Cannondale P-bone

P-bone is an extraordinary product, extremely sturdy in design.

An opportunity presented itself, so I went ahead and bought one because I didn’t have enough money to buy a suspension forks. There is one important difference between a suspension forks and a P-bone, P-bone bike gives you a special adrenaline rush, until you fall off the bike that is, which will happen a lot.

The product itself is made from aluminum pipes the likes of which one would normally find used in a bike frame. Steerer is made of steel and the whole thing weights only 900g. This is extremely lightweight for something that can withstand a Nuclear™ Blast®.

This is how the P-bone forks looked like when it was brand new, later on it got a bit charred. Smiley

The biggest flaw in this forks design is the missing disk supporter. You can see one of my inventions further down; a carrier which would enable me to break safely (without falling). I never made that idea into reality because I fell off the bike so hard I couldn’t walk for a while and was left with 3 huge scars to remind me of the fall. I broke nothing but I still decided to buy a different type of bike forks.

The first drawing of the disk break adapter.

The drawing of the adapter.

A drawing of of how the adapter should look like after being successfully mounted on the bike forks, in relation to hub and disk rotor.

Let’s get one thing straight right away, having a sturdy forks is a wonderful thing, it enables you to reach high velocities, but if you fail to use it correctly you won’t get a second chance. The forks doesn’t forgive or forget; it doesn’t allow for any mistakes to be made, it is painfully rigid. The pipes are completely vertical to the ground, and that is painfully rigid (literally). Your will feel shoulder strain from excessive use.

Although the adrenaline rush on a P-bone is amazing, one cannot escape the feeling that as soon as one hits a hole in the road, the problems will become apparent. One will not only fly over a cookos nest, but land in it. I tested it a few times on “Sljeme” (hill behind Zagreb) and I got pretty much seriously injured. You do feel great going downhill but as soon as you hit a hole, you’re in trouble. I must have fallen at least 20 times. One time I was driving downhill at about 40-50km/h when I hit a hole, I must have flown 10m through the air in a theatrical flight, entangled up in my bike, having its drive lodged into my left calf, and ended up lending in a pit. That wasn’t a pleasant feeling. Smiley By the way, some time after my fall I had a chance to observe one individual jumping down a 5m slide again and again, watching it requires having guts.

My personal “feelingfull” observation: You could do ok with this configuration, but only in a highly controlled environment (in a town, no holes on the ground) and a perfect driving technique, everything else would be considered too risky.

One other thing, in order not to foil the bikes geometry, I designed an adapter which is to be placed on the bike forks and thus elevate the bike frame to the appropriate height (the adapter itself weighs more than the forks because I made it from an axle I took from a tank).

I left the forks at home, even though I decided to sell it. It simply wouldn’t go away on its own… Smiley Since the adapter was made of steel it got permanently stuck on the forks so I left the whole thing as it was in case I ever needed it again. Smiley (Update 2006. – the forks found a new owner who still uses it.)

While using the aforementioned forks on a Cannondale CAAD3 bike frame I was driving a one-of-a-kind never-before-seen bike. It was a good feeling having a unique bike. Smiley I even had some of my posts removed from mtbr.com for writing about a non-existent bike… Smiley

The schematic for an adapter used to elevate the headset main ring (weightbearer).

The break adapter has to be constructed using a pipe which has to have an appropriate diameter and a rounded P-bone leg 2-3mm thick so that it doesn’t interfere with the rotor. You have to weld a piece of metal on to the one of forks legs, which has a hole the exact size of the disk break clamp. This piece of metal has to be fastened to the forks with 2 screws through a spiral made on the side of the mounting leg, plus – it has to be on the outer site. The whole thing is to be very rigid since you are supposed not to encounter any problems when fitting a rotor 203. The concept is laid out here, the rest is up to you. One other problem you might encounter is the fact that most of the machines used for turning have limited production capabilities and that the person operating them doesn’t want to spend too many work hours on your little project. The production of a very similar adapter would cost somewhere around 200-300kn (that’s about 40 euros, or 50 dollars). Please bear in mind that you really should supervise the entire production process (and know EXACTLY how the final product is supposed to look like once it is done), otherwise you might end up with a faulty product on your hands. The first adapter that had been done was faulty. I wasn’t there during the entire production process so the machine operator misaligned the headset ring which was supposed to fit on the crown of the forks… I mean, they did fit perfectly, but were unusable. Smiley In the end we used adapter #1 to hammer in the adapter #2 Smiley

You can use only a completely rounded forks leg with this adapter, anything else simply won’t fit. You could also weld the adapter on forks made of steel but you would have to take in consideration the tremendous force produced by the break disk.

A picture of the elevation adapter mounted on a bike.

This same adapter can be used on any rigid or suspension forks as a distancer for achieving the desired height, the only thing that can vary is the length of the adapter body. I think that any potential reader should customize this project to suit his own needs, I didn’t need any further customization myself so I haven’t thought one up but I was thinking about using a three piece system that would fit tightly – in that case you would be able to reduce the weight of the adapter by 50 to 70%. The core should be made of aluminum and the rest should be made of steel. You could also make it out of one piece of steel, with cavities, but that wouldn’t look so god.

P.S. The P-bone is definitely bullet proof, I never heard of a single broken or damage one.hehehe

Update 2006. – one more thing should be taken into consideration before starting with project like this: the amount of time, effort and money invested into project will surpass the cost you would pay if you waited for a bit and bought a catalogue quality product.