Alto Composite Manufacturing

The Alto R-Symmetric hub is an eye catching piece—it has naturally become the focal point of the brand—and we love it! However, as important as hub geometry is to ride quality, a wheel is only as good as the sum of its parts. We’re often asked, “why not just sell the hubs?” Since the answer wouldn’t fit in 140 characters, we wanted to give you a real response.

To begin our discussion of Alto carbon rims, let’s first talk about what carbon fiber is – a composite. A composite structure is anything made up of two or more individual materials (constituents) that come together to make a single material that better suits your application. Concrete is probably the best example, made up of cement and stone to create a material with incredible compressive strength. In the case of a bicycle rim, the constituents are carbon fibers and polymer resin. The great thing about composites is that you can combine those constituents in many different ways to construct a material that is perfect for your application!

The first task in creating your perfect composite material is to find exactly what loading scenario the finished product will undergo during use. In our case, that meant knowing the lacing pattern, bracing angles, and tension of the spokes, as well as the force applied by the ground as an athlete rides/corners/sprints. Once those forces are known, it’s then possible to set about creating the perfect laminate. “Laminate” is just a fancy word that describes the size and orientation of each carbon layer, or ply, that makes up the total thickness of the composite.

There are four main types of carbon fiber weaves (described as the ply’s “tow”):  12k, 3k, 1k, and unidirectional (UD).  An important thing to note about carbon fibers is that they only resist force in the direction of that fiber.  Woven plies (12k, 3k, 1k) have long been used in the cycling industry due to the increased durability and impact strength, but half of the fibers are always pointing in the wrong direction and providing nothing in terms of stiffness, which is certainly not ideal!  Improvements in polymer resin and molding techniques have allowed for increased usage of UD fibers, allowing engineers to customize a laminate structure to ensure that every fiber is working in the intended direction.

You will have noticed two terms in the last paragraph, strength and stiffness, which are often confused when speaking of carbon fibers and “modulus.”  First, modulus describes a material’s stiffness, not its strength.  There is a good metaphor that is usually taught to engineers to help describe these two terms—think of a rubber band and a wooden pencil.  A rubber band will bend, flex, and deform with breaking, and it is very easy to enact these changes in shape.  A wooden pencil, on the other hand, is very rigid and difficult to deform, but it is not very strong and will catastrophically fail with a small amount of force.  The rubber band has very high strength and low modulus, while the pencil has very low strength and high modulus.

The difficulty is designing a composite is that carbon fibers act as either the pencil or the rubber band, but not both. Strength and modulus are inversely proportional - as one goes up, the other goes down. So a carbon fiber product that is “high modulus” is typically used only as a marketing term. A well designed composite uses a combination of high modulus and high strength plies, in specific areas, to account for the forces that that particular area will encounter.

The next step in the manufacturing process comes down to molding, where there are many, many options. But for our purposes we will mention the two main techniques used in the cycling industry – bladder molding and expanded polystyrene (EPS) core molding. Curing techniques seek to achieve many things, but the main goal is to apply even pressure on the inner walls of the composite structure while it cures. The more even the pressure distribution, the stronger and more reliable the final product will be. Bladder molding is a common technique where plastic bags are inserted into the mold and inflated during the curing process. You can probably see the issue with this technique, as the bag typically doesn’t rest perfectly along the inner surface and creates voids/wrinkles that will inevitably cause the part to fail. EPS molding uses a solid foam mandrel, along with painted silicone, in order to apply even pressure throughout the inside of a complicated design. This means the engineer can use less carbon overlap without fear of internal defects that could cause failure. Basically, the inner surface is as smooth and perfect as the outer surface. You can look inside your rim or frame and easily notice the difference for yourself - if you find wrinkles, it was likely molded with plastic bladders.

With all of that being said, what does it say about Alto rims? We utilize high modulus UD carbon fiber plies with orientation specific to our hub’s wide spoke bracing angles. In fact, we change that ply orientation depending on rim depth, since the bracing angle increases significantly for deeper rims. You will find 1k and 3k tows on the brake track and rim bed of our clincher and tubular models, woven with higher strength fibers for added durability. This tow and fiber choice, along with a proprietary heat resistant resin, is why our braking will always be smooth and why you can trust our carbon clincher models in any terrain! Finally, take a flashlight and peer inside of one of our rims. Our EPS molding technique gives you the confidence in knowing that the rim isn’t just as light and stiff as it can possibly be, but also that it is free of internal defects and won’t fail while you are flying down a mountain pass. Safety is paramount!

The best part about being a wheel brand with real design and engineering is that we can continually scrutinize every aspect of our products. Some of those innovations will be ground breaking patents, while others will include existing technology, but you can be sure that every aspect was designed with the purpose of being truly great—to help you achieve the same result.

Bobby Sweeting
Bobby Sweeting