Hi Bruce, I just had a look at the CST website, compared their tube dimensions with their stated EI (Flexural stiffness) values, their EI values come in quite a bit lower than those for the same dimension tubes from either
C-Tech or a
carbon tube manufacturer in the UK.
My calculations based on (what I think is standard) 87 - 95 GPa carbon match exactly the quoted values from the later two manufacturers, but the stiffness values quoted by CST are much lower. (For example I would expect their 38.3 mm ID/1.8 Wall/41.9 OD to have a stiffness of 3.97kN.m^2, but they quote this tube to be only 2.9kN.m^2)
Only thing I can think of is their carbon is a lower specification (by about 30%, modulus must be about 63GPa, not 90GPa) than what C-Tech are using, or possibly a carbon-glass mixture. If this is so, we'd need to take that into account when specifying what is needed, possibly go up one more size.
Sorry for all the numbers/weird terminology, hope it all makes some sense. I'm also not trying to persuade you to go the carbon route, just make sure that we get it right if you do.
Ian