Carbon costs more than aluminum. But there are manufactures who make high quality alloy frames which costs just as much, if not more slightly than mediocre carbon frames.In your opinion, which is better, stiffer, and lighter?If you need examples....umm like Cervelo\'s S1 or CAAD9 compared to the lower quality carbon frames.Personally I would go with the high quality Aluminum because it would be stiffer, but not nesaccarily lighter. A mediocre carbon frame are known to not take stress well and can break more easily than a high quality Aluminum. I would only go with Carbon if it was high quality.A high end aluminum frame would be a better choice than a mediocre carbon frame. Aluminum frames are light, and a good one could well be lighter than a lower end carbon frame. Stiffness is an overrated quality in a frame. A frame that is unrelentingly stiff can beat you up and be a chore to ride. Good frames are stiff where they need to be and compliant in the right places to make them comfortable to ride. Cannondale was one of the first companies to start building quality aluminum frames for road bikes, before any of the other major bike companies on the market today, and they continue to sell high end aluminum bikes today. Early aluminum frames had durability issues, but those problems have been resolved. Frame weight is not much of an issue. Keep in mind that the rest of the components of a bike weigh far more than the frame. You can\'t turn a 25 pound bike into a 15 pound bike with a better frame, the difference in weight between a top level carbon fiber frame and an aluminum frame will be much less than 1 pound, even a good steel frame will weigh less than 2 pounds more than the lightest carbon frames.You are only talking about a difference of ounces between a high quality aluminum frame and a mediocre carbon frame. The difference is that you will be buying a new carbon bike in a few years when it cracks and wears out. Most of the weight of a bicycle is the components, anyway. A steel framed bike with well chosen components can be as light or lighter than a carbon framed bike with poorly chosen components. Keep in mind that carbon fiber bicycles are built for racing, and hardcore dedicated racers don\'t use the same bike for years at a time. The top racers don\'t even use the same bike for a year. I don\'t know about you, but i don\'t have a sweet sponsorship deal, so I have to buy my own bikes, and when I do buy a bike, i expect it to last a long time. Since the weight difference between a high end aluminum bike and a carbon fiber bike is pretty miniscule, factor time and cost over time in to your equation. Is a weight savings of one pound worth having to buy a new bike every three to five years instead of every ten years or more? An aluminum bike will easily last twice to three times as long as the carbon bike, so when you are doing your math, double or triple the cost of the carbon bike to see what riding on carbon will cost you over time.A combo of both is nice. But if I had the choice, I would go stiffer frame (aluminum) with carbon stays. For a carbon frame, the carbon has to be decent quality, not like the carbon that is used for making Raleigh frames. Low quality!I am not sure where some of these posts came from, but from someone like myself who road cycles 6000 to 8000 miles per year and has a 3 year old carbon fiber frame, I have never had any problems with my frame... I have never heard of any carbon bike breaking unless it was in some MAJOR crash... the same crash that would destroy almost any bike (except cromealloy steel)... That being said, carbon frames are usually the lightest out there, but they can be pricey. Yes, they can be stiffer, but that is a GOOD thing because the power transfer through the drivetrain is better, especially when you have to get up out of the saddle. While riding regularly, especially on the flats, it gives a bit, providing a plush ride. I love my Specialized Roubaix Pro, pretty much everything on the bike is carbon, from the FSA cranks to the Specialized carbon stem... But be prepared to spend at least 3000 bucks to get the bike with good components. Ride safe and have fun!Other related question