INNOVATION THROUGH EXPERIENCE
PERFORMANCE WITHOUT BARRIERS
Throughout the development process of our wheels, lead engineer, Kevin Quan, works closely with his alma mater, the University of Toronto’s Institute of Aerospace Studies (UTIAS). Working with Dr. Phil Lavoie, Associate Professor with a PhD in Aerodynamics, and a number of graduate students the team rigorously tests and analyzes our wheel designs, utilizing no less than three wind-diverse wind tunnels, placing Knight squarely at the forefront of aerodynamic research.
What is ‘Aerodynamics’?
Aerodynamics refers to the interaction between airflow and a moving object, in our case a wheel, and in broader terms the entire bicycle system. The goal for the engineering team at Knight Wheels is to develop a product that not only performs aerodynamically well on its own, but, more importantly, reduces the aerodynamic drag of the entire bicycle system. Regardless of riding conditions – headwind, tailwind, crosswind, ascending or descending – airflow is a major force that all riders face. When designing a wheel to cheat the wind there are three types of airflow that our engineering team need to consider – laminar, turbulent and stalled.
Laminar flow is the most desirable. In a laminar flow situation, the air moves across the system with no disruption or turbulence. This requires numerous rounds of designing, testing, evaluating, reworking, and retesting. Turbulent flow is less desirable. This results in the air moving across the system encountering some areas of friction. This results in dirty air, but does not reach stalled air status.
Stalled air flow is the least desirable. In a stalled air situation, the air separates from the wheel or bicycle system and leaves pockets of spiralling air in its wake. This then further leads to air flowing in reverse direction that leads to high drag and impedes movement.Laminar flow across the wheel, and entire bicycle system, is the ultimate goal but can be incredibly difficult to achieve. By spending a significant amount of time in the design and testing phase, our engineers are able to develop shapes that offer the largest aerodynamic benefit for not only the wheel, but for the bicycle system as a whole.
Why aerodynamics are important to a rider? As mentioned earlier, regardless of riding conditions, airflow is the major force that a rider needs to overcome. Historical research has shown that 80% – 90% of the aerodynamic drag a rider faces is the caused by the rider itself. This essentially leaves 10% – 20% of the aerodynamic drag that the bicycle system is able to impact. While the wheels are not the largest piece of the system (that falls to the frame), they are the first and last elements to interact with the airflow. Add to that fact that the wheels, unlike most other elements, are constantly moving, results in wheel design having a significant impact on the overall system.
Knight Wheels are designed to provide a significant aerodynamic advantage by interacting with the frame and the other elements of the total system. This results in rider needing to produce less watts to ride at the same speed.
University of Toronto
Reinventing the wheel 101
The engineering team at Knight Composites has extensive knowledge of aerodynamics, carbon fiber and an incredibly broad experience in the cycling industry – designing award winning frames, forks and bars in the past. During the research, design and manufacturing process our engineering team leaned extensively on their knowledge to help develop better wheels for the cycling community. In addition to our internal knowledge, we also partnered with best aero minds around.
Throughout the development process for our wheels, our lead engineer, Kevin Quan, worked tightly with his alma mater, the University of Toronto’s Institute of Aerospace Studies (UTIAS). Through this connection, we were able to partner Dr. Phil Lavoie, Associate Professor with a PhD’s in Aerodynamics, as well as a number of graduate students.
Our engineers, along with the researchers at the institute and Dr. Lavoie, began the design process with computer models using Computational Fluid Dynamics (CFD) to develop the initial shapes. From there, we utilized a rapid prototyping process to test the designs in a small format wind tunnel in the UTIAS labs. This allowed us to manipulate the rims on a micro scale – perfecting even the minutest details of our shapes.
Partnering with an educational institution is an uncommon practice in the cycling industry, and added time to the design and development process. That said, at Knight Composites we are confident that by taking this step we are able to offer our customers the best wheels on the market.
What tools does Knight use to enhance the aerodynamic benefits?
