long arms and unloading issues

[jeeperjohn]

So the unloading is because you have so much suspension travel?

Unloading is caused by suspension geometry. It could happen even with not much travel. It just depends on how the links are arranged. I have not heard of many complaints where people had a big problem with unloading. It also depends a great deal on what kind of wheeling you do. Limit straps are a fairly cheap and effective way to deal with unloading.

 

[Rock Yacht]

I get asked this question quite a bit and I remind people that there is another aspect to this that gets ignored and that's the effect of the rear suspension on the front. Under torque the rear pinion wants to raise up. In turn, that same torque at the leaf spring pad causes the axle to want to rotate (lift) the spring up in the front and downward (pull down) in the rear. On a steep enough incline this force can act as a lever causing the front end to want to lift.

Rarely ever will you hear a TJ/LJ/ZJ owner talk about unloading even with a radius arm setup in the front.

The geometry of the radius arms can play a role in it as well. We have tried very hard to get our radius arm geometry as good as we can in order to reduce the possibility of unloading.

I'm not an engineer but this is how it has been explained to me so don't flame me, I'm just a sales guy

Rod

 

[redrider2911]

I get asked this question quite a bit and I remind people that there is another aspect to this that gets ignored and that's the effect of the rear suspension on the front. Under torque the rear pinion wants to raise up. In turn, that same torque at the leaf spring pad causes the axle to want to rotate (lift) the spring up in the front and downward (pull down) in the rear. On a steep enough incline this force can act as a lever causing the front end to want to lift.

Rod

I am glad somebody else bought this up. I have been mulling over thoughts on this subject for quite some time. I am not a proffessor in physics by any means but let me try to explain how i see it.
First off, unloading is a term that is widely used and often in the wrong context in relation to linked suspension and geometry. Like Rod said, the back plays into the front "unloading" period, on a steep climb or on flat ground... So lets break that term "unloading" down. When your front suspension unloads it is the springs decompressing because the whole weight of the front of the vehicle is no longer resting on the springs. This happens under acceleration and steep climbs from the back axle tranfering torque into the chasis and so on like earlier explained, and of course gravity. Now lets say you were able to do a wheely, the torque transfered to the ground from the rear end would cause the front end to come up and the springs would unload, now explain to me how the front link geometry has anything to do with that, even if you were in 4 wheel drive.
So after trying to make sense out of all that, now lets talk about forces exherted from the front end. Just like the back, when torque travels through the front axle and wants to turn the tires and transfers a counter torque through the front links and into the chasis this would be anti-dive. Depending on how much anti-dive you have from your link geometry the front AXLE will either be PUSHED DOWN or PULLED UP to the body from the torque. (notice the choice of words.) Just over 100% anti-dive would mean the front axle PUSHES the body up away from the ground which means the axle itself is being pushed TOWARDS the ground. MEANING MORE TRACTION. Yes the springs will decompress a little which seems like they are "unloading" but I dont see it that way. And yes, too high of numbers over 100% anti-dive can cause problems like the springs completely "unloading" and falling out.
That said, the main reason I wanted to write this is because everyone kept on saying that certain setups cause the front end to just "unload" without any explanation when there is alot more to it than that. The whole front end isnt unloading, the geometry of the links are putting forces on the front end causing the body and axle to push apart from each other and leave the spring in the middle without as much pressure on it.

Im sorry if my thought process was really confusing but alot goes on in my head at once. lol
Like I said, just my thoughts on the whole thing and how it makes sense to me in my head.:lecture:
Now tell me im crazy.. :looney:

 

[winkosmosis]

I get asked this question quite a bit and I remind people that there is another aspect to this that gets ignored and that's the effect of the rear suspension on the front. Under torque the rear pinion wants to raise up. In turn, that same torque at the leaf spring pad causes the axle to want to rotate (lift) the spring up in the front and downward (pull down) in the rear. On a steep enough incline this force can act as a lever causing the front end to want to lift.

Rarely ever will you hear a TJ/LJ/ZJ owner talk about unloading even with a radius arm setup in the front.

The geometry of the radius arms can play a role in it as well. We have tried very hard to get our radius arm geometry as good as we can in order to reduce the possibility of unloading.

I'm not an engineer but this is how it has been explained to me so don't flame me, I'm just a sales guy

Rod

The force you're talking about is the same as the force that causes a motorcycle or drag racer to wheelie. The suspension in between the rear wheels and the Jeep doesn't really matter, it would happen no matter what was back there.

I also don't see how the front suspension geometry would matter. It's a simple upward force on the front end. You might as well hook a crane to the bumper and pull upward. How would suspension geometry change anything?

