Upper Wheel Fairings Reinvent the Bicycle Wheel
Upper Wheel Fairings Reinvent the Bicycle Wheel
Upper Wheel Fairings reinvent the bicycle wheel to minimize overall vehicle drag, increasing headwind penetration speeds.
Upper Wheel Fairings reinvent the bicycle wheel to minimize overall vehicle drag, increasing headwind penetration speeds. Read more
About this project
Upper Wheel Fairings for Road Bikes
With your help, we will soon introduce revolutionary wheel drag-reduction technology to the bicycle world with our first wheel-fairing product. Shielding a bicycles’ faster-moving upper wheel surfaces from headwinds yields dramatic increases in speed without sacrificing crosswind stability. And these gains in pedaling efficiency actually increase in the presence of headwinds.
One can readily feel the difference in penetrating even a slight headwind. Test our Upper Wheel Fairings for yourself, and you will never again want to ride without them. Please help us introduce this new invention, by becoming one of the very first to enjoy our drag-reducing Upper Wheel Fairings on your road bicycle.
Our Brief Story
Upper Wheel Fairings shield critical drag-inducing surfaces on a bicycle from headwinds, significantly boosting performance. With our Upper Wheel Fairings installed, cyclists report dramatic gains in speed while penetrating headwinds. One can readily feel the difference, as headwinds really slow a bicycle having exposed upper wheel surfaces. Depending on headwind conditions, riders have achieved speed gains ranging between three to over 20 percent. And the relative gains only tend to increase in rising headwinds. See our website for the latest test reports.
Unshielded upper wheel surfaces augment critical drag on wheeled vehicles. In fact, most vehicles with unshielded upper wheels are needlessly aerodynamically handicapped. Our Upper Wheel Fairings restore a bicycle to a more optimal, minimal-drag configuration.
While wheel fairings generally are not allowed under traditional race rules, the recreational or commuting cyclist need not adhere to the drag-inducing restrictions of the race community. The cycling public should enjoy the inherent drag-reduction that comes from shielding the upper wheels from headwinds. However, we have found that the bicycle industry has little interest in promoting this potentially disruptive innovation, since for decades their focus has been mainly for the benefit of racers.
Your contribution will not only help facilitate our first production run, but should our campaign goal be reached quickly, it may also help garner more general media attention. We need your support. Please contribute, and cycle smarter with Null Winds Technology.
About the Product
Our first product is a kit of Upper Wheel Fairings adaptable for installation on most traditional-framed road-style bicycles. There are an estimated 1.5 million road bikes sold in the United States each year, with a greater number sold in Europe, not to mention the rest of the world. And the total number of road bikes already in use is likely mTuch greater. Our product should be suitable for most of that market.
Fairings are made of aircraft aluminum, providing the best combination of stiffness and weight. Total weight added to the bicycle is just over two pounds. The additional weight increases the combined weight of the bicycle and average rider by just over one percent. Any slight loss in speed while climbing steeper hills as a result of this slight increase in weight is more than offset by the increased wind penetration speeds achieved both on the downhill segments and on the flats whenever headwinds are present.
Each fairing is gently curved by a stiffener bar fastened to the inside surface, such that the fairing can be positioned flat adjacent to the wheel rim. After powder-coat paint is applied, nylon spacers are attached along the inside surface of the fairing to protect the wheel rims from incidental contact with the fairing during heavy vibration or side-wind gusts.
Initial installation normally requires several hours to complete by first-time installers. The procedure requires installing mounting clamps and mount bars to the fork and rear stay assemblies, arranging the fairings on the bicycle, locating two holes to be drilled in each fairing, and aligning the fairing to the wheel assembly. Once the mount hardware is secured to the frame, the fairing can be easily removed from the bicycle and replaced to the same position in seconds, facilitating the removal of the wheel when necessary.
For those unfamiliar with bicycle repair, we recommend using an experienced bike mechanic for the initial installation. Your local dealer should be able to help. Before installing, please review both the installation manual and also the video presentation for installation tips. The installation manual includes detailed instructions on measuring the fork and rear stay diameters (using a piece of string), needed for specifying clamp sizes. These measurements must be taken for each particular bicycle before placing an order.
