Bonded carbon tubes on aluminum frame
 

Has anybody ever tried to replace any of the tubes on an aluminum bike with carbon fiber tubing? I'm talking about say an old Cannondale with a damaged downtube, would it be possible to replace the down tube and maybe others with carbon tubes? Years ago I really wanted a Trek carbon fiber bike. A friend of mine had one, I think it was a 2300 might have been 2400 or 2500 I think it had Shimano 600 components. I wanted one but didn't have the money. I inquired about just buying a frame but the cost was almost as much as the entire bike. Anyway, I like the idea of mixed materials and I always loved the looks of the aluminum and carbon frames. Specialized made one too and I'm sure several other companies did too. So I would like to make one out of an old CannonDale or I could buy a different frame but I wouldn't want to spend too much on my first try. So if anybody knows anything about doing this please let me know. I've searched different sites and I have never seen one online. I have no experience with carbon but I have worked a little with fiberglass.

Thanks,
Ben Voiles

I haven't tried what you're proposing, but when we were developing the Trek bonded carbon/aluminum frames, we had to put fiberglass sleeves in the joints to insulate the carbon fiber from the aluminum because of concern for galvanic corrosion.

Something to keep in mind, anyway...

That is sure interesting. At Yeti we used a permabond product first then someone from Trek contacted us with info on Hysol products.

Carbon and aluminum don't play nice with each other. Don't try it.

An easy way to deal with the galvanic issues and to improve the bond integrity is to use phosphoric acid anodisation on the aluminium and pre-impregnate the anodisation (which is porous) with a low viscosity laminating resin. Measurements made on PAA layers I've made indicate excellent isolation can be achieved easily.

My problem with the OPs proposal is that the ends of the Al tubes were not designed as sockets for bonding.

I would take a peek in THIS thread. There was some talk about galvanic corrosion.

The first problem that i thought of was the mechanical fitting of the carbon tube in/over the Alu. tube ends. For sufficient bonding over lap to exist the Alu frame would have to be sprung apart a bunch. Not what I'd want to do to a thin wall Alu structure. You might end up needing to replace far more tubes then only the down tube.

I remember when Specialized came out with their Stumpjumper frame set with TI and carbon construction. They said they had to, basically, build the frame twice. The first time with the TI tubes then cut that down and then the second time with the carbon tubes bonded to the TI joints.

The push to create the all carbon frame (BB shells, head tube bearing seats and drop outs) is for light weight to a degree but also to eliminate the bonding/galvanic issues of mixing metals and Carbon. There are wonderful methods to treat/prep the bonding surfaces to produce no galvanic issues and long term durability/strength but when the production is taken out of the prototype facility and done in the production factory by workers that are being paid to be as efficient as possible the processes can slip. Andy.

7000 series aluminum especially..


Ben , I suggest cutting the damaged aluminum frame tube out,
so No One else is hurt trying to rebuild a dumpster find, and getting new stuff.

I've thought about this to drop weight on the rear of the bike.

I have a Rocky Mountain Solo 50ac, which is an aluminum frame with a carbon fiber rear triangle. Its a factory built frame. I have never seen any galvanic corrosion on it. Maybe you can email Rocky Mountain about their process. The feame is out of production.