During the design process, the engineering team at Knight Wheels utilizes several tools to ensure our wheels are optimized to reduce aerodynamic drag. A number of these tools are utilized by other aerodynamic focused companies, while others are not. Adding in a few additional steps to the design process does lengthen the overall development time, but we believe the aero savings realized are worth the additional production time.
Computational Fluid Dynamics (CFD)
The design process for each of our wheels begins with highly trained engineers sitting in front of incredibly high-powered computer using Computational Fluid Dynamics (CFD) software. CFD software simultaneously measures a near-infinite number of algorithms that helps our team determine what the best wheel shape is based on our targeted results. Sample CFD w streamlinesThe engineers are able to design a shape, test its aerodynamic properties and compare those properties with other shapes that have been designed and tested. Given that the average number of shapes our engineering team go through for each wheel is in the hundreds, CFD significantly reduces the initial design phase and is a cost-effective method of determining aerodynamic benefits. While CFD does offer significant time and cost savings, it does have its challenges as well – which is why our design process does not stop there. The biggest challenge is that, as finely tuned as CFD is, airflow does not always act as the model predicts. This means a wheel shape may not offer the same level of aerodynamic benefit under real world conditions as our engineering team expects during the CFD design process. Once the engineers have short-listed the best performing shapes, we move our design process to the windtunnel to validate CFD results under more real world conditions.
Before our engineering team can begin testing in the wind tunnel, they must first fabricate the shapes that were designed in CFD, this is done using Rapid Prototyping (RP). RP allows the engineering team to manufacture each of the shapes to the exact measurements designed in CFD using a 3D printing process. The RP shapes are then taken into the tunnel and the aerodynamic properties of each are further tested. Low speed wind tunnels (LSWT) have been used in bicycle design for many years. They are used to test everything from bike frame design, to water bottle placement, to rim shape. LSWT allow the engineering team to continue the design process by testing the aerodynamic properties in near real world conditions.
Small Wind Tunnel Testing
Wheel in Tunnel FarOnce CFD design is done, most manufacturers move into a large format wind tunnel to continue development and testing. Before Knight Wheels moves into a large format tunnel, however, we first take cross-sections of the wheels into a small format wind tunnel. Determining the aerodynamic properties of a wheel is an exact measurement – the slightest variation can lead to vastly different results. A smaller format wind tunnel moves less air through a smaller space and has fewer variables leading to more accurate testing. While this does add time to the prototyping phase, it provides our engineering team with more accurate testing that leads to a better finished product.
Large Wind Tunnel Testing
After the Knight Wheels engineering team have further refined the wheel shape in the small format wind tunnel, design and development is moved into a large format tunnel. During this stage, our engineers further measure wheel performance and refine the shapes as the aerodynamic properties are optimized for real world conditions. In addition to testing our own wheels, the large format wind tunnel allows our engineers to compare the performance to other wheels available in the marketplace. [/accordions]
Our design process begins with computer models using Computational Fluid Dynamics (CFD) to develop the initial shapes. We then utilize a rapid prototyping process to test the designs in a small-format wind tunnel in the UTIAS labs. This allows us to manipulate the rims on a micro scale—perfecting even the most miniscule details of our shapes.
Our Design Philosophy
Our wheels are conceived and designed for maximum rider benefit. That goes beyond just speed – our wheels are fast, of course, but we look for balanced performance.
