Frame Type and Material

What kind of and from which kind of material?

Strength compared to weight and these compared to price are the most important criteria when choosing what kind of material the frame will be. Carbon fiber composite, aluminium, steel or something else? Where could we get it, how much it would cost and what kind of manufacturing process is related to it?

Carbon fiber composite, in other words epoxy mass with carbon fiber. Also often fibers are set so they are in same direction with the maximum forces that will affect to the object. Relatively very expensive material. Carbon fiber composite is very likely the best material for motorcycle frame today if we look the issue from the strength to weight ratio aspect. Then why is the carbon fiber so strong? Carbon is an element which has many states, one of this is in diamond. In diamond carbon is organized so that every carbon atom is very hard onto with its four adjacent carbon atoms. Carbon fiber is very strong if the operant force is in line with it. For example carbon fiber made skiing stick is light and strong if we are skiing but if we are fencing they will broke. At this moment they are using carbon fiber composite in Moto GP -motorcycles and Formula 1 -cars. Why didn't we choose carbon fiber composite then? Well we have a strict budget and we could't afford it. Also manufacturing process is little bit unfamiliar, this would spend our other resource, time. Compared to steel frame we didn't came to result that would favor carbon fiber composite, even if we would had been able to design and manufacture slightly lighter frame with it. It would had been so much more expensive in time and money that it would had not been the best way to go to our goal.

Aluminium casted is probably the most popular choice for motorcycle frame by manufacturers. This is in series produced motorcycles and in race motorcycles. In Moto GP they are moving to carbon fiber composite. Ducati is showing the way. But in series produced motorcycles aluminium casted frame will stay awhile. These things proves that you can build a very good and in mass production scale cheap frame using aluminium casted frame. The inexpensiveness in mass production scale is because of it's expensive to manufacture cast but when it's done, manufacturing one part is very cheap. By this reason this kind of frame is not suitable for our project. Welded aluminium tube frame is not better in strength to weight ratio than welded steel tube frame and it's more expensive and more difficult to manufacture. This because aluminium should be special kind of aluminium so that its welding qualities and strength to weight ratio would get better compared to steel.

Triangle geometry followed by high strength steel tubular frame was the choice where we ended up.  Rautaruukki had suitable steel for our frame. Form600 high strength steel tube has yield strength of 500 MPa and breaking point of 600 MPa, it has very good welding qualities and weight is no more than, maybe the most used, steel S355 has. About 8 kg per liter. With triangle geometry it's possible to design very light and strong frame. Along with these reasons, one reason was that Rautaruukki sponsored the tubes to us.
 
If you are building frame from steel, the best way to go is tubular type of frame. Different kind of solutions has been seen like in old GSX-R:s. In Moto GP there was steel tubular frames in Ducatis motorcycles before they went to carbon fiber frames at 2009. Below simple example of the firm idea of triangle geometry.
 

So the structure is closed from left upper corner and it's pulled by force showed by red arrow. This force cause forces that are showed by yellow arrows. Theses forces cause structure to deform and if the force is strong enough the structure will brake. If we place support showed by right picture, structure becomes considerably stronger compared to its weight. So the foundation of the idea is very simple.