Before you youngsters start getting the wrong idea, remember those parts were chosen not purely for their weight, but because they were the top-of-the-line stuff available then, for their weight. There were no splined hubs, Miyata made the best seats, etc. The biggest drawback of my Roger Davies frame is the measurement between the fork legs. Fat tires don’t fit! Nobody was using them at the time, either. So my carbon MUni, with 26" wheel, remains one of the lightest unicycles in my collection.
There was a Japanese guy with a gorgeous, monocoque carbon unicycle at Unicon IX in Germany. The thing was gorgeous; a work of art. Aluminum seat post, handmade bearing holders and cranks, and a carbon hub. The crown and legs had a cross-section like an airplane wing. Sweet! Someday I’ll have to scan those pictures…
So Tour de France riders all have carbon. What’s that got to do with us? Though a few of us have unlimited budgets, there still needs to be a market for someone to produce anything in decent enough amounts for it not to be astronomically expensive. That’s what I meant earlier. The guy with the carbon uni at Unicon IX told me it cost him roughly the equivalent of a “small car” in his limited English.
Well, in materials, cf isn’t extremely expensive, but forming it into the proper shapes that will give a signifficant weight advantage and still be strong is a very long and expensive design process. Also someone who shells out such a large sum of cash for a frame would also likely expect it to be at least as strong as any frame out there, uping the R&D costs more. Another thing is cf has poor resistance to repeated stress, worse than aluminum, and as someone said breaks before bending and all the UPD’s would wear it out as well.
Not that it can’t or shouldn’t be done. It’d be cool to see a well made cf uni and how it compared to other frames.
Material Density (g/cm^3) Stiffness (GPa) Ratio
4130 Steel 7.85 205 26.11464968
Titanium 4.506 116 25.74345317
Aluminum 2.7 70 25.92592593
CF 1.75 150 85.71428571
Ok, ok. I know you asked for the weight, but I figure what you really wanted was the density, since you didn’t specify an amount of each to give you the weight for
However, keep in mind that the structure of the frame contributes as much or more to the weight of the frame than the density alone. For example, steel is quite stiff, stiffer than either aluminum or titanium, so you can use less material to make a frame of similar stiffness, while it takes something like twice the amount of aluminum to make a frame of similar stiffness.
What we should define for these framebuilding questions is a density to stiffness ratio. On this basis, CF is best, followed by steel, then alu, then titanium. Factoring in strength makes it more difficult, because that varies with strength treating and alloying process, as well as with the amount of material used.
Carbon fiber is just what its name implies… it’s a fiber, thinner than a human hair. Like fiberglass, carbon fiber is woven into a lattice-like fabric which is then formed and set into plastic. This material is then called carbon fiber reinforced plastic.
Note: this material isn’t “solid CF” it’s merely plastic with embedded CF fibers.
As I’ve pointed out many times before on these fora, CF’s strength exists only along the length of the fibers. In a fork or a uni frame, the fibers run the length of the legs, to support the weight of the rider. Any impacts on that frame would apply force along the sides of the fibers, where they are the weakest… and this is why a CF uni frame must be handled with care.
I’ve never bought a witch before but I’ve seen witch costumes for sale for about the price of a pair of pedals.