Home built independent suspension?

ntsqd

Heretic Car Camper
Like most of us, I've messed about with various trailers, but wouldn't call myself an expert on them. The M.M. Smith books are a good ref for building trailers, but AFAIK they only deal with leaf sprung designs.

Just want to make sure we're all on the same bushings page. What I'm picturing for a bushing is the typical leaf spring bushing or Hega bushing type shape, a flanged bushing that pushes into a tube. Can be had in either rubber or urethane. Based on Ace Motorsports' Stock Full results with both types of radius arm bushings and subsequent observation & experience I prefer rubber to urethane, but urethane - at least in the States - is a whole lot easier to get in convenient sizes.

Both have pivot designs have their pluses & minus'. In the continuous design the arm should be more rigid at the pivot (which would have an influence to some degree or other on the rest of the arm), but at the expense of a potentially rediculously long bolt (or custom fab'd 'axle'), only two bushing inserts, and only 2 mounting ears.
The 2 bushing design likely uses a off-the-shelf bolt length, 4 bushing inserts, and 4 mount tabs, but may give up some pivot area rigidity.

Were I building it I'd go with 2 bushing tubes & 4 tabs. Design the arms so that one fixture builds either of them (& the spare!). Use a long, straight bar or some similar method to maintain the tab alignment.

Just had a thought, what is the argument against the rubber torsion suspensions? One of those could be used with a shackle to the arm rather than actually having the wheel & tire mounted to it. Probably the "stuffing it's a__ with bricks" method, but it sure would make people scratch their heads trying to figure it out. Could even easily make the shackle length adjustable to vary ride height.
 

UK4X4

Expedition Leader
bushings...

I've ordered the 3" ones with zerk for mine

mid_4-LinkWeldonBarEndswZerkFitting.jpg



http://www.suicidedoors.com/4-LinkWeldonBarEndswZerkFitting.php
 

GeoTracker90

Adventurer
So has anybody come up with an air bag spec yet? Here are some specs on the two that are offered by Suicide Doors.

Suicide Doors - Air Bags

Firestone 224c 2600

2600 lb. 3/8" single port air bag
Min. Height: 3"
Installed Height: 5"-5.5"
Max Height: 8"
Diameter(Inflated): 8"

Firestone 255c 2500
2500 lb. 3/8" single port air bag
Min. Height: 3"
Installed Height: 4.5"-5"
Max Height: 7"
Diameter(Inflated): 6.5"

I like the 8" max height of the first bag compared to the 7" max height of the second bag, but I also like the 6.5" diameter of the second bag more than the 8" diameter of the first bag. What to do? What to do?

Mike
 
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UK4X4

Expedition Leader
Firestone 6782 are the ones I bought

Style: 267C1.5

2500lbs rated

Compressed Height: 2.80"
Extended Height: 8.30"
Ride height: 5.50" - 6.50"
Max. Diameter: 6.60"


For the travel was important, and i did'nt want the 8" OD ones...
this one gives 5.5 " of travel
 

Grim Reaper

Expedition Leader
GeoTracker90 said:
So has anybody come up with an air bag spec yet? Here are some specs on the two that are offered by Suicide Doors.

Suicide Doors - Air Bags

Firestone 224c 2600

2600 lb. 3/8" single port air bag
Min. Height: 3"
Installed Height: 5"-5.5"
Max Height: 8"
Diameter(Inflated): 8"

Firestone 255c 2500
2500 lb. 3/8" single port air bag
Min. Height: 3"
Installed Height: 4.5"-5"
Max Height: 7"
Diameter(Inflated): 6.5"

I like the 8" max height of the first bag compared to the 7" max height of the second bag, but I also like the 6.5" diameter of the second bag more than the 8" diameter of the first bag. What to do? What to do?

Mike
Well remember that wheel travel is governed by where you put it on the A-Arm. The closer to the pivot the more travel you will have at the wheel. 2 inches farther up the A-Arm the 7 inch bag will have the same wheel travel as the 8 inch. Knowing that I think I might be tempted to go with the smaller diameter of the 2500. Still plenty of weight capacity.
 

GeoTracker90

Adventurer
UK4X4 said:
Firestone 6782 are the ones I bought

Style: 267C1.5

2500lbs rated

Compressed Height: 2.80"
Extended Height: 8.30"
Ride height: 5.50" - 6.50"
Max. Diameter: 6.60"


For the travel was important, and i did'nt want the 8" OD ones...
this one gives 5.5 " of travel

Do you have a link to where a guy can find this airbag? Any idea what you gave for these? The others that I posted about were in the $65.00 - $70.00 range each.
 

ntsqd

Heretic Car Camper
The flip side of the travel ratio that Grim mentioned is that it works against load capacity. Just thought I'd mention that in case it was slipping notice.
 

