carbon seatstays + aluminum frame

since carbon usually gives more comfortable rides, will this affect acceleration if the carbon part is only on the seatstay (as in hardtail compare to full suspension in mtb)?

for example this frame on the specialized allez:

I'd doubt it. It would be more dependant on frame geometry and the engine. The carbon doesn't flex like suspension on a mtb, it only tends to dampen bumps a bit and on this bike it's hard to say if they aren't just carbon wrapped aluminum stays anyways.

That's a full carbon stay. I have the same setup on a Klein Q Pro Carbon, great acceleration. Maybe theortically the AL is stiffer, but I can sprint just as good in a full CF Giant TCR. If there is a difference 99% of the riders would never be able to tell.

It's a gimmick creating unnecessary extra joints. Al can make good frames. Composite frames can be good. Neither type has any real vertical compliance in the rear triangle. There's little point mixing the two. Full aluminium or monocoque composite is to be preferred.
Having said that, it is unlikely to cause you any problems. Just don't believe the composite "no-bump" hype.

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I disagree. You need to provide some argument for this.

There are extra joints necessary b/n Alu and CF components.

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I thought I did. Let me make it clear that I don't think that bikes built this way are necessarily bad, it's more like carbon fibre brake levers, CF rear derailleur parts, or, dare I say it, CF chainsets - carbon fibre used not because it is the best material for the job but because it shifts stock. CF levers,RDs and chainsets are not worse than alloy, they are just unnecessarily expensive.
CF frames or stays do not reduce bumps - a rear triangle does not realistically deflect in the vertical plane regardless of material - so an Al frame is not improved by the addition of a composite rear triangle. What you are introducing is unnecessary extra bonding points in the frame, allowing for a hypothetically higher failure rate. In reality, many manufacturers do this a lot and so I imagine that they are quite good at making it safe. It still doesn't make it worthwhile, except for marketing.

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The bike company that sponsors my team provides us with two models; full AL and a compiste rear triangle. The AL frame is actually lighter because the lugs require more material. Both frames ride awesome. I've got a C'dale that rides like a dream, though people claim AL gives too harsh a ride. Ride what you feel comfy on.

This true. Bill Holland....maker of Holland frames....said he tested various types of rear triangle configurations and found in every case the seatpost deflected much more than the rear triangle for a given "bump."

Also, it is wrong to assume that CF offers better ride quality. Ride quality is a function of design, construction, QC, and fit to some degree, but ride quality is much more dependent on tire inflation pressure and the bike's contact points with the biped riding it. Ride quality cannot be defined by a material.

AMEN!!!! I've easily done 5 plus hours on a Cannondale CAAD8, the dreaded harsh ride of aluminum, with no issues whatsoever. I have also loved riding and racing my carbon Giant TCRs this past season. I attribute that more to the compact geometry than the frame material.

I picked up a CAAD8 frame a few months ago to race crits on. 1,500+ miles later I'm still waiting for the so-called harshness to kick in. I've tried everything, super stiff wheels, tires with 145 psi, Thomson alum seat post, still no harshness. I must be doing something wrong, this frame was supposed to knock my fillings loose....

Yeah, you're definitely doing something wrong. Since that CAAD8 is aluminum, you should have all sorts of stress fractures and other injuries from the tortuously harsh ride that aluminum always delivers. I mean, there's no way your Cannondale can have a sweet ride, certainly not a magic carpet ride like every steel bike delivers. Actually, I'm surprised your bike has lasted this long. I mean, that aluminum should have failed from fatigue just a few days after you first rode it.

Aluminum even tries to warn you with it's cheap price tag too... Boy do I feel cheated.
Next time I'll spend 4 times as much on carbon...

Good thinking, especially since CF doesn't vibrate.

I agree but disagree. I owned a 2006 lemond etape, all aluminum, very comfterble, kinda fast, now i own a 2007 specialized tarmac expert, all carbon, not as comftorble, but VERY fast. I do think comfort has to do with design and construction, but also material, the carbon doesn't wiggle, so to speak, as much as aluminum does.

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