ArgoMan

Hey all. I'm seeking opinions regarding frames that use a mix of carbon and alloy parts. I recently built up a Fuji Roubaix frame for my son. It's a mix of aluminum and carbon seat stays. I recently saw a video with an English carbon frame expert who advised that it's a bad idea to attach carbon components to metal components in a frame. The reason is that the metal will expand or contract with temperatures, but the carbon will not. This, he argued, stresses the areas where the carbon and the metal are joined, and that they eventually will separate at those areas. I see the carbon/metal combination with a lot of forks. I run such a fork on a bike, where the steerer tube is aluminum, but the lowers are full carbon. I imagine lots of us have forks of such construction. This worried me, as I live in the desert where we get extremely high temperatures. I was also thinking about buying a new frame made of high-end steel, but with carbon seat and chain stays. Now I'm wondering if that's such a good idea. I'm also worried about my son's bike falling apart! Does anyone have any perspective on this issue? Thanks!

wheelreason

They add nothing, and introduce potential issues, so while not inherently bad, no real reason for them, but like anything else there have been good and ones that don't identify as good examples....

VegasJen

I havea K2 with mix carbon/aluminum front fork and carbon seat stays. K2 stopped with hikes more than a decade ago but I have had no such issues with mine. I don't put a crap ton of miles on it but it's at least 10 years old, maybe 20. And I also live in the desert. No signs of delamination on mine. I'm sure it can happen, just like anything else, but I suspect we're talking about many, many years and many, many miles.

Iride01 

It depends on the design. So no one right answer. There was a bike back in the early days of CF that was made from carbon fiber tubes fastened together in metal lugs where the tubes transitioned from top tube to head tube and seat tube to top tube. And etc. It was a bad idea. Maybe not so much for the lugging. But just poor understanding of the technology used in it's day.

Carbon fiber fork blades have been common in many aluminum and steel bikes for a while now. And they don't seem to have any issues.

Kontact

My perspective is that the "english carbon frame expert" is not an expert. This type of manufacturing goes back to the '70s for bikes and earlier for aircraft. It isn't a problem.


He might have mistaken galvanic failures for this, but that is caused by improperly designed frames that don't have any fiberglass between the aluminum and carbon. Which good manufacturers have been doing since the beginning.

Camilo

I have a Jamis Nova Pro frameset - I'm not sure how old, I got it used about 13 years ago and it was a couple of years old at that point. Through 3 or 4 different builds it's still going strong.

Full carbon fork, aluminum triangle and chain stays, carbon seat stays. It's always been a comfortable bike, but I think that has mostly to do with running 38mm tires and having a good fit on it.

I look at the stay-frame joints every once in a while and haven't seen any evidence of failure.

terrymorse 

Calfee Design, one of the pioneers of carbon frame building, has an "interesting" white paper that covers the problems when joining carbon to metal:

Calfee Design: Technical Paper-Materials

See section 4: Interfacing Carbon with Metal Parts

Kontact

It's a little self serving, since he doesn't even mention fiberglass cloth which is commonly used on this kind of interface. It's more a statement of his preferences.

tFUnK

From a manufacturing perspective joining carbon to alloy can be less sound than doing a full carbon frame but in practice I'm not sure if the end consumer will experience shorter longevity with the former. In theory yes the interface between alloy and carbon can be more likely to fail than full carbon but that's not saying they all will fail. Reputable frames should pass quality standards regardless.