 

[winkosmosis]

I am glad somebody else bought this up. I have been mulling over thoughts on this subject for quite some time. I am not a proffessor in physics by any means but let me try to explain how i see it.
First off, unloading is a term that is widely used and often in the wrong context in relation to linked suspension and geometry. Like Rod said, the back plays into the front "unloading" period, on a steep climb or on flat ground... So lets break that term "unloading" down. When your front suspension unloads it is the springs decompressing because the whole weight of the front of the vehicle is no longer resting on the springs. This happens under acceleration and steep climbs from the back axle tranfering torque into the chasis and so on like earlier explained, and of course gravity. Now lets say you were able to do a wheely, the torque transfered to the ground from the rear end would cause the front end to come up and the springs would unload, now explain to me how the front link geometry has anything to do with that, even if you were in 4 wheel drive.
So after trying to make sense out of all that, now lets talk about forces exherted from the front end. Just like the back, when torque travels through the front axle and wants to turn the tires and transfers a counter torque through the front links and into the chasis this would be anti-dive. Depending on how much anti-dive you have from your link geometry the front AXLE will either be PUSHED DOWN or PULLED UP to the body from the torque. (notice the choice of words.) Just over 100% anti-dive would mean the front axle PUSHES the body up away from the ground which means the axle itself is being pushed TOWARDS the ground. MEANING MORE TRACTION. Yes the springs will decompress a little which seems like they are "unloading" but I dont see it that way. And yes, too high of numbers over 100% anti-dive can cause problems like the springs completely "unloading" and falling out.
That said, the main reason I wanted to write this is because everyone kept on saying that certain setups cause the front end to just "unload" without any explanation when there is alot more to it than that. The whole front end isnt unloading, the geometry of the links are putting forces on the front end causing the body and axle to push apart from each other and leave the spring in the middle without as much pressure on it.

Im sorry if my thought process was really confusing but alot goes on in my head at once. lol
Like I said, just my thoughts on the whole thing and how it makes sense to me in my head.:lecture:
Now tell me im crazy.. :looney:

I think what people mean by "unloading" is the front suspension extending. That affects the linkages and all that, but I also don't see how it would affect the force of the tires on the ground.

For a simpler example, think of a dirt bike's rear cantilever suspension. As you apply throttle, the cantilever extends because of the angle BUT the force of the tire on the ground isn't affected. It's the same as if the bike had no rear suspension at all. Otherwise you could build a vehicle that either reduces or increases the load on all tires just by applying throttle.

 

[sunburned]

Everyone that thinks front suspension doesn't have anything to do with the front end coming off the ground has never drag raced. People mod their front suspension just as much as the rear to get proper weight transfer to the rear tires, meaning the front comes off the ground. Usually this is done more with spring rates and different shocks, but I'm sure suspension geometry could possibly come into play. Not saying the radius arms are bad, but don't think that leaf springs are the only thing causing the front end to come up.

 

[89xj]

its becuase the y-link doesnt have an upper arm(3-link) or arms(4-link) that connects the frame to the axle, thats why a y-link could "unload", while a 3 or 4 link doesnt.

the upper arm(s) holds the front end down via connection from frame to axle.

 

[Jeep450r]

All link style setups will unload under different circumstances... Radius arms are not the only ones that unload.

 

[GordoSmasho]

With a short arm lift the "unloading" is not as noticeable because there is less overall front axle travel in the suspension. I know that is a crude way of explaining it but thats what i got.

In a steep climb it allows for more weight transfer to the rear making the front lighter on the suspension. When this happens there is less weight transferred to the ground by the front tires creating a low traction situation for the front tires. right?

When you have a suspension system that allows more overall axle travel that situation is exaggerated. So having a center limiting strap will help curb this from happening while still allowing articulation. right?



Just making sure i understand. I will be installing long arms soon.

 

[Deadman 94 xj]

Nevermind my paint skills

The reason a radius arm setup will unload theoretically more than a true 3/4 link is because there is no upper arm that connects to the "frame". That upper arm acts as a "helper" to keep the front of the jeep close to the axle because of the increased axis (shown in red).

A radius arm does not have that upper arm so the axis is reduced:

That said, there is more to it than that. The length of the arms in a radius AND in a true 3/4 link setup also plays a role. Typically any "long" arm system will unload because the longer arm increases the distance between the the connection at the frame (axis) and the axle. So a true 3/4 link will unload also because the axis has been decreased, because of the arm length. Most after market bolt on kits don't come with enough separation at the axis to really take advantage of the upper arm anyway. So the differences between those and a radius setup, although present, are really exaggerated.

If that's true than a mid / short arm setup is the only real way to decrease unloading.

Strictly looking at radius / y link setups, there is also the geometry at the connection point (axis) to consider. You take a high clearence setup where the arms connect up higher into the chasis, you're going to get more unloading because there's less force being used by the arms to hold the axle close the the frame. Generally the steeper the angle, the less unloading.

