Follow-up thoughts: Air bag suspension w/leaf spring locators

[1x1_Speed_Craig]

I have seen several mentions of using only the main leaf spring from the leaf pack to just locate the axle, and use air bags for the actual suspension. When I was working on pulling the axle out from underneath my M101A3 last weekend, I got thinking about what I feel is a "project killer" with this idea - spring wrap. I'd love your collective thoughts/input.

The trailer is set up with an SOA suspension. Even if you used long spring perches, and take into account that it's not a drive axle like on a vehicle, I think there would be a lot of "wrapping" force when hitting bumps, and that a single leaf spring would not have the rigidity to resist spring wrap (and unpredictable handling) without the use of a ladder bar of some sort. This may also lead to reactionary fore/aft "wobbling". Visions of "S-bend" YJ or XJ leaf springs also enter my mind. Again, I know it isn't a drive axle, but...

Thoughts?

Craig

 

[JeepN95YJ]

The only way to get springwrap is to incorporate some kind of torque into the axle. In an SOA YJ the torque is introduced by the engine. You get off the throttle and the spring straightens out.

I don't thing wrap is anything you need to worry about on a trailer.

 

[1x1_Speed_Craig]

The only way to get springwrap is to incorporate some kind of torque into the axle. In an SOA YJ the torque is introduced by the engine. You get off the throttle and the spring straightens out.

I don't thing wrap is anything you need to worry about on a trailer.

Are you certain? I'm not talking about "forward & up" wrap from torque, but rather the axle rotating backward upon encountering a pothole, bump, etc. The leverage is going to send the axle/wheel/tire backward & up, it seems.

Also, we're talking about a single leaf spring (not very thick/rigid). In a complete spring pack, the multiple leaves help reduce this. Think of an old-school ('50s-'60s Willy's rear leaf pack vs. a YJ 4-leaf pack...I think they're 4-leaves...it's been a while).

Craig

 

[JeepN95YJ]

I'm trying to envision what could provide the leverage?

The tire/wheel will move slightly because of the spring/shackle combo, but whether it moved up and back, up and down, or up and forward are more a factor of the spring arch.

The tire will not be able to provide any real leverage to wrap the spring because it is attached by a rotational bearing (the wheel bearing) If you twist the tire to try to wrap the spring the tire will just roll.

If your airbag is directly on top of the axle it will not be able to induce the torque either. The only thing that might is the shock if it is mounted off to the side. I still think the force applied to the springs by the shock would be insignificant to induce springwrap.

Am I making sense? Or am I still not getting it?:sombrero:

 

[ntsqd]

If pulling the tire over a rock as tall or taller than the spindle centerline it will want to roll, but it will also want to twist the spring. If you picture the axle at some distance below the spring, say with a lift block, then the leverage to twist the spring becomes more obvious. To me anyway....

 

[12husky]

Brakes

There could be spring wrap under heavy braking if you are using trailer brakes. I am not sure how much, if any, this would bend the spring, but it may.

I think the OP is thinking that say the tire drops in a hole, you now have a rearward force on the lower part of the tire applying torque to the leave spring above the axle. Again, this is possible, but I have no idea how much it would bend the spring.

It may be such that you can remove some, but not all of the springs to balance out between the two. This would narrow up your spring rate adjustment range (airbags + leaf) by raising your lower limit. Not sure if that is making sense.

Anyway, just a thought.

~Matt

 

[JeepN95YJ]

If pulling the tire over a rock as tall or taller than the spindle centerline it will want to roll, but it will also want to twist the spring. If you picture the axle at some distance below the spring, say with a lift block, then the leverage to twist the spring becomes more obvious. To me anyway....

What kind of problem would that cause? The centerline would be within inches of the spring. The leverage would be minimal. How would that affect the suspension negatively?

 

[JeepN95YJ]

There could be spring wrap under heavy braking if you are using trailer brakes. I am not sure how much, if any, this would bend the spring, but it may.

~Matt

BRAKES!:sombrero:

That makes sense. I can see that causing the leverage. Never occurred to me in my earlier posts. I can see heavy braking on a loaded trailer causing spring-wrap and tire chatter. I don't think that would be a fun ride.

 

[1x1_Speed_Craig]

If pulling the tire over a rock as tall or taller than the spindle centerline it will want to roll, but it will also want to twist the spring. If you picture the axle at some distance below the spring, say with a lift block, then the leverage to twist the spring becomes more obvious. To me anyway....

There could be spring wrap under heavy braking if you are using trailer brakes. I am not sure how much, if any, this would bend the spring, but it may.

I think the OP is thinking that say the tire drops in a hole, you now have a rearward force on the lower part of the tire applying torque to the leave spring above the axle. Again, this is possible, but I have no idea how much it would bend the spring.

It may be such that you can remove some, but not all of the springs to balance out between the two. This would narrow up your spring rate adjustment range (airbags + leaf) by raising your lower limit. Not sure if that is making sense.

Anyway, just a thought.

~Matt

Both of these posts convey pretty much what I was trying to get across (sorry for my lack of verbal articulation :elkgrin. I do plan on using trailer brakes in the near future, so the braking comment is much appreciated...something I hadn't though of yet.

As a somewhat similar (but completely different) comparison, I think of the fore & aft movement of my rigid mountain bike fork as I hit bumps. You can actually see the fork moving backward, and it doesn't take huge hits to see it.

Thanks for the feedback!

Craig

 

[ntsqd]

What kind of problem would that cause? The centerline would be within inches of the spring. The leverage would be minimal. How would that affect the suspension negatively?

True, but picture how it would work with a 6" block stuck in there. The effect is the same, only the magnitude of the displacement changes with the available leverage.

What about using the front spring eye mounts for a simple ladder bar design similar to what I posted in your other thread?

 

[1x1_Speed_Craig]

What about using the front spring eye mounts for a simple ladder bar design similar to what I posted in your other thread?

That's most likely the route I'll go, only I'd probably position the frame mounts further forward on the frame to allow for longer arms. I mainly wanted to ask the questions, get peoples' input, and confirm my suspicions for anyone else who might be searching for information on the same topic.

Craig

 

[R_Lefebvre]

I think I missed most of this discussion, but if I have it right, NTSQD's idea is probably the correct one. Forget about a leaf spring. Just use a trailing arm on each side of the axle. The airbag goes behind the axle. This gives more room for a taller bag with more compliance.

If I were to do it all again, this is what I'd do. This is how many heavy equipment trailers are built.

 

[Hill Bill E.]

Just use a trailing arm on each side of the axle. The airbag goes behind the axle.

Wouldn't this require a trac-bar, or angled/triangulated arms to locate the axle? (keep it from shifting side to side)

I agree with using trailing arms, instead of a mainspring, easier to do, and less to go wrong on the trail.

 

[1x1_Speed_Craig]

I think I missed most of this discussion..

Wouldn't this require a trac-bar, or angled/triangulated arms to locate the axle? (keep it from shifting side to side)

Yes, it would.


Again, the topic of this thread was regarding using leaf springs to locate the axle...

 

[ntsqd]

Rob, my suggestion for linkage would be the second picture in this post: http://www.expeditionportal.com/forum/showpost.php?p=626702&postcount=25

As far as using leaf springs to do the location and air springs to do the suspending, I'm sure that it has been done. I don't think that it is an ideal method, but it probably works.