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Hi All,

My goal is to find a standard product CF tube which could reach the E value and the compressive strength of mild steel.

I can find plenty of tubes that you make, but none have the needed information to make a decision, so I have attached a design document showing the requirement.

Hopefully help is close.




For front push rod              -find Ixx for worst case load, 15660 N cornering,  with SF = 2


S.F of 2 to reach YP of MS = 250 MPa t & c, 150 MPa shear. For pure compression τ max = ½ axial stress

A = F/σ = 15660/125        = 125.3 mm2      

Tube dia = 25.4 mm , circ = 79.8 mm find thickness.

A = Pi*r2   t = A/circ = 125.3 /79.8 = 1.57 mm            (1x1/16”  25.4 x 1.57mm)  Ixx = 8350 mm4 (stress limit)


Pcr         = π2EI / l2             (pin – pin ends)


Steel      = π2 *207000*8350 /11002

              = 14100 N (= S.F 0.9)        not ok    2.3 Kg (bow & ball joint eccentricity of less than (0.035”) 0.1%)


(1x3/16” 25.4 x 4.78mm)  Ixx = 17300 mm4

= π2 *207000*17300 /11002            

= 29210 N (= S.F 1.86)      just ok   2.67 Kg


(1 ¼x1/16” 31.75 x 1.65 mm)  Ixx = 17700 mm4

              = π2 *207000*17700 /11002 

              = 29855 N (= S.F 1.9)        just ok   1.32 Kg  higher drag


(1 ¼x0.083” 31.75 x 2.11mm)  Ixx = 21600 mm4

= π2 *207000*21600 /11002 

              = 36470 N (= S.F 2.3)        ok          1.73 Kg higher drag


Ti 1.31x0.065”    E=114 GPa          YP 1100 MPa                             

= π2 *114000*36200 /11002                     

              = 33660 N (= S.F 2.15)      ok          1.73 Kg higher drag, ($300/tube)    no benifit


Al (1.25x0.125” 31.75 x 3.175 mm, max wall) Ixx = 29400 mm4      E=69 GPa    YP 275 MPa          

= π2 *69000*29400 /11002  (6061 T6 tube)

                            = 16540 lbf (= S.F 1.06)    not ok    (0.8 Kg) higher drag


CF ???

My goal is to find a standard product CF tube which could reach the E value and the compressive strength of mild steel. Then  the 31.75 x 1.65 mm size would be ok and the weight would be much less.


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As we don't have specific data for compression on our tubes, and our tubes are all manufactured differently for different performance requirements, we can't give you a perfect answer for you. However, we can tell you that Intermediate modulus tubes will give you the best performance for tensile strength and stiffness, which can come in handy in compression situations as it will deflect less and be less prone to failure. The image attachment below will give you an idea of the different properties that can be obtained from different materials. AS you can see, intermediate modulus carbon fiber has the best overall performance when it comes to stiffness AND tensile strength.

If I read your inputs correctly, you have a 25.4mm tube (ID or OD?) and a 1.57mm wall thickness. Is that correct? 

As a word of advice, the thicker the carbon fiber tube, the better the compression. Even if you double the wall thickness, you will still be much lighter than mild steel.

Here's a couple tubes to consider. All are IM carbon fiber, but nothing over 1.6mm


As an option, here are some standard modulus tubes with a few more options for thickness.


Screen Shot 2023-07-06 at 10.45.57 AM.png

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