R_Lefebvre
Expedition Leader
Why would the lateral arms try to twist? We must be thinking of different systems.
Trailer Building Indepent Arm Building - Official Guide
- Thread starter dieselcruiserhead
- Start date
R_Lefebvre
Expedition Leader
So you're thinking double wishbone. That's not what I had in mind. I'm thinking more along the lines of a twin I-beam suspension. Only problem is the camber changes as the load compresses the suspension. Mind you, that's negated by an airbag system to level it.
Or like on the back of a Neon or Subaru (IIRC). Two lateral links and two trailing arms. Each is a simple two-force member. No twisting. Fairly simple to build.
But I think I see what you're saying. In a system purely made with lateral links, like double wishbone/SLA, the arms get pushed back when the wheels hit bumps. On most modern cars, Fords I know particularly, this is actually by design. That's why they go with an "L" shaped arm. There is a stiff bushing at the base of the "l" to control camber loss in corners, but the rear bushing at the end of the "_" is soft. It allows the wheel to recess on bump. Kinematic recession.
But that's all unecessary on a trailer. I'd use a system with a trailing link to control fore-aft motions.
Or like on the back of a Neon or Subaru (IIRC). Two lateral links and two trailing arms. Each is a simple two-force member. No twisting. Fairly simple to build.
But I think I see what you're saying. In a system purely made with lateral links, like double wishbone/SLA, the arms get pushed back when the wheels hit bumps. On most modern cars, Fords I know particularly, this is actually by design. That's why they go with an "L" shaped arm. There is a stiff bushing at the base of the "l" to control camber loss in corners, but the rear bushing at the end of the "_" is soft. It allows the wheel to recess on bump. Kinematic recession.
But that's all unecessary on a trailer. I'd use a system with a trailing link to control fore-aft motions.
R_Lefebvre
Expedition Leader
Yeah, that's EXACTLY what I was thinking of. I believe those have longitudinal links to control fore/aft.
Camber is set by simply having the spindle cast onto the lateral arm. That's why that truck in the air has huge positive camber, because the arms are drooping.
I don't think it would be great on a trailer unless you had a way to level it, such as airbags.
R_Lefebvre
Expedition Leader
Yeah, simple trailing arm makes a lot of sense in this application, the only issue is not being able to get the spring inline with the loadpath. Now, if you went with a semi-trailing arm you could, but then you get toe movement on bounce. :\
GeoTracker90
Adventurer
dieselcruiserhead
16 Years on ExPo. Whoa!!
Yes I believe those are the ones.. Thanks Mike..
This is all a very good discussion. After really considering all of the points made here, it still seems like a trailing swingarm setup perfected by A/T is really the most simple and practical arangement. All of the side issues such as mounting loads, offset springs, etc, can be fixed with proper sizing and fabrication of the structural components. All other points seem a bit moot. If you start playing around with a beam axle, you're increasing your unsprung weight, adding a significant "catch-all" between the two wheels, and creating a linkage which is quite complicated (and may not flex well). Leaf springs are old technology and aren't worth discussion. Any discussions of double wishbone arangements is just frightening...way too many moving/wearable parts...and do you really want to have to consider an alignment on your trailer? TTB is an interesting idea, but TTB only has correct camber at one suspension position. This could obviously be aided with airbags, but you still have significant structural considerations with a system like this, and it still would be multi-link unless you wanted to have incredably beefy TTB arms and frame mounts (huge moment-arm).
I'd say the only real contender is the trailing arm suspension which was demonstrated at the birth of this thread. There are ome obvious improvements to be made to that particular example, but the application is sound and is as simple as possible given the performance it provides.
Fabulous thread folks.
Spence
I'd say the only real contender is the trailing arm suspension which was demonstrated at the birth of this thread. There are ome obvious improvements to be made to that particular example, but the application is sound and is as simple as possible given the performance it provides.
Fabulous thread folks.
Spence
G-force
Adventurer
New to this thread, but i like it:ylsmoke:
A question that rises in my head, is lenght on the trailing arms? Is longer better? Up to a point where its not possible to have them longer, of course.
I am about to start a trailer build, hopefully with independant suspension, airbags, and Rancho 9000 shocks. With this, another of my conserns is the different loads on the different points of the suspension.
Lets say about 75 kg on the hitch. Is the rest of the load on the air bag, and then on the axle? Of course then the airbag is mounted center on top of the axle. Not further forward, as proven no good.
Is there any downward force on the bushings, up front on the trailing arms? Or is the load divided between the axle and the hitch?
Thanks again guys. This is good info.
A question that rises in my head, is lenght on the trailing arms? Is longer better? Up to a point where its not possible to have them longer, of course.
I am about to start a trailer build, hopefully with independant suspension, airbags, and Rancho 9000 shocks. With this, another of my conserns is the different loads on the different points of the suspension.
Lets say about 75 kg on the hitch. Is the rest of the load on the air bag, and then on the axle? Of course then the airbag is mounted center on top of the axle. Not further forward, as proven no good.
Is there any downward force on the bushings, up front on the trailing arms? Or is the load divided between the axle and the hitch?
Thanks again guys. This is good info.
ntsqd
Heretic Car Camper
G-Force, your loading questions are best answered by breaking down the components into simple "Free Body Diagrams" (FBD). Diagram the frame and the trailing arm individually. From the frame FBD you'll have the numbers to put into the trailing arm FBD.
http://www.expeditionportal.com/forum/showthread.php?t=32330
As to the ideal trailing arm length, I'm not sure that there is one. With a really long arm that is at a shallow angle at static ride height there is the argument that could be made for it's low rearward motion in compression travel not being advantageous. OTOH a really short trailing arm, which would exhibit a lot of this rearward motion, might make fitting fenders tightly to the tires a bit of a problem. I'd say judgment call, go with what feels right to you.
http://www.expeditionportal.com/forum/showthread.php?t=32330
As to the ideal trailing arm length, I'm not sure that there is one. With a really long arm that is at a shallow angle at static ride height there is the argument that could be made for it's low rearward motion in compression travel not being advantageous. OTOH a really short trailing arm, which would exhibit a lot of this rearward motion, might make fitting fenders tightly to the tires a bit of a problem. I'd say judgment call, go with what feels right to you.