We are confident that our product will eventually find widespread use in the cycling world, simply because it works. Our Upper Wheel Fairings represent perhaps the single-most effective drag-reducing modification that can be made to the common road bicycle. Surprisingly, the reason is actually quite simple.
About the Technology
Consider the wind speeds on the surfaces of a moving wheel as shown in the wind profile diagram: under null headwind conditions, the wind is null at the bottom where the wheel is in firm contact with the stationary ground; and near the top the wind rises to twice the vehicle speed. By shielding the upper surfaces, the effective wind on the wheel is greatly reduced. And if a headwind is also present, the wind is reduced significantly more.
And since the power needed to overcome drag rises in proportion to the cube of the wind speed, shielding the upper wheel surfaces — thereby reducing the effective speeds of impinging winds — yields dramatic gains in propulsive efficiency. And from examining the wind-profile diagram, it becomes clear that these gains increase rapidly in rising headwinds. Propulsive efficiency actually increases in stronger headwinds. Recent on-bike road tests confirm this dramatic trend.
Imagine my excitement when I first confirmed the potential performance gains on my first ride with a crude prototype of the fairings. I found it hard to imagine that no one had examined this effective approach to drag-reduction. After talking to a few racers, I quickly began to understand why they often immediately dismiss the idea. They know that their UCI race rules prohibit the use of fairings. Often, they don’t even want to try them. Racers must face a very painful drag-inducing restriction. It is a shame they must fan the wind with their wheels, effectively slowing them down.
This longstanding, drag-inducing practice should be limited to the racing world. The general public need not endure the painful extra effort that racers feel while cycling against a headwind. Instead, we want all to discover the performance benefit provided by shielding the upper wheel surfaces of recreational and commuting bicycles.
About the History
Recent efforts of the bicycle industry to reduce drag have been largely directed toward the development of very expensive aerodynamic wheels, which are often made of carbon fiber. Wheel rims have become deeper, heavier, and with fewer spokes, all with increasing expense. Our Upper Wheel Fairings are generally more effective — and economical — than these expensive aero wheels, since wheel drag is actually concentrated only on the uppermost wheel surfaces. Even so, bicycles using these expensive aero wheels will also become faster with our Upper Wheel Fairings installed.
This claim may seem a bit hard to believe. At first, I also had trouble comprehending the significance of this innovation. So please let me share a little history of my discovery.
As an engineer, I was already aware of the wind profile across a vehicle wheel: where the wind is null at the ground level and up to twice the vehicle speed at the top. Since the ground is not moving, there can be no wind at the bottom of the wheel. Where there is no wind, there can be no drag. This point is often overlooked.
And the upper section of the wheel moves forward against the oncoming headwind, thereby magnifying the effective wind speeds. At first, this insight can seem a bit confusing since the wheel itself moves at the vehicle speed. In fact, we have noticed incorrect diagrams of this wind profile sometimes published in the engineering literature. So the true wind profile across the moving wheel is the first thing to keep in mind.
The second point to understand is the relative drag sensitivities of various wheel surfaces. Since I was once a paraglider pilot in southern California, I was also keenly aware how significant drag can be on the thin lines used on a paraglider wing. In fact, in the early days of the sport, I used to spend long hours modifying my own glider with extra-thin cascaded lines in order to fly faster.
Spokes are like thin lines, with relatively high drag sensitivities. However, spokes above the axle of a wheel are moving forward must faster than the vehicle, which dramatically increases drag and the power needed to propel the vehicle. So it seemed logical that these upper wheel surfaces needed to be shielded from headwinds. I began to wonder why I did not see upper wheel fairings on bicycles. When I started searching for prior art on the internet, I was quite surprised that I could not find anything. So right then I decided that if no one else was going to investigate this concept, I would.
I quickly fashioned some crude fairings to my 35 year-old heavy road bike. Since I had not ridden a bike in many years, I was shocked the first time I managed to test my old bike fitted with crude prototypes of upper wheel fairings. I simply could not understand just how I was now able to ride the same old heavy bike — configured with crude upper wheel fairings — in at least one gear higher than when I was more than 35 years younger. My bike weighed more than 25 lbs and had high, 36 spoke-count wheels. Though I did not fully understand the reasons, I knew at that moment that I had discovered something significant.
