Carbon Fiber


Successfully used in aerospace, motor sports and other applications for years, carbon fiber is also considered the ultimate material for high-performance bicycles. With an incredibly high strength-to-weight ratio, the material is an engineer’s dream. It’s lighter than aluminum and stronger than steel, and a properly constructed carbon fiber frame can achieve an incredible ride quality with the stiffness and agility that performance-minded riders desire.

When Felt introduced its first carbon fiber frame, it was after exhaustive research on material grades and manufacturing techniques. Even though plenty of bike manufacturers were starting to use it, Felt engineers wanted to be absolutely certain that every carbon fiber bike it produced lived up to the company’s high standards of performance and durability.

Grading Carbon Fiber
Raw carbon fiber is made with extremely thin, strong fibers. These fibers come in many different grades—or in engineering terms, “modulus”—based on the material’s strength and stiffness. The higher the grade, the more it costs.

Higher grades of carbon fiber have a higher tensile modulus and are therefore stiffer. This is a good thing. However, high-grade carbon fiber can also be trickier to work with because of the need to maintain a balance between stiffness, strength and durability. It’s that balance that Felt always strives for. A frame that’s simply lighter, or stiffer, isn’t necessarily better. The goal is to balance all of the elements that make a bike perform best when it hits the road or trail.  

In addition to being a challenge to optimize, higher-grade carbon fiber is also more expensive. For these reasons, many bicycle manufacturers steer clear of the material. But Felt believes the investment is worthwhile. Starting with the best materials available is essential to achieving the ride quality that our engineers, and our professional athletes, demand.

Making The Frames
There are many ways to use carbon fiber in bicycle manufacturing. At one end of the spectrum is an age-old method called lug-and-tube. This is the way steel-tube frames have been built for more than a century. With this method, carbon fiber tubes are bonded to lugs, which can be made from aluminum, titanium or carbon fiber. The tubes are inserted into the lugs and the joint is glued together.

The lug-and-tube technique typically results in an overlap of extra material and therefore results in a frame that’s heavier than necessary. Lug-and-tube construction also produces a distinctly “flatter” ride feel because it utilizes so many individual parts and overbuilt intersections.

At the opposite extreme is the technique used by Felt: modular monocoque construction. We start with sheets of unidirectional fiber (picture long, straight, black hair). These sheets, or plies, can be made from fibers with different levels of modulus (60T, 40T and 30T), depending on the specific intended usage of the bike. They can also be mixed and matched. For instance, is the bike aimed at competitive racers who favor light weight and pure performance over anything else? Or is it a sprinter’s bike, built for someone who prefers additional stiffness at the cost of a few grams?

In addition, these unique plies can also be precisely located in the frame to take maximum advantage of their specific properties. For example, stiffer fiber plies may be used in areas of peak stress such as the bottom bracket shell and down tube while higher-strength fiber plies are used in areas particularly susceptible to impact.

Once the perfect blend of materials is established through prototype testing and team feedback the final lay-up is documented and ready for production. During production, the sheets of carbon fiber are already “pre-impregnated” with an epoxy resin, and then plies are cut to the shapes needed to construct the frame. These plies are strategically laid onto specially shaped urethane mandrels. Once the lay-up is complete, it is placed into a symmetrically split CNC-machined mold (think waffle iron). An internal bladder is inserted, and the mold halves are closed and locked. The bladder is then inflated, pushing the carbon fiber firmly against the mold with a precise amount of pressure and heat.

When the heating process is complete, the mold is opened up and the cured frame is removed. Any remaining urethane mandrels or internal bladder material is then removed. The result, effectively, is a perfect frame every time. Because each frame size must have its own molds, monocoque construction is considerably more complicated and expensive than other methods. But the ride quality and unparalleled strength makes it worthwhile. A Felt modular monocoque frame has a lively, responsive feel that’s unequaled by any other bike in the world.

