Safety Review of S3, Ultrafoco, or EOM tubes?

What are your thoughts on the new thin S3, Ultrafoco, or EOM tubes? Anyone know how safe this stuff is to ride? Some of the butts on these tubes are .5mm!!!! I know there are some other racers in this forum.

 

Bit of an age old argument there - it's not the tubes, they're plenty strong - it's the craftsmanship of the guy putting them together ! You'll find that some of the best builders will actually mix tubes from different sets to better suit a particular rider or frames at the large or small end of the scale. If you're careful what you buy I don't believe it's a problem in any way. The durability issues that some people may argue about are, again, not about the tube runs but the areas of tube joins and the quality of the tube end profiling and welding/heat treatment.

 

No doubt that the framebuilder makes a big difference, but I need to find some opinions on the reliability / durability / stiffness of the tubes themself.

 

The idea behind thin tube walls is that a thin member can carry a great load in tension, whilst a member with a bigger moment of inertia (generally bigger in diameter) will carry better loads in compression.
The moment of inertia is proportional to the fourth power of diameter of the tube and the weight is proportional to the second power of diameter. So if you make a big enough cross section of tube then you can reduce the thickness of the material to the point that the amount of material used is less!
The smaller thickness (0.4mm in some cases) of tube wall usually only occurs at the point between the tube ends whilst the end sectins themselves are thicker (2~3mm) to give a bigger area for welding.
The problem in the past has been that thin walled tubes have been difficult to extrude due to the internal grain structure of the materials. But as alloys have improved, grain sizes have dropped and thinner walls have become more possible without loss of strength.
The only safety issue I can think of with this material is that the tube is so thin that it is easily dented or even torn! However anyone who can accidently tear through a steel tube doesn't deserve a nice bike in the first place!

 

Yeah, but is .5mm butts going to hold up over cobbles?

 

You don't trust me do you?
OK The CSC team uses Cervelo Soloist and Super Prodigy bikes for most of their races this year. Andrea Tafi and Tristan Hoffman used the Super Prodigy at this year's Paris - Roubaix. The Super Prodigy is constructed of a custom extruded Columbus Ultrafoco tube set with wall thicknesses as thin as 0.38mm. Why do i use these two riders as examples? Because Tafi weighs in at well over 90kg, is about 6'6" (I have met him) and both he and Hoffman are known as big gear grinders (they used 46tooth small rings!). This means that they place higher forces on a frame than you or i could ever hope to. i would have thought that this would be proof positive for you.
If you still don't get it then try this.
Doing a static analysis of the frame itself reveals that the top tube is under tension and -as I said before- thin sections can be loaded highly in tension. It is usually only the top tube that is this thin. You will notice that wall thicknesses vary between the down tube, top tube and stays etc because they are all loaded differently.
If you STILL don't believe me then take a look at Starship Aluminium. It has wall thicknesses of 0.6mm and Aluminium is significantly lower in strength than Steel.

I am a Mechanical Engineer and I obviously don't have the room to explain all the theories and maths behind what is a simple analysis. If you look at a bike frame as a truss with forces applied at the seat and wheels then it is easy to analyse. Any basic statics text book should be able to explain this well enough.