My next step was to purchase a modern low spoke-count carbon-frame bike. After testing both bikes on the same six-mile loop, I found that my old heavy bike with the fairings was just as fast as the new modern bike without fairings. The difference over the 22-minute loop was just a couple of seconds. Imagine my excitement, as I knew right then that I had likely discovered something fundamental about the wheel.
From that point, it was simply a long effort to conduct further tests and understand the mechanics of this innovation. I designed a crude fixture to test a bicycle wheel driven by an electric motor on the top of my truck, functioning as a poor-man’s wind tunnel. A friend — a retired aerospace physicist — joined my effort in the Lancaster desert to help record data over a wide range of wind speeds, up to 55 mph. We measured definite reductions in drag on the wheel, but not enough to explain the speed gains that we were measuring during on-the-bike road tests. This was a bit puzzling.
As a mechanical engineer, I decided to reexamine the published literature for the mechanical models commonly used to model drag on a bicycle wheel, and quickly found a problem. The engineering community seemed to misunderstand precisely what was happening when a wheel is used on vehicle. Past studies claimed measured gains using wheel fairings were marginal at best. However, the proof that these conclusions were incorrect was in the data from our own bicycle road tests.
It did not take long to understand the correct mechanical model for drag on a vehicle wheel, which forms the basis for an extensive patent application, which is now pending. After considerable effort to prepare and file the patent application, we remain confident that the application will prove successful. High-speed vehicle wheels have been around for nearly 100 years without this simple innovation. It is time that the drag-reducing benefits from using our Upper Wheel Fairings are introduced to the world.
We introduced early prototypes for the first time at our booth during last year’s Sea Otter Classic 2013 bike festival near Monterrey, California. While riding our demonstration bikes both with and without fairings, a number of riders experienced dramatic reductions in drag. We received only positive comments from riders. Nearly everyone wanted to know when our product would be available. At Sea Otter, we even met an inventor of the mountain bike, who came to our booth to offer his congratulations for this innovation.
Also at Sea Otter, a professional rider from Road2Recovery who was also concerned about rider safety for his veteran riders, reported enhanced stability in the presence of crosswinds. While he noticed crosswind forces on his body, he reported sensing no corresponding sideways increases on the bicycle, and found this puzzling. While enhanced stability was not our primary goal in the development of this innovation, it is readily explainable: Upper Wheel Fairings actually enhance the effective traction of a vehicle. Any potential crosswind forces caused by the addition of our Upper Wheel Fairings is largely offset by the enhanced tire traction. Bicycles fitted with our fairings are often more stable in gusty wind conditions.
Since last spring, we have refined the early prototypes into a smaller production design that can be fitted to most traditional road bikes. The proper drag model indicates that in most cases, the smaller design is actually more efficient than the early prototypes. We have been using this design to conduct a number of precision road tests, in order to confirm the performance gains.
As mentioned, the measured gains are dramatic. Racers tell us that a five percent increase in speed is a huge increase for a bicycle. And most tests have greatly exceeded five percent. Most racers find our claims are hard to believe. For this reason, we have used the latest precision power meters, which also measure headwinds, to record our data outside under real-world road conditions. Detailed test reports are available on our website. And many more tests are planned this spring and summer.
One of our first independent tests was indoors at a Velodrome near Los Angeles last fall. For various technical reasons regarding the instrumentation that was used, the reported data was inconsistent and unrepeatable. However, the test rider — a top-level Category-1 racer — reported that the faired bike definitely felt faster under null wind conditions. When asked, he indicated that he definitely preferred the faired bike to the unfaired version. While disappointed that we did not get good data, I knew that the drag model predicts only minimal gains under null wind conditions anyway.
One of the first independent tests conducted outside in strong headwinds was by former road racer living in France, who is now a venture capitalist focused on the bicycle industry. He had contacted me last fall, and I sent him the first early set of fairings. After hurriedly installing the fairings himself over the weekend on his own bike, he reported gains of “two or three” miles an hour the next day. And late last year, an active road racer testing in a strong headwind near Lancaster, CA was excited to experience similarly dramatic gains.
