cannondale donor bike

[agentmjq]

I'm a newby and wanting to convert a cannondale R600 racing bike into a very fast crusbike. I've emailed John who indicated I need to be careful that I don't weaken the headtube area. The frame is aluminum with a carbon fiber fork and shimano 105 components. I will need to cut off the top tube, lower a portion of it to fit the seat onto, and re-tianglate the rear triangle. I plan to beef up the headtube with aluminum plates on each side of the headtube. In addition, I plan to put aluminum plates on each side connecting the down tube with the seat tube.
Has anyone every tried this or have any advise before I take a saw to a good cannondale racing bike? An expert tig welder who fabricates race cars will be doing the fabrication.
Indiana Jim

 

[Mark B]

I'd be real careful with this... I'd do some careful research on this because the last thing you want is to have that come apart on you while screaming down a hill. I'm sure you know that when aluminum goes, it does not give much warning. Sounds a little scary, to me.

Mark

 

[defjack]

What size frame is it? You dont want the seat base to be more than 29 in high. 24 is better. The R600 looks way too high to me. Jack

 

[agentmjq]

The frame is a 56. Used as a regular bike it is too big for me. At 5'8" I need a 53, but that is beside the point if i convert it. I could extend the wheel base some by extending the aluminum plates that extend from the down tube to the seat tube.
My intention is to make a converstion that will look similar to the Silvia, bracing the headtube. I could wrap the finished frame in carbon fiber for added strength. I just don't want to end up with a cannondale cruzbike that cost me $10,000 and breaks. I've already got enough scars and scabs from prior crashes. Road rash and I don't get along to well.
You input and thoughts are appreciated.
Jim

 

[Mark B]

agentmjq wrote: The frame is a 56. Used as a regular bike it is too big for me. At 5'8" I need a 53, but that is beside the point if i convert it. I could extend the wheel base some by extending the aluminum plates that extend from the down tube to the seat tube.
My intention is to make a converstion that will look similar to the Silvia, bracing the headtube. I could wrap the finished frame in carbon fiber for added strength. I just don't want to end up with a cannondale cruzbike that cost me $10,000 and breaks. I've already got enough scars and scabs from prior crashes. Road rash and I don't get along to well.
You input and thoughts are appreciated.
Jim

I actually toyed with a similar idea with my conversion bike. It's made with pretty thick aluminum, so it's chunky. I was thinking about shortening up the downtube, then drilling two inch holes all over to sort of honeycomb it. Then, I was going to wrap the whole works in CF. It all harkens back to the notion of turning a sow's ear into a silk purse..

Getting back to your project; I think it would make more sense to do a prototype with a steel frame, to see if it's even reasonable, before cutting up your C-dale.

Mark

 

[Doug Burton]

I would reiterate Mark's idea of prototyping this in steel, which is much more forgiving, before potenitally destroying the aluminum frame.

A couple of things that have stopped me from working in aluminum and CF:

1. Welding aluminum puts all kinds of interesting stresses in the tubes, and the heat affected zone around the weld ends up being quite weak unless the frame is heat-treated after welding, which requires a big ol' oven ( I haven't found anyone around here who can do it.). To insure the frame doesn't distort during heat-treat, it will need to be secured to a steel fixture that doesn't distort at around 400 F. These issues don't show up in racecar fabrication because the parts are usually much thicker than the tubes bicylists work with.

2. Aluminum does not like to flex, and has a finite cycle life before it absolutely will fail. This is why aluminum frames are very carefully, rigidly triangulated or massively over-built. If the headtube is not properly reinforced, it will break off as an assembly. To see how these reinforcements are executed, look at the Sofrider headtube attachment.

3. CF forks do not respond well to point-loading. The triangle brackets that adapt the rear wheel to the front fork will apply cyclic pressures to the front of the fork leg, which will eventually work their way through the CF unless you mould an attachment into the fork leg to distribute the load.

My conclusion after looking at this type of project was that I would have bought the Silvio at least once in project money before getting this near completion.

Hate to throw a wet blanket...

 

[Mark B]

Hardtailcruzer wrote: 1. Welding aluminum puts all kinds of interesting stresses in the tubes, and the heat affected zone around the weld ends up being quite weak unless the frame is heat-treated after welding, which requires a big ol' oven ( I haven't found anyone around here who can do it.). To insure the frame doesn't distort during heat-treat, it will need to be secured to a steel fixture that doesn't distort at around 400 F. These issues don't show up in racecar fabrication because the parts are usually much thicker than the tubes bicylists work with.

I was going to mention that, too, but didn't know enough to write intelligently about it... That's what I recall.

Hardtailcruzer wrote: My conclusion after looking at this type of project was that I would have bought the Silvio at least once in project money before getting this near completion.

Hate to throw a wet blanket...

Yeah.... that, too. I'd still like to try and play around with CF someday...

Mark

 

[JonB]

Hardtailcruzer wrote: I would reiterate Mark's idea of prototyping this in steel, which is much more forgiving, before potenitally destroying the aluminum frame.

A couple of things that have stopped me from working in aluminum and CF:

1. Welding aluminum puts all kinds of interesting stresses in the tubes, and the heat affected zone around the weld ends up being quite weak unless the frame is heat-treated after welding, which requires a big ol' oven ( I haven't found anyone around here who can do it.). To insure the frame doesn't distort during heat-treat, it will need to be secured to a steel fixture that doesn't distort at around 400 F. These issues don't show up in racecar fabrication because the parts are usually much thicker than the tubes bicylists work with.

As far as i know, welding aluminum also releases all kinds of toxic fumes.