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  1. Spanish Wells

    Design trailing arm suspension

    Thanks Swinney
  2. Spanish Wells

    Design trailing arm suspension

    Swinney Appreciate the input once again. I believe I understand the notion of compliance. However I'm not sure that I follow how the two systems are so fundamentally different. As I see it, the "g" force is an acceleration; "compliance" in the system slows that acceleration down so that the...
  3. Spanish Wells

    Design trailing arm suspension

    Swinney OK. I went to Engineer's edge and found: "Beam Stress and Deflection equations and calculation for beam supported at both ends and two equal loads" They show the equation: Stress = Wx/Z or Wxz/I for my example, 5" tube, 1/4" wall, 70" long, 42" between supports, equal loads of...
  4. Spanish Wells

    Design trailing arm suspension

    Swinney, Maybe I'm wrong, it's been 45 years since I did structural stuff in college. My point is to try to define what g and safety factor Dexter has used in their design. In the beam axle, 5' OD, 1/4" wall,10,000 lbs load rating. 70" long, 42" between spring hangers, Moment of Inertia for beam...
  5. Spanish Wells

    Design trailing arm suspension

    To continue my argument further, if we add a spring suspension seat into the model, clearly the driver does not feel much of the effect of a large shock load; clearly that is the point of suspension. Whereas with solid wheels, no suspension and sitting directly on the frame the driver would feel...
  6. Spanish Wells

    Design trailing arm suspension

    Thanks Swinny for once again taking the time to contribute. I value your opinion and am certainly considering your input. For discussion: - In my post of 28 July, 13:30, I "reversed engineered" a Dexter 10,000 lb trailer axle to see if I could figure out the loads they are using. If you consider...
  7. Spanish Wells

    Design trailing arm suspension

    LittleInch, You may be correct. 80 ft, include drawbar of 10" x 10" x 3/8 tube = 3,800 (correction, doesn't need to be full length of boat). 00 lbs. 20 ft 4' x 4" x 3/8" cross-members = 340 lbs 6 trailing arm assemblies @ 60 lbs each = 360 lbs 3 complete Dexter 10,000 lb axles @ 435 lbs ea...
  8. Spanish Wells

    Design trailing arm suspension

    Retired, The math has evolved as different solutions appear. The weight of the boat is 24,000 lb, supported on 6 tires. So with the weight of the trailer itself, I'm using a design load of 5,000 lbs per tire. That is the load supported by each tire, and therefore each suspension trailing arm...
  9. Spanish Wells

    Design trailing arm suspension

    LittleInch Once again thanks for your input. I'm trying to avoid having any part of my swing arm arrangement under the trailer frame. The reason for this is that the tire is 32" diameter, and stub axle tube 5"; so that would mean minimum frame height 19". If I then add suspension travel of 10"...
  10. Spanish Wells

    Design trailing arm suspension

    LittleInch Thank you once again for your contribution. I accept all of your points, and it's good to have a conservative point of view, as a challenge to the thinking. Clearly this is a massive structure. Initially I underestimated the loads involved - certainly one of the main reasons I posted...
  11. Spanish Wells

    Design trailing arm suspension

    Retired Thanks for your contributions. The approach you're suggesting doesn't fit my need because to get the overall suspension movement I'm looking for I must have all the components on the out side of the beam. I have seen the style you are looking at, particularly on extreme offroad camping...
  12. Spanish Wells

    Design trailing arm suspension

    Greg, Do you have something constructive to offer ?
  13. Spanish Wells

    Design trailing arm suspension

    Swinny, So, working on your suggestions, and some calculations Retired has steered me towards, here is my thinking: 6 tires, 3 each side on outside of trailer. Capacity of 5,000 lb per tire. Trailing arm length = 14.5" Small bending stress, as triangulated directly to spring. Length of stub axle...
  14. Spanish Wells

    Design trailing arm suspension

    Thanks Retired...
  15. Spanish Wells

    Design trailing arm suspension

    Retired I tried your link, but it won't open for me. Not sure if there is a daily limit on how many times you can enter the site, as a guest, or whether this is in the "not free" area. Thanks Bob
  16. Spanish Wells

    Design trailing arm suspension

    Retired, Similar concept.
  17. Spanish Wells

    Design trailing arm suspension

    Regarding loads to be considered in this design. In theory, the acceleration of the wheel hitting a 6" high curb at 50 mph could be calculated, but this would be quite complex as it needs to include the spring rate of the tire, suspension, and any other member that deflects under this load. An...
  18. Spanish Wells

    Design trailing arm suspension

    Retired Is the link correct ? It comes back to this post. Bob
  19. Spanish Wells

    Design trailing arm suspension

    Swinny, Thanks again for the input. Can you point me to a calculation, or equations for torsion in square tube please ? I've not found anything. Your comment regarding the swing arm being same size as the frame - in that design that arm you refer to pivots to raise the whole trailer some 24"...
  20. Spanish Wells

    Design trailing arm suspension

    Swinny Thank you for taking the time to contribute. I do not want to be seen to be defensive here. Just to discuss your thoughts. My background is a retired Production / Industrial Engineer from the UK, living in the US the last 30 years; working with a major tire manufacturer. I have built...

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