Road Cycling - carbon seatstays / seatpost

i'm getting mixed comments from different lbs (and even different employees at the same shop!!!) about the pros/cons of carbon in the rear triangle - what will be the differences, if any, between say a full aluminum bike with a carbon fork & seatpost and another aluminum bike with a carbon fork and carbon seatstays?

from what i understand, the carbon and alum are about equally as strong and the carbon is a touch lighter and will absorb a bit more of the road buzz. will the full alum bike be stiffer through the bottom bracket -- is this even the right spot on the bike to make the comparison or is it at the dropouts where the wheel is spinning...

hopefully you 'experts' will be able to set me straight so i can decide on the bike. thanks in advance.

matt

Sorry I am not an expert but I whent from a steel bike to an AL/Carbon as you describe above and the new bike is very much stiffer and so far I have no complaints about harshness after about 600 miles. I never rode an all AL bike however, so I don't know what that is like.

Listen carbon is comfort, Carbon is light, Carbon is strong...hell its the $hit diamonds are made of....do I need to say more.

Listen carbon is comfort, Carbon is light, Carbon is strong...hell its the $hit diamonds are made of....do I need to say more.
pencil 'lead' is the s$it diamonds are made of to :D

pencil 'lead' is the s$it diamonds are made of to :D

As is the stuff in my grill. :D

That said, I am however a big fan of well made carbon frames and components. ;)

I test rode carbon/alu bikes before going with steel. Instead of trying to get you to go for steel (Orbea Ultrafoco Carbon, just in case) I'll try to answer based on my comparing my Cannondale CAAD3 full alu vs. the carbon/alu bikes I rode.

In summary, the carbon takes the harshness off of aluminum while keeping the BB stiffness and quickness that alu is typically known for. You still get the lively feeling that only a metal can give (no dig to you carbon folks, but I just prefer metal to carbon in terms of road feel). But you get that with a pretty smooth rear end.

The flip side is that alu frame builders have gotten pretty damned good at what they do and are making frames with shaped and butted tubesets that take a lot of the discomfort found on older alu bikes out without throwing in another material.

It all depends on the frames in question. Is it a CAAD 7 Cannondale full alloy vs. ?? or ?? There are alot of variables.

About carbon rear stays:
Most carbon rear stays are a "generic" part that a manufacturer like Kinesis makes. This part is then glued into a aluminum stub, thus making the "wishbone" rear carbon seatstay.
Although the actual stays maybe lighter than aluminum (maybe not) the entire rear stay assembly usually makes the frame heavier than a full aluminum frame of equal caliber.

As for vibration dampening, the actual carbon material doesn't carry the vibrations the same way as metal. Does that make it more or less comfortable? Again, depends on which frames you are comparing.

As for stiffness in the bottom bracket, the key there is the downtube, chainstays and torsion on the seattube. The seatstays have little to do with that kind of stress.

In both your examples, the aluminum structure is going to be stiff and carbon stays won't be a major factor in bb flex.

As RacerX said, it all depends on the frames. If you look at Guru v.s. Cannondale for example, (Guru with the carbon rear triangle and Cannondale with the all aluminum optimo stays) you can see that each company has thier own theory on what makes the "best" rear triangle/frame/fork.

Guru boasts a more comfortable ride due to the carbon rear triangle. What they fail to mention, is that the carbon has to be butted into the aluminum. The two frame materials overlap and are glued together, adding more weight. Also, much like the reinforcement in an all carbon steerer, extra care is taken, so that when the aluminum is glued to the carbon, the carbon seatstay bridge doesn't get crunched. The beefy seatstay bridge actually takes away from the carbon triangles plush ride. The bridge sort of kills the dampening effect to some degree.

Cannondale's all aluminum frame has a reputation to be a harsh ride. However, the people at C'dale have utilized the hourglass-bend seatstays to combat this stiffness. With the long, thin stays on the Cannondale, without the carbon/alumium butting, the all aluminum ride is much lighter, and still quite comfortable.

In my opinion.. Either go all Aluminum, or Full carbon. When you start combining the frame materials, you add weight, sort of a marketing ploy for old guys with a lot of money.

Then again, it's all up you what you find more comfortable/practical and what your willing to pay for.

Rubber side down :-)