Trailing Edge Aerodynamic Manipulation
TEAM technology focuses on the trailing (rear) edge of the rim. Specifically, we address how the trailing edge affects air flow from the rim to the tire, and onto the down tube and the rest of the frame. TEAM shaping is designed to maximize the airflow attachment around the down tube, the rear triangle, and ultimately the entire bike. The majority of aero wheels currently available place the design focus on the leading edge—the outer edge of the tire and rim. At first glance, this seems to make sense, as research has proven the frontal area has a significant impact on overall aero performance. The aerodynamics of the leading edge of the wheel is largely dependent on the tire, and while this data should not be ignored, our engineers discovered that designing around the trailing edge could offer a far greater aerodynamic benefit. Starting with a NACA airfoil-based shape, the engineers reworked it by manipulating the arc and elongating the shape. The resulting rim is a proprietary shape that:
- Eliminates flaws in more common “V” and “U” shaped frames
- Offers a gradual widening of airflow around the trailing edge, producing less disturbance over the down tube and frame
- Provides the optimal curve in rim for best air trajectory around the tire-down tube interface
- Minimizes “wind steer” by moving a higher percentage of lift to the back of the wheel
Since first being introduced to the market, carbon wheel braking has been a major concern with consumers. Despite the numerous advancements that have been made over the years, the thought of poor braking performance is still a significant reason many people will not make the switch to full-carbon wheels. The challenge with the braking system on a carbon rim is a result of the carbon material itself. When the brakes are applied, the caliber is closed, and the brake pads press against the rim to slow it down. The pad rubbing along the rim creates friction, and that friction creates heat – under extreme braking conditions, a significant amount of heat can be produced. If this potential heat is not considered during the design phase, the adhesives that hold the carbon fiber together can breakdown. The result is the rim begins to separate along the braking track until the eventual point of failure. To address this concern, our engineering team took the approach to overbuild our carbon structure at the brake track. Most carbon rims on the market have a wall thickness of 1.5mm at the brake track; Knight Wheels are designed with 3mm of thickness. While this thicker section of carbon adds a bit of weight to the rim, it also adds significant heat-resistance as well. Under braking load, the heat has more carbon material in which to dissipate, allowing temperatures to stay cooler, and the adhesives to stay strong. Manufacturing a wheel that is aerodynamically superior is the goal of Knight Wheels, however, safety is also a key concern. Each of our rims must meet our rigorous standards, which we believe surpass those of the cycling industry. Case in point, some of our competitors’ wheels repeatedly failed our testing protocol at 1/3 of our standards. While these self-imposed requirements add some weight to the rims, and increase our design time, it also ensures the safety of each rider that puts their trust in Knight Wheels.
We are the only rim manufacturer implementing an Expanded Polystyrene (EPS) layup and molding process to produce our rims. This cutting edge process combined with aerospace-grade Toray carbon fiber—the same material used in Boeing’s 777 aircraft—allows us to produce a lighter, stronger, more reliable and more precisely constructed rim than any other manufacturer.
EPS Molding Process
Expanded Polystyrene (EPS) layup and molding is the standard for creating frames and forks for the best race bikes in the world. At Knight, we use this same process to create our products.
Most carbon fiber rims look smooth and seamless on the outside, but what’s inside is equally as important. Making a carbon fiber rim involves compressing layers of carbon weave and epoxy resin into a mold to get the desired shape. Traditionally, inflatable bladders are used inside the rim to force the material into the mold, but because the shape of a bladder can’t be finely controlled there can sometimes be wrinkles or inconsistent thickness in the finished rim. These irregularities can lead to delamination or premature stress fractures — every fold, every wrinkle a potential point of failure.
By utilizing an EPS Molding System, we get internal surfaces as smooth and wrinkle-free as the exterior. This increases strength due to the uniformity of the fibers, pushing it into exactly the desired shape with consistent thickness and no wrinkles. The result is a lighter, stiffer and more consistent final product.
We can make EPS forms to the exact shape that we want before laminating carbon fiber around them and placing the whole system in a mold. When heated, the individual beads in the EPS forms swell. Out in the open they’d reach 40 times their original size, but constrained by the mold they exert pressure on the inside of the carbon fiber, pushing it into exactly the desired shape with consistent thickness and no wrinkles.
As the sole rim manufacturer implementing this cutting edge technique within our manufacturing process, combined with our aerospace-grade Toray carbon fiber, used in Boeing’s 777 aircraft and many others; Knight Wheels can offer a lighter weight, stronger, more reliable and precisely constructed rim.
Military grade carbon
Not all carbon fibers are created equal, and we choose Toray of Japan’s Torayca® brand fibers. Toray Industries is the unequivocal global leader in the carbon fiber industry, and as such is the world’s number one supplier of carbon fibers for aerospace applications, including Boeing’s 787 Dreamliner and the Airbus A350; Lockheed Martin’s F-35 Lightning II fighter jet, the International Space Station, satellites and rocket casings.