Bicycle Mechanics - carbon fiber frame

i was wondering how thick are the tubes on a CF frame bike? i'm mainly interested in mtn bike frames, not road. what kind of compound are the carbon fibers impregnated with?

i am asking because i am thinking about building my own frame from the ground up. hoping to pick up a cheap frame, chop the tubes, then replace with carbon fiber tubes, using the headtube, BB, and seat junction as "guides" for my homemade carbon tubes... that way i can define my own geometry somewhat. does this seem feasible? why or why not?

give me some feedback or links where this info can be found. thanks in advance!

Originally posted by tFUnK
i was wondering how thick are the tubes on a CF frame bike? i'm mainly interested in mtn bike frames, not road. what kind of compound are the carbon fibers impregnated with?


Carbon fibre frames can be impregnated with a variety of different types of fibres including aramid, kevlar and even titanium. These are further classified in terms of tenacity and modulus. Trek uses high-modulus fibres for instance whereas my Aegis is made with intermediate modulus fibres. Also, there's the type of epoxying. Generally speaking, CF bicycle frames are made with either thermosets or thermoplastics. My mountain bike's main frame is thermoplastic but the swingarm and fork legs are thermoset. As to the thickness, that's very dependent on the manufacturer and the section of the frame. Many frames are not of consistant thickness.

That's one of the craziest things I've ever heard, but I like your style. :beer: I know of a guy who actually did spend time working in the aeorspace composites industry in Colorado...built his own monocoque carbon MTB. I haven't had a close look at it, but believe it IS FULLY FUNCTIONAL and reasonably impressive to look at. I think a one piece 'monocoque' frame has a better chance of success in terms of weight/strength/reliability and ease of setting your own dimensions. I believe that is how Kestrel make their frames, and it makes much more sense structurally than glueing tubes to alloy lugs, like OCLV Treks. No doubt Trek have their reasons....cost?

Incidentally, if the US Postal team uses standard OCLV frames, can anyone confirm a single frame lasts each rider an entire season? Crash damage excepted of course. (Oh, the claws are out now!:p )

Look at the merlin Cielo it is titanium and carbon fiber. It's a absolutely beautiful bike!!!

I've got nothing against those new carbon rear Ti and Al bikes. They're very nice. Not that any bike is indestructible anyway, but putting more carbon on a Ti bike does seem to take away a little of its ruggedness. And by the time you've got carbon fork/steerer/seatstays, why not go the whole hog with a Kestrel carbon monocoque...if you're already spending the $ on Ti anyway? Tho, must admit, all my scratches and dings are on chainstays and top/down tube. Would gladly park a new Lightspeed Ultimate in the garage. :D

Carbon is pretty mushy and unresponsive, IMHO. I've ridden the 5200, Kestrel (ridiculously flexy laterally), Look KG 381, and Colnago. Ti is where it's at.
Your idea would be pretty cool if you really want to do it and can pull it off.

Carbon, Ti, Aluminum, Steal they all will ride differently depending how they make the frame. I don't think you can make a blanket statement about any material a frame is made of. You can make generalization taht aluminum is harsh and steal has a more comfortable feel but this is not always true.

One leg and two angles define a triangle. If you're planning to use a head tube and stubs from the top and down tubes as a starting point, you're not going to change the geometry very much.

Originally posted by Spoke Wrench
One leg and two angles define a triangle. If you're planning to use a head tube and stubs from the top and down tubes as a starting point, you're not going to change the geometry very much.

that's very true. while i can maybe bend the tube a little bit to change geometry, another problem would be dependably securing the carbon tubes to the headtube without it falling off.

the carbon idea may be put on hold for a little while (i was going to do it to the specialized m2 frame that already has a chopped top tube); i just acquired a what i believe to be tange stumpjumper, with some rust and painted black. looking to strip the paint and try to fix some of the rusting, then painting it, following a route similar to Kev's mirage project =]. it will be used as singlespeed.

we'll see how it goes, i'm still itchin' to mess with carbon fiber though...

while i have no idea as to the practicality or feasability of such a product ... make sure you wear an adequate respirator if you sand/cut that stuff...breathing it is not so good for you

i have heard the dust can be irritating to the skin as well

Have a read of
http://www.sheldonbrown.com/rinard/

Damon Rinard has addressed most of the problems of home CF construction, including safety testing, alignment, corrosion and fittings.