So far we have installed our fairings on the regular commuting bikes of a number of veteran cyclists. All have reported immediate increases in speed when facing headwinds. The first local commuter to try the fairings was a bike mechanic, who reported shaving nearly 10 minutes off his 45-minute commute into headwinds toward his job in Santa Monica. Another veteran rider also reported setting a personal best on his second commute to work. Still another extreme distance racer put over 800 miles on his bike in January, without having to adjust the initial installation of the fairings at all. He also reported having changed a tire once without needing to remove the fairings.
All these reports have been encouraging. However, the proof is in the test data. We have now obtained confirming data in sufficient quantity to be certain that the gains are readily achievable.
Please visit our website for detailed test reports, and a more detailed discussion about this technology. As the patent application still remains unpublished for now, we must restrict releasing further details about the correct drag model until later in 2014. However, I look forward to discussing this technology in greater depth at that time, including the reasons why upper wheel drag forces are actually further magnified against propulsive counter-forces.
About the Future
In the future, our drag-reduction technology will have implications beyond the world of cycling. Automobiles and trucks with exposed upper wheels are needlessly inefficient. Have you ever wondered why jeep vehicles are particularly bad gas-guzzlers? Their exposed tires have aggressive tread patterns oriented directly against the wind at the worst location, near the top of the tire. This drag-inducing effect is exacerbated at highway speeds, wasting fuel that could be easily saved by extending the front fenders forward to shield the upper wheels.
And while we are not familiar with the complex rules of automotive racing, we must conclude from knowing the correct drag model that many modern race cars are designed with inefficient front wings, likely augmenting total vehicle drag unnecessarily.
And large trucks with many more wind-exposed tires have a similar problem. Although improving truck efficiencies is a recent area of intense research, it is clear to us that wheel fairing technology in use today is overly extensive — inducing too much drag — thereby offsetting much of the intended benefit.
Thus, we expect our drag-reducing technology will eventually contribute to the worldwide efforts to improve fuel efficiencies in automobiles. Hence, our innovative Upper Wheel Fairings can be considered green technology, helping to reduce fuel consumption for the benefit our environment. Even if you do not own a road bicycle, we hope you will consider contributing to our success, and help enable us to eventually convince the automotive industry to improve the aerodynamics of many fuel-inefficient vehicles.
About the Campaign
Our production prototype is quite close to the final mechanical configuration. A few minor details must be checked before bringing the product to market. However, this process is expected to go smoothly during our active Kickstarter campaign.
One remaining issue is to check the fit of the fairings for a variety of caliper brakes. We also need to confirm that the current design can indeed accommodate a wide range of bike frame sizes. We have sources for the various parts, as well as for the manufacturing of the fairings and mount bars, together with paint and labeling. We need to finalize the installation manual and installation video, complete packaging labeling, and organize warehousing for product shipping and distribution.
No doubt there remains considerable work ahead. Still, the innate simplicity of the final product reduces our risk for putting together the organization needed for the deliver our rewards. Most of the work is scaleable, and easily out-sourced to a variety of local machine and paint shops. We already have in place a professional accounting software package needed to handle inventory and customer data. An e-commerce software package is also available which directly integrates with our current accounting software. As order volumes increase, we need only train a bookkeeper and assemblers to deliver rewards to our backers, and provide customer service.
Marketing and sales is another area that requires serious attention. Until recently, we had not launched any advertising or promotion, other than placing our booth at Sea Otter last year to announce this innovation. Garth Magee attended the Interbike Industry Conference last September in Las Vegas, where he happened to meet the inventor of popular low spoke-count aerodynamic wheels. He in turn introduced Magee to the president of a major manufacturer of perhaps the most popular aerodynamic rims used by many racers today. So with these contacts made in our short time exposed to the bicycle industry, it is clear that some of the major bike companies are becoming aware of this innovation. Still, few have yet to fully comprehend the significance of this technology.
We have refrained from premature promotion, until we were certain that our data firmly supports our claims, and that we had mapped a clear path to producing our first product. We are now ready for our launch, and are beginning to advertise. Still, we need your support.
Overcoming incorrect assumptions about the drag mechanics of the vehicle wheel is a daunting challenge. Leading bicycle companies have a long history developing aerodynamic technology specifically geared for the race community. Decades of marketing from the bicycle industry has largely convinced the cycling public that dramatic advances are simply not possible.
