Carbon and Alloy Mixed Frames
 

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!

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....

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.

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.

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.

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.

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

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.

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.

The first frames of this kind I can remember are the Peugeot bikes ridden by Robert Millar for the Peugeot team back in the 80's. The three main tubes were carbon, the fork and stays were aluminuim. There were rumours of issues but there were very few in the hands of amateur riders to know for sure.

There are tens of thousands of carbon/aluminum Trek frames out there and even more carbon/aluminum forks still being made. They aren't exactly rare among consumer bikes.

The ones you refer to are from the Armstrong era, much later than the Peugeot bike which came out in 1984. I would expect design and material improvements in that time. Manufacturers have been playing around with different materials over the decades, largely I think more for marketing purposes than necessity. I had a magnesium alloy bike purchased around 2005, got around 6 years out of it before the frame cracked. I also have a carbon road bike, lightly used for the past 7 years and despite replacing this, that and the other, re tightening bolts etc, the frame makes a ticking noise under load. So from now on I'm sticking to aluminuim or steel. My other three road bikes are entry level alloy bikes and they are smooth as silk.

The only aspect of them that I have a problem with is that they're usually quite ugly. At the least , unattractive.
JMO of course YMMV

The ones I'm referring to came out in 1989 like the 2500. Other carbon aluminium mixes as old as the Peugeot include Look, Vitus Carbone and TVT.

And all of those bikes got their technology from aerospace which is much older.

They do look a bit odd although I'm looking for a secondhand one to try out of curiosity. BTWIN the Decathlon brand appear to have frames like this some of which appear on Ebay fairly regularly.

I'm getting some real action on this thread, which I started almost a year ago. I recently checked out my son's Fuji, as I had to adjust the FD. It's a super nice frame. Very light and responsive. It was actually that frame that made me reconsider obtaining far more expensive "modern" components. I just tuned up my home-built bike and it rides like a frickin' dream. Old Scapin Pro Racer steel frame with all 105 components on nice aluminum wheels and Pirelli tubeless. So nice. It all made me realizes that there's so many cheaper, but quality bikes and frame and components out there. No need to spend big money.

Bonded alu/carbon frames were top of the line in the early '00s before full carbon. I owned a few, including a Kinesis, a KHS Flite 2000 and 720(?) and some other boutique stuff. They all rode great, and I never had any reliability issues. If they can figure out bonding carbon and alu in a demanding application such as aerospace, then they can do it for a bike frame.

Only downside: slightly heavier construction than full carbon. Nevertheless, these frames & bikes now sell for next to nothing, and if kitted out with say, Dura-Ace 7700 or 7800 or Campy Chorus or Record will perform as well or better than any current 'performance' road bike regardless of how much you pay. Performance being measured as speed over long distances and the ability to hang with the fast crowd.

I would not be concerned about the difference in thermal expansion if the correct bonding adhesives are used. There are many things that require bonding materials with different thermal expansion factors and it is not that difficult to manage.

The company I worked for made products that required bonding quartz to plastic. Quartz has essentially zero thermal expansion and the plastics (polypropylene or PVDF) are quite high. The application was for chemical process tanks that could run up to 190C. These bonding surfaces could be 30 or more inches in length so a very significant difference in terms of how much the plastic grew in comparison to the quartz. It took a while to determine the correct adhesion method but it proved to be reliable.

The difference you would see between carbon fiber and aluminum or steel would be very minor under normal temperature variations and could easily be managed with the right epoxy or other adhesive.

Back in the mid 90s I had a Cadex carbon tubed frame with bonded aluminium lugs. I rode it pretty hard for a decade and there were no problems with the bonded joints. I eventually sold it to a work colleague and it was still going strong.

In the early 2000s I also had a Cannondale mtb with carbon chain stays bonded to an aluminium frame. Again no issues with the joint.

It really comes down to the quality of manufacture rather than the mixed materials. Bonding carbon to metal is fine when done properly.

You know what they say about opinions. The IF XS is a fly bike.

The owner of the bike shop I frequent has a Trek\Lemond Tete de Course that is Ti and Carbon, absolutely stunning bike. Has to be 20 years old and he still rides it here and there. Seat Tube, Top Tube, and seat stay are carbon,

Those "spine" bikes were interesting.

Yea they were, and the welds on that thing are so clean, remind me of the welds on high end modern day aluminum frames from Trek\Spec and such. I think they use laser welding if I recall which had only been around for a few years at that point.

Agree the Ti / Carbon and Ti / Carbon / AL bikes were very nice.
A few that come to mind were the serotta ottrott and guerciotti g55 g35.
I have a g35 and it rides wonderful and still looks close to mint for a bike circa 2010
Those Guerciotti models are Columbus aluminum Airplane tubing for the main triangle,
Forks and rear triangle are Columbus muscle carbon fiber woven with a titanium mesh.