UK4X4

Expedition Leader
Did you manage to source the DOM axle tubing 1/4" wall and 1.75" ID ?

and if so where ?

Cheers
 

GeoTracker90

Adventurer
UK4X4 said:
Did you manage to source the DOM axle tubing 1/4" wall and 1.75" ID ?

and if so where ?

Cheers

Not yet, but thanks for reminding me. I just sent a request to the following company:

www.complete4x4.com

We'll see what they say when they respond. I asked them to quote two pieces 2-1/2' long each. I could probably use shorter pieces but you know the old saying, "I cut it too short, so I cut it again and it still wasn't right..."

MIke
 

Grim Reaper

Expedition Leader
ntsqd said:
The flip side of the travel ratio that Grim mentioned is that it works against load capacity. Just thought I'd mention that in case it was slipping notice.


True, directly over the axle it would be over 5200lb capacity.

A trailer like this would be really fat at 2500lb. 20 inch long arm if he mounted the bag 4-5 inches off the axle center line he should still be over 4000lb and gain 2-3 inches of wheel travel depending on the angle of the A-Frame.
 

GeoTracker90

Adventurer
Grim Reaper said:
True, directly over the axle it would be over 5200lb capacity.

A trailer like this would be really fat at 2500lb. 20 inch long arm if he mounted the bag 4-5 inches off the axle center line he should still be over 4000lb and gain 2-3 inches of wheel travel depending on the angle of the A-Frame.

Just remember that with airbags the spring rate is a function of air pressure inside the bag.

Mike
 

ntsqd

Heretic Car Camper
Spring rate and rated weight capacity aren't the same thing. The 2600 lbs rating is likely at maximum air pressure, which would be the highest spring rate setting. Where the spring (of any type) is placed in the linkage determines the maximum load on the spring. With a poorly placed spring it would be possible to exceed the weight rating with a 1000 lbs gross weight trailer.

In considering the linkage design initially it is easiest for me to think of the spring as a fixed rate like it was a coil spring rather than the adjustability offered by the air spring. That helps me get the basics down first. Then I complicate it.....
 

G-force

Adventurer
Well remember that wheel travel is governed by where you put it on the A-Arm. The closer to the pivot the more travel you will have at the wheel. 2 inches farther up the A-Arm the 7 inch bag will have the same wheel travel as the 8 inch. Knowing that I think I might be tempted to go with the smaller diameter of the 2500. Still plenty of weight capacity.

Arrest me, if i am misstaking here :eek:

By moving the air bag in on the A-arms, the diffrent loads on the arm and bushings is about to change rapidly?

Lets say that the bag is installed 4 inches in on the arm, with the spindle still at the end of the arm. As the spindle moves up, the bushings at the other end, will be forced downwards due to the "up side down, see saw effect".
In my mind, this is something we do not want! I can not see any situasjon where this is a nessesary option ,rather than selecting the "right" bag, for the "right" install on the A-arm IMO. Right on top of the spindle.
 

ntsqd

Heretic Car Camper
Arrest me, if i am misstaking here :eek:

By moving the air bag in on the A-arms, the diffrent loads on the arm and bushings is about to change rapidly?

Lets say that the bag is installed 4 inches in on the arm, with the spindle still at the end of the arm. As the spindle moves up, the bushings at the other end, will be forced downwards due to the "up side down, see saw effect".
In my mind, this is something we do not want! I can not see any situasjon where this is a nessesary option ,rather than selecting the "right" bag, for the "right" install on the A-arm IMO. Right on top of the spindle.
If you look at any 70's era GM front suspension design it places the spring on the lower control arm, inboard of the spindle/upright. That is the same thing as what you're describing. It is not an inherently bad idea at all. Like any possible design that could be chosen it has it's strengths and it's weakness'. Pick the design that has the most desirable traits that you want and the least of your undesired traits. What is "Right" for your trailer may or may not be "Right" for mine.

In this type of design you're using the control arm as a lever to increase the wheel travel beyond the travel of the spring. In doing so this drives the actual spring rate to be higher to much higher than the effective wheel rate. Just a different set of compromises.
 
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