3 link vs radius arms

[MaXJohnson]

MaXJohnson, thanks, I've gotten into the habit of always referring to it as anti-dive when dealing with a front axle. It's odd terminology anyways, why do people even talk about 80% anti-squat rather than an amount (120%?) of squat... or why not call it lift rather than anti-squat... why not dive rather than anti-lift... why not lift rather than anti-dive... etc, etc

the pitching moment that results in squat, dive & lift is always there(100%), based on the location of the sprung mass CG. Your suspension links counter-act ("anti")the pitching moment to a varying degree(% "anti") based on the side-view design of the links. 100% of the pitching moment is transmitted to the springs unless your suspension links are designed such that a percentage of the pitching moment is carried through the suspension links. At 100% anti-pitch(squat/dive/lift), the links are reacting to all of the available pitching moment, resulting in no change in compression or extension of the spring. Anti-squat/dive/lift does not change the amount of weight transfer at the axle, just the way it is applied. Too much anti-pitch increases the effective spring rate which is counter productive in maintaining tire contact with the ground.

 

[Goatman]

I would much rather have radius arms on both sides than on one side and the other with a single lower. The small loss in flex would be worth having even suspension characteristics. When you run only one upper (or wristed arms for Ford radius arms) all the anti-dive properties are transferred to only one side of the vehicle, meaning the suspension and traction will behave very differently with one side stuffed vs. the other side stuffed.

Better is a parallel 3 link (w/ panhard). Make the uppers roughly 75% of the lowers length, and the seperation at the frame roughly 75% of the seperation at the axle and it will function pretty well. If you want to get more complicated you can use the 4 link calculator (found on the Pirate board in Triaged's sig) and figure out the exact anti-dive.

This advice is based on..........?

I love it when a front leaf spring guy gives advice about link suspesnsions. I think he should have to post on link threads with a disclaimer "take this advice with a grain of salt, I run leaves all around".

Yeah, Brett, I've been gone for awhile.......but I'm baaaack. :wave:








I do have to say, though, in Brett's defense, that he has studied link suspensions and has most of the concepts down.......though no direct experince. I get a kick out of him posting on both the link and leaf spring threads.

 

[Goatman]

anti-dive is the main thing.

anti-dive is massively influential in affecting how effectively your vehicle puts power to the ground (traction)

This sounds really good, but it's not true. Anti-dive will effect how a lifted rig with big tires handles on the road, and can (should to a degree) be a concern, but has little to do with trail performance. The forces are minimal at slow trail speeds, and traction, rather than braking behavior, is the real issue.

Few of us have problems with traction in the front on boulder fields or ledges, it's the steep climbs that make a difference.* Here weight transfer has a large effect, as well as how well the rear axle stays planted. Anti-squat in the rear will have a MUCH bigger effect on climbing performance than how much anti-dive is in the front. Since weight transfer is the big issue, a limiting strap helps out, and will mask any small effect of too much anti-dive/lift/pitch in the front. Basically, running an adjustable limiting strap on the front negates the point of most of these arguments that have to do with traction. Street/road handling is still an issue, though, especially on rigs with tall lifts.

Unloading also has a big effect on traction on steep climbs, and there are many factors that contribute to unloading. Too much anti-dive/pitch can have an effect, but there isn't always enough traction in the front to get those forces involved. Spring height and spring force at full droop will effect unloading, where the spring can push up too much at close to full suspension extension in the front. In my opinion, too long of an arm can contribute to unloading. The weight of the front axle will pull down on the chassis to some degree, especially when the suspension is at or close to full extension, and the longer the arms are the further back on the chassis this weight is applied, further effecting weight transfer on steep climbs. Of course, again, a limiting strap will change the point at which this weight is applied, moving it much further forward, and virtually negating the argument.

* Front link suspensions inherently climb (in the front) better than leaf springs because the links tend to push the tire into the obstacle, creating more traction.

 

[Beej]

More please, I need more...
This is much better than sitting through class...

 

[BrettM]

This advice is based on..........?

I love it when a front leaf spring guy gives advice about link suspesnsions. I think he should have to post on link threads with a disclaimer "take this advice with a grain of salt, I run leaves all around".

Yeah, Brett, I've been gone for awhile.......but I'm baaaack. :wave:








I do have to say, though, in Brett's defense, that he has studied link suspensions and has most of the concepts down.......though no direct experince. I get a kick out of him posting on both the link and leaf spring threads.

1 Point for the Goatman

however, in my defense... I've done a lot of study and research (though mostly for rear link-suspensions, since I'm happy with my leafs up front and will very soon be linking the rear).

I've seen, ridden in, and drove a good handful of 4x4s with radius arm fronts, single radius arm fronts (one upper), and 3 links. I would personally rate the 3 links a 9 (nothing's perfect), the dual-radius arms a 6 or 7, and the single radius arm a 3. (if you're curious, I would rank front leafs a 5) I can't stand the uneven characteristics of a single radius arm.

 

[BrettM]

More please, I need more...
This is much better than sitting through class...

more what? if you have any specific questions someone might be able to answer them.

