effects the back suspension it causes it to sag the harder the acceleration the more weight the more squat.... AS will resist this (sorry if this is over simplified Im not trying to be insulting its just easier to show this way) now the way it resists this is by transfering a percentage of this force into the links, I know on pirate eveyone assumes AS is an upward force... not quite right

At 100% all the inertia is balanced in the links so your back end doesnt sag, there is no extra weight to push the springs down.... if you doubt me test it

find a pot holed dirt track some where that you are going to leave wheel tracks, coast over it at say 30km/hr now if you walk it you will see your tyre pattern it should have rolled in and out of the pot holes..... now try the same thing accelerating as hard as you can odds on your tracks will not have dropped in to the potholes as much now this is assuming an average car with say 50% AS if you can do this with some thing setup with more AS anything that is setup to do drags you may find that the accelerating tread pattern may not even drop into the far side of the pot holes

This is due to your AS loading up the links this extra mass unbalances your sprung to unsprung ratio, your shock valving is now wrong and the extra mass makes it harder for your spring to move the axle down into the potholes

Now all that makes sense yes ? if it does then apply that to my first paragraph

Now to the second bit about fixed or floating Im a bit peived photobucket wont upload pdf files now I drew up a rough diagram to show this, looks like I'll have to describe it lol

My point wasnt if a link system will pull the front down, it was what link system was best at doing this

Now a fixed link like a radius arm or 1 link that is attached to the axle if the axle wants to rotate then it has to rotate the links... so the counter force of the wheels rotating forward on the front axle wants to make the axle housing rotate back wards rotating the link down simple yep

Now when you have a floating (if you were to disconnect the links from the chassis they would fall down they don't lock to the axle) system the rotation of the diff is countered by the separation of the links at the axle by the top link forcing towards the chassis and the bottom link pulling on the chassis... where is the down force lol.... there is still a force because the links angle towards each other they have an instant center now the closer this is to the axle the more force is going to be turned into downward force.... but it will never compair to a fixed link system for this effect

I hope Ive described it in a way you get what Im thinking

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Just for the books I got a D pass in bursary physics.... oh how I wish Id applied my self in physics and maths lol

If it helps most of my friends now make a point of asking what to do, and state they dont want to know why..... yea Im not the best at explaining things lol

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I thought the StrangeRover name belonged to Alvin Smith from the UK from 30 or so years back who plopped a triumph TR7 body on a RRC chassis?

Anyway, MogRover as I knew and remembered it, continued the rear trailing arms on the same plane as standard, only they were longer. Wouldn't that give the same instant centre as standard, but reduced rear axle roll steer?

Bill, I think there were a few positives. One being less axle roll steer, and from the same thing the axle not coming forward under the vehicle as much on down travel. The other being that if the upper A frame was not altered the new difference in length between the A frame and the longer trailing arms would mean a reduction in the rate that the anti squat raised during down travel.

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De Ranged, I can't hold off any longer from not saying this, your incorrect use of terminology and physics annoys me, to the point that i have to turn away from reading your posts. Sorry but I guess that is because I'm a pedantic old so and so, but it is engrained from years of having to watch out for and correct mistakes before harm results.

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I thought the StrangeRover name belonged to Alvin Smith from the UK from 30 or so years back who plopped a triumph TR7 body on a RRC chassis?

Anyway, MogRover as I knew and remembered it, continued the rear trailing arms on the same plane as standard, only they were longer. Wouldn't that give the same instant centre as standard, but reduced rear axle roll steer?

I'm not surprised there were/are more than one using the name StrangeRover.

I was referring to Sam O. and my thoughts were more about recalling his posts on Pirate, rather than his old hybrid,2A on a rangie chassis, that most likely influenced his user name. It was a very capable vehicle and even more so when the mog axles replaced the Dana 44's (when it became known as MogRover).

MogRover was built on a shoestring and the build with the mog axles was executed in an extremely short time IIRC, before it was taken down to tufftruck, which it very nearly won, competing against more expensive vehicles designed to exploit certain rounds of the competition such as the travel ramp, and show and shine.

I can't recall too much of the suspension geometry, on mogrover and considering how it was developed and changed, don't doubt it may not have been a shining example of an ideal set-up. It wasn't my intention to use mogrover as an example.

Sam built many rock crawling buggies after that, and they would probably be better examples of suspension design. Sam knew his stuff and a lot of people in Australia and on Pirate learned much about good off road suspension practice from him.

Too bad he has gone off in another direction.

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