Of course, materials and manufacturing aren’t everything. Prior to all of this, Felt engineers have already spend countless hours in front of their CAD workstations calculating exactly how loads are applied to a bicycle frame to determine the best shape and size of the tubes and intersection areas.


Felt Carbon Fiber Grades
Felt currently uses three types of its own design-specific blends of carbon fiber: UHC-Nano, UHM and HM.

Simply put, Felt’s UHC-Nano is the absolute finest blend of frame material in the world. Because of a cutting-edge construction technique and Nano resin system, UHC-Nano frames maximize the amount of Ultra High Modulus material that can be used. The secret is this proprietary resin matrix. With most carbon bicycle frames, standard epoxy resin is used as a binder to hold the individual fibers together in their desired locations and orientations. But Felt’s Nano Tech is anything but standard. It actually enhances the performance of the frame at the molecular level of the resin with a stronger bond between the individual fibers.

This system results in improved impact strength, but it also enhances the performance characteristics of the bike. How? By giving Felt engineers more options. With improved strength and impact resistance, they can use more of the Ultra High material to add stiffness without the frame becoming too fragile. The thinner walls, improved stiffness and snappy ride quality are all results of the Nano Tech resin.

With this material, we could have chosen to shave a few more grams off the UHC-Nano frames, but with the bikes already so light that our pro team mechanics sometimes have to add weight just to meet the UCI’s minimum competition weight, we instead increased the impact strength and stiffness. So our stiffest and lightest frame is now that much more durable.

Ultra High Modulus (UHM)
The raw fibers used in Felt’s Ultra High Modulus frames allow Felt engineers to meet their stringent requirements for rigidity and strength with less material than the High Modulus frames. The highly refined threads of UHM typically have a higher fiber to resin ratio, which results in a lightweight, lively frame that’s perfect for competitive riders and racers.

Similar to the way metallic frames gain ride quality and liveliness with thinner tube walls, the UHM fibers allows our designers to use incredibly thin-walled tubing. The end result? UHM frames are 20% lighter while remaining just as stiff and strong.

Working with UHM fibers does present certain engineering challenges. For instance, a fiber with more stiffness and strength is also more brittle. Though capable of sustaining massive loads, these fibers are less tolerant of tight-radius bends in the manufacturing process. So thoughtful design is critical. Felt engineers are careful to include as few tight bends as possible, which not only prevents the fibers from fracturing during manufacturing but also guarantees that the material yields the lightest possible frame.

High Modulus (HM)
Felt’s High Modulus clearly illustrates why carbon fiber is ideal for performance bicycle frames. Consider the facts: It’s eight times stronger than 3/2.5 titanium, more than three times stiffer than 6061 aluminum and less than one-fourth the density of steel. Moreover, it can be formed into a wide variety of shapes and exhibits nearly infinite fatigue life.

HM frames have that signature Felt feel with unmatched durability. It’s perfect for riders who want a performance bike that’s strong enough to lasts for years. Even the least expensive carbon fiber road bike in Felt’s 2010 line, the F5 SL, uses premium grade high-modulus fibers for its sleek frame and all-carbon fork. The materials used in this entry-level carbon road racer are on par with many manufacturers’ top-of-the-line models.

There’s a reason the F5 SL’s frame technology is so evolved. Just a few years ago, the same technology was used for Felt’s F1 frameset. So today’s F5 SL incorporates all the advantages of a bike that, not too long ago, was our flagship pro road race model. Because of Felt’s commitment to advancing its carbon fiber technology, you can experience a level of performance previously unheard of at this price.

What does it all mean?
It means that when you choose a Felt carbon fiber product, you can ride it with the confidence, trust and ultimate satisfaction you would expect from a world-class product. It has been researched, tested and re-tested long before you ever ride it, and it has been developed with the help of some of the world’s top professional racers. It means you will experience unmatched engineering superiority and performance for the ride of your life.