Among the hundreds of parts that make up the modern bicycle, the wheelset is unique: it’s the only component that touches both the frame and the road at the same time. That means every aspect of the road surface–good and bad–is transmitted to the frame and rider through the wheels. The same is true in reverse. Every rider command, intentional or otherwise, ultimately meets the road surface via the wheels. In other words, success, failure, performance, and experience depend directly on the design, material composition, and quality of your wheels. We test and re-test in two unforgiving venues: the lab, and international competition. We’ve excerpted the following information from a series of technical discussions prepared by Reynolds design engineers.
Wheel Performance
Three factors define wheel performance:
1) mass/ inertia, 2) mechanical efficiency, and 3) aerodynamic drag. While the mass value of most components, such as the frame, bars and forks, is static, the dynamic nature of a wheel creates an additional performance aspect known as angular acceleration or inertia.
Inertia
Unlike components such as frames, forks, and handlebars, whose performance is evaluated on a static basis, a wheel is evaluated based on inertia. Low inertia significantly and directly affects the power (watts) required to accelerate the bicycle. The contribution of wheel inertia is significant; it is approximately double the effect of the mass of a static component, such as the frame.
The effect of inertia is continuous because a bicycle is constantly accelerating and decelerating. Acceleration and deceleration are continuous through every rotation of the pedal stroke, so wheel inertia is always a significant factor in bicycle performance. In a comparison test the lowest weight wheel typically results in the lowest inertia.
When a bicycle moves in a straight line, the resistance forces retarding motion are balanced by the thrust components developed by the rear wheel. Resistance forces are of five types:
- Aerodynamic forces caused by wind and the bicycle’s motion through the air
- Gravity forces when the road is not level
- Inertial forces experienced when the bicycle is accelerating or decelerating
- Tire rolling resistance forces
- Bearing friction
On level road with no wind, at speeds below 8 mph (13 kph), tire and bearing rolling resistance are the dominant retarding forces. However, the wind resistance increases as the square of bicycle system speed while the rolling resistance increases only slightly with speed, so above 8 mph, the air resistance overshadows rolling resistance. At speeds above 25 mph (40 kph), wind resistance is responsible for over 90% of the total retarding force.
Rim Design
The leading edge of a bicycle wheel shares some common characteristics with the leading edge of an aircraft wing. Because low drag is the goal, not high lift (the higher the lift, the higher the drag), the widest part of the wheel should not be at the leading edge. Low drag airfoil design typically places the thickest portion of the airfoil at about 1/3 of the distance from the leading edge to the trailing edge. Tire selection plays an important role in achieving an airfoil shape that closely adheres to the 33% rule so it is possible to choose a tire that is compatible with the rim for optimal low drag performance. The most common mistake is choosing a tire that is too wide for the rim which will move the widest part of the airfoil shape too far toward the leading edge as opposed to 33% of the chord line.
Tech Update: Vibration Management System (VMS)
Reynolds engineers have employed sophisticated computer modeling of road vibration and layup iterations to create a proprietary layup schedule designed to absorb uncomfortable frequency vibration feedback from the riding surface. At the same time, they’ve managed to balance that damping effect without compromising lateral stiffness, acceleration, feedback, and overall rim strength. According to Reynolds engineer Peter Turner, “the basis for this principle is to capitalize on the anisotropic properties (a material that presents different characteristics when measured in different directions) of carbon fiber material as the optimum choice for building wheels.” That’s a lot of technical language that simply means, Reynolds VMS results in wheels that produce faster response with each power stroke, quicker acceleration, greater lateral stiffness and control, and a more comfortable, less fatiguing ride with each passing mile.
Tech Update: Ultralight technology
For 2009, Reynolds announces a significant technological advancement. Now all DV and MV wheels are designed and built using Reynolds high modulus carbon. This important step means our Ultralight (UL) designation is included exclusively on every DV and MV wheel in our line, both tubular and clincher. The primary benefit of this technology allows us to reduce weight between 5% to 20%, without compromising strength or performance. Dynamic testing shows you can accelerate faster and use less energy when your wheels are lighter. Less energy to keep your wheels spinning means more energy in reserve to make the crucial break, or the winning sprint.
Weight is only half the story. Lab tests show UL technology improves rim temperature performance (the temperature to which a carbon rim in a lab test can rise during simulated braking before it fails) by 17%. The bottom line: Reynolds UL technology helps a rim dissipate heat more efficiently during braking. Just as important, Reynolds UL technology increases the ability for a rim to sustain pre-failure temperatures by a factor of 250%. The bottom line: better braking, better rim durability, better top-end performance.
"Reynolds has mastered the art of manufacturing full-carbon clincher rims that are both strong and light." - Competitive Cyclist
Tubular cross sections
| Clincher cross sections
