split back-bone


Scroll down for some pics of a Norton featherbed frame


The Norton Commando is a notable exception, but that was spoilt in two ways, one;-- the backbone could have been larger, and two;-- the potential stiffness from this frame was thrown away by the method used for rubber mounting the engine AND swing-arm. Probably the main reason for its lack of use in production, is that on a large bike the space needed for the engine, airbox, battery, etc., is not compatible with the concept in most cases. The flavour of the month frame, at the moment, is the twin boom type (Delta box and the like), this can be considered almost to be a split back-bone which gives more room for the engine. Like the back-bone it can be quite rigid if done properly and I see it as a significant improvement in mass produced frames. I only hope it survives the ever present demands of fashion, which often dictates change for the sake of it. If you have any of the above types of frame it is unlikely that you will need to think in terms of modification to improve it's stiffness. As they are more common, it is likely that you have some form of multi-tubular frame consisting of a number of medium sized bent tubes, descended from the previously mentioned Manx Norton.
http://www.tonyfoale.com/Articles/Frame.mod/KawaMods.htm

also double backbone

I know a few custom builders who are taking this direction. They take a big American V-Twin and stuff it into a sport bike chassis that they hand fabricate. But it’s always for a one-off project. As the opposite, the idea of Curt Winter, owner and designer of Big Twin Racer, is to offer a ready to assemble aggressive riding style sport bike chassis accepting most of your Big Twin components. So he designed a rubber mounted frame with increased longitudinal ridgitity by the use of a unique perimeter style double backbone.
http://www.cyrilhuzeblog.com/2007/07/06/ever-dreamed-to-chan...

also
twin-tube backbone frame
The engine is bolted into all-aluminum twin-tube backbone frame that arches over the engine rather than around it, as with conventional sportbike designs.
http://www.motorcycle.com/news/news1513.htm

The backbone is also called spine


Some more stuff one frames

Frame Introduction


In the early days little engines were fitted to bi kes and declared motorcycles luckily we have come a long way since. The first pure mc frames were built from thin steel. Later the steel was pressed to give it more strength. The major battle of Japanese manufacturers to build more powerful engines left many frame too weak to handle them resulting in wobbly / weave riding characteristic.


As more strength was required from the frame, steel tube designs were introduced with the Norton Featherbed leading the way. The steel tubes were then triangulated to form a strong complex web in which the engine would rest. Later development saw the engine become a member of the frame as the steel tubes were linked with the stability of the engine.



Generally a cruiser or custom motorcycle will have a longer frame and the weight ratio more towards the back. This give the motorcycle a slower reaction time, bigger moving space and overall more easy going riding position. Sports motorcycles tend to have a shorter frame and the weight more forward. This makes the motorcycle steer sharper, react quicker and a more edgy riding style.








Useful Frame Tips

You'll find the following types of frames: classic steel tube cradle frame, large main spine frame, ladder of thin tube frame, twin aluminum spars frame.

Frames are made to be stiff, if a frame flexes the wheels aren't in line anymore and the steering goes bad on you.

Frames get most of there strength from the material used, form of the tubes, the structure of the tubes and reinforcements.

Single cradle frames explained - have a main backbone above the engine with one (or two) down tubes in front of the engine. Additionally the frame surrounds the engine with a sub frame going to the back.

Stressed engine frames explained - the engine become part of the frame (saving weight and space) additionals are bolted on to the frame, together it creates a stiff chassis.

Backbone frame explained - the engine sits below a top frame bar (tube). This kind of frame is mostly for smaller engine motorcycles

Diamond frame explained - a single tube hangs down from the backbone on which the engine is bolted, only then does it form a complete chassis for the motorcycle. Mostly used for smaller engine motorcycles.

Frame Rake explained - refers to the steering head angle which often is the same as the angle of the fork tube angle.

Frame Trail explained - refers to the travel distance of the wheels / frame. Said simply - the shorter the trail the more direct a motorcycle steers.

Wheel base explained - the wheel base of a frame refers to the distance between the wheel centers. (overall length of a bike is the distance between wheel ends)

Periodically check all bolts on the frame (frames don't need much maintenance) but do check all bolts often, you'll be surprised at what comes loose over time.

Over time the motorcycle (frame) might feel a little unstable this is often caused by worn and loose bearings (e.g. a clunk in the steering, drifting in a straight line, vibration in the bars, etc)

Anytime you are dealing with a motorcycle from a crash the frame will need to be checked. That's an expert’s job…really take care of getting into repaired damaged frames.

Frame maintenance should be a regular part of your service schedule – check swing arm bearings and linkage – lubricate swing arm and bearings – Check steering bearings – check nuts and bolts.
http://www.best-motorcycle-gear.com/motorcycle-frames.html