 

[cyrus]

Thanks guys, this has been a very educational thread, even if most disussion was based off personal preference, with some very in depth explinations. I believe I will stay with the radius arms. Simplicity in this case wins. my rig will most likly not see more than a few miles of road time, from trail to trail. Goatman, thanks for the input.

Have a good one guys,
Thanks again for the help.

 

[Beej]

more what? if you have any specific questions someone might be able to answer them.

Could you elaborate on your rating system above, and explain a bit more detail about how you came up with those comparisons and why? I just want to learn more...

 

[XJoachim]

This sounds really good, but it's not true. Anti-dive will effect how a lifted rig with big tires handles on the road, and can (should to a degree) be a concern, but has little to do with trail performance. The forces are minimal at slow trail speeds, and traction, rather than braking behavior, is the real issue.

Few of us have problems with traction in the front on boulder fields or ledges, it's the steep climbs that make a difference.* Here weight transfer has a large effect, as well as how well the rear axle stays planted. Anti-squat in the rear will have a MUCH bigger effect on climbing performance than how much anti-dive is in the front. Since weight transfer is the big issue, a limiting strap helps out, and will mask any small effect of too much anti-dive/lift/pitch in the front. Basically, running an adjustable limiting strap on the front negates the point of most of these arguments that have to do with traction. Street/road handling is still an issue, though, especially on rigs with tall lifts.

Unloading also has a big effect on traction on steep climbs, and there are many factors that contribute to unloading. Too much anti-dive/pitch can have an effect, but there isn't always enough traction in the front to get those forces involved. Spring height and spring force at full droop will effect unloading, where the spring can push up too much at close to full suspension extension in the front. In my opinion, too long of an arm can contribute to unloading. The weight of the front axle will pull down on the chassis to some degree, especially when the suspension is at or close to full extension, and the longer the arms are the further back on the chassis this weight is applied, further effecting weight transfer on steep climbs. Of course, again, a limiting strap will change the point at which this weight is applied, moving it much further forward, and virtually negating the argument.

* Front link suspensions inherently climb (in the front) better than leaf springs because the links tend to push the tire into the obstacle, creating more traction.

Thanks, you second my findings. :wave:

 

[BrettM]

Could you elaborate on your rating system above, and explain a bit more detail about how you came up with those comparisons and why? I just want to learn more...

well obviously those are not scientific results, but just the way I feel about those systems. There are obvious simplicity (and cost) factors where leafs or radius arms beat out a 3 link.

3 links are great (when built right, any good idea can be screwed up), they flex great, they follow the travel of the steering, they can be built to counteract engine torque on the body, they don't unload on climbs, etc.

Radius arms are also pretty good, they flex good enough, follow the travel of the steering, control axle wrap fairly well, are pretty easy to build, BUT they need a limit strap(s) to control unloading, and they need bushings in all then ends so there is a little more play than ideal.

Leafs are cheap and very simple to build, flex good enough, are very stable due to roll-center and interleaf friction, don't unload on climbs, BUT do not follow the arc of the steering, and can experience axle wrap.

A single radius arm is simple to build, flexes great, follows the travel of the steering, BUT they need a limit strap to control unloading, and the big thing is they make for some scary situations off-camber and otherwise when the single radius arm is trying to flip the rig over to one side. I don't at all think the small gain in flex between one radius arm and two is at all worth the often scary handling of all the axle's rotational forces being sent to one side of the Jeep.

 

[XJoachim]

First, we did never talk about cost or simplicity, sure nothing beats a leaf setup in those categories, but that's it.

Second, you may have been sitting in a similar rig but i doubt the suspension was something near than well engineered.

Third, leafs DO unload on climbs but since they do not flex much they don't unload as much as any other working suspension.

Fourth, a bushing does not provide play, if it does it is defective.

I'm working on my suspension for about 18 months now and i still see some negatives to work out. But nothing extreme, that's just fine tuning. I want to stretch the wheelbase another 5" and redesign the rear crossmember but that's all i plan to do. So bad i'm not able to show you what i've done and how it works, maybe i could be able to change your mind.

I don't know why you're saying that the single radius arm is "trying to flip the rig over to one side". What side should that be relative to the radius arm, the same or the opposite? I'm running this setup for more than a year now and i never realized or recognized that.

 

[bj-666]

when you apply rotational forces to the tires (throtle/brake) it trys to twist the axle with a single radius arm that force is trancfered to only one side. but on the other hand i see the same thing happening in a 3 link (i'm no expert)

 

[BrettM]

this is true, but with a single radius arm you are applying a ton of anti-squat to one side, but with a well designed 3 link you are sending a fairly neutral anti-squat to the one side. You can even engineer it (there's a specific equation for distance from center of the upper depending on gear ratio and link angles) so that it counteracts engine torque which pulls the vehicle to the passenger side.

 

[XJ_ranger]

More please, I need more...
This is much better than sitting through class...

dont you teach the class?

 

[Beej]

dont you teach the class?

True, but good lord, am I boring!

 

[Dirk Pitt]

True, but good lord, am I boring!

No shit!

:speepin:

:laugh3:

 

[jeep_87_cherokee]

in the front with a dana 30. is a 3 link with panhard bar able to be used with the lower control arms trianglulated , and does it help for the to be that way or is it just better to keep them parrallel , and would there be a benefit of trianglulateing the lower control arms