As far as the rear suspension goes, axle torque has a lot to do with it but so does rear suspension stiffness. If the rear is soft and able to "give in" than it's going to compensate for the front. If it's stiff than the front has nowhere to go. If a traction bar is added than the rear can actually counteract the unloading by forcing the front down, by forcing the rear up.

IMO, the bottom line is don't worry about it until you're ready to take advantage of building your own setup.

 

[winkosmosis]

Deadman I think you're talking about the tendency of torque to want to rotate the whole axle and therefore the suspension arm... right? The wheels are turning forward, the axle wants to turn backwards, and that rotation force makes the radius arm swing and pull the axle upward. That doesn't affect the force on the ground though.

Alos, the longer the arm, the smaller the effect

 

[Deadman 94 xj]

Deadman I think you're talking about the tendency of torque to want to rotate the whole axle and therefore the suspension arm... right? The wheels are turning forward, the axle wants to turn backwards, and that rotation force makes the radius arm swing and pull the axle upward. That doesn't affect the force on the ground though.

Alos, the longer the arm, the smaller the effect

Front axle torque has nothing to do with it. The longer the arm the more unloading.

 

[98xjjeeper]

Front axle torque has nothing to do with it. The longer the arm the more unloading.

No. The front axle torque has everything to do with it. Its the fact that the axle wants to twist and when weight come off the frontend like climbing a hill, the radius arms make it easier for the axle to lift the body more. Therefore unloading. The shorter the arm the easier it is to unload but they will only drop so far. The longer the arm the harder it is to unload but father it can drop. Three and 4 link setups can be setup to where you don't have this problem.

 

[muddeprived]

No. The front axle torque has everything to do with it. Its the fact that the axle wants to twist and when weight come off the frontend like climbing a hill, the radius arms make it easier for the axle to lift the body more. Therefore unloading. The shorter the arm the easier it is to unload but they will only drop so far. The longer the arm the harder it is to unload but father it can drop. Three and 4 link setups can be setup to where you don't have this problem.

For some reason this does not sound right unless i'm reading it wrong.

 

[FloydXJ]

As far as the effect on traction, it is weight transfer as far as I am concerned. The steeper angle the chassis is at, the more weight is going toward the rear end. If the front end is limited, the angle will not get made steeper in the driver seat on account of the unloading. If you are at less of an angle, there is more weight on the front tires. How much? I don't know.
This applies to body/frame/cargo weight only, of course. Drivetrain-wise, there should be no change.

I have a Clayton radius, and this has not been a major issue, although I want to hook up a center limit and see what happens just for steep climbs.

 

[winkosmosis]

No. The front axle torque has everything to do with it. Its the fact that the axle wants to twist and when weight come off the frontend like climbing a hill, the radius arms make it easier for the axle to lift the body more. Therefore unloading. The shorter the arm the easier it is to unload but they will only drop so far. The longer the arm the harder it is to unload but father it can drop. Three and 4 link setups can be setup to where you don't have this problem.

But the torque of the wheels would be forcing the arms and axle upward

 

[winkosmosis]

As far as the effect on traction, it is weight transfer as far as I am concerned. The steeper angle the chassis is at, the more weight is going toward the rear end. If the front end is limited, the angle will not get made steeper in the driver seat on account of the unloading. If you are at less of an angle, there is more weight on the front tires. How much? I don't know.
This applies to body/frame/cargo weight only, of course. Drivetrain-wise, there should be no change.

I have a Clayton radius, and this has not been a major issue, although I want to hook up a center limit and see what happens just for steep climbs.

So just having more downward suspension travel allows the front suspension to push the front end up more. Therefore limiting the downward travel stops the suspension from raising the front end more than that limit?

That makes more sense than any other of these other ideas blaming the length of the longarms.

 

[Deadman 94 xj]

So just having more downward suspension travel allows the front suspension to push the front end up more. Therefore limiting the downward travel stops the suspension from raising the front end more than that limit?

That makes more sense than any other of these other ideas blaming the length of the longarms.

When you learn a little more young jedi, you'll see that I was right.

I'm sure you'll go back and find a reason to be right. That's ok. The internet is full of BS.

Front traction / torque has NOTHING to do with unloading. The length on the arms DOES play a significant role in the amount of unloading that will occur.

I'm surpised guys like Goatman and the others aren't commenting. It's them that I learned this stuff from...

Either way, have a nice day. I can only lead a horse to water.

 

[ROBZ95Xj]

watch the tj in this vid look at the insane unloading, he like so alomost went over backwards, seriously run what ya want, peaple need to shut up and wheel already

http://www.youtube.com/watch?v=ZzLmDlBi4UI

 

[redrider2911]

I still think that the back end has more to do with it than anything. The way I look at it, with a center limiting strap the jeep body would actually have tendency to pull the front axle off the ground, creating less traction and wheel hop.