Please help us overcome this entrenched view by contributing to our campaign and spreading the word about this innovation. Reaching our campaign goal will provide the funds needed to order the wide variety of clamps, economically manufacture the other parts, rent needed warehouse space, hire staff, advertise and demonstrate future market potential for our product.
We are confident that we now have the capability to ship a limited number of early rewards by early summer. If we exceed our goal, a larger number of rewards should be shipped in late summer. And if we greatly exceed our goal, it may be early fall before we are properly organized to ship the larger volumes. While the ultimate reward volume from this campaign is hard to predict, we hope to ship all rewards by fall. In any case, we are committed to shipping all rewards (each priced at a substantial discount over retail) before introducing our product to the general market.
Please contribute to our campaign, and spread the word through Facebook and other social media. Help us change the bicycle world for the better. By contributing, you will also help enable us to eventually bring needed fuel savings to the automotive world. Help us introduce this green technology into both the bicycle and the automotive industries. Our drag-reducing technology can make bicycles a more popular means of transportation, and can also contribute to improving fuel economies of many automobiles and trucks, thereby improving the environmental health of our planet.
Fairings are installed in a series of steps:
- Clamps are adjusted and fitted to the front forks and rear stays of the frame.
- Mount bars are attached to clamps, and positioned proper distance from the axle.
- Fairing stay bars are positioned and secured to the lower clamps.
- Clamp retaining stays are secured to the front upper clamps, preventing clamps from sliding down highly tapered forks.
- Fairings are positioned level on both sides of the wheel, adjacent to the wheel rim, and loosely secured using the fairing stay clamps and locknuts. Fairing stays are secured into position by tightening the lower clamp locknuts. The locations of two thru-holes to be drilled in each fairing are located under the mount bars and marked on each fairing.
- Fairings are removed and the two marked holes are drilled in each fairing.
- Fairings are installed and positioned adjacent to the rim with sufficient clearance to minimize rubbing against the rim, while providing adequate wind shielding of wheel surfaces.
The fairings can be mounted to most traditional-framed (metal or carbon), road bikes having caliper rim brakes (using standard pads without tire guides) if the following minimum clearances exist:
- On the front, a minimum clearance space of at least 3.8 cm exists between the inner surfaces of the forks. The clearance should be confirmed to exist along the entire length of the fork between the axle and near the inner rim of the wheel (up to 29 cm measured from the axle). See Figure 1 for this measurement.
- At a distance of 29 cm measured from the axle along the length of the fork, the circumference of the fork at this location does not exceed 6-3/8 inches (16.2 cm). See Figure 2 (a string is used to measure the circumference at this location).
- At a distance of 19.5 cm measured from the axle along the length of the fork, a minimum of 5.0 cm of clearance space exists between the inner surfaces of the fork assembly. See Figure 3.
- At a distance of 29 cm measured from the axle along the length of the fork, the total width measured between the outermost surfaces of the fork at this location should not exceed 3.375 inches (8.6 cm).
- Bicycle rims should be 700c in size.
- Tires should not exceed 32 mm in width (700x32c).
- Caliper brake pads that include narrow tire guide ears may need to be replaced with standard pads without tire guide ears.
While we have not yet found a road bike not conforming to these clearance requirements, some carbon forks may have particularly narrow inside clearances for the wheel, making installation of fairings somewhat more challenging. For those situations, please measure your bike carefully to ensure adequate clearance.
Risks and challenges
With any endeavor there will exist some level of risk. Our challenge is to minimize our chances for failure through strategies such as:
• Minimizing the mechanical complexity and variety of the product
• Minimizing the organizational complexity of the business
• Establishing relationships with key parts suppliers
• Establishing scaleable production roadmap using local vendors
• Campaign rewards limited to incremental production roadmap
• Validating dramatic performance gains through road-tests
• Confirmed market potential through receptive public interactions at our booth at the recent Seattle Bike Expo, March 2014
My own 20 years experience as the administrative partner in a small fund development consulting business, together with my nearly 15 years as a design engineer in the aerospace industry, has given me the confidence that managing the initial growth of this new endeavor is within my capabilities. I am in good health with a solid economic footing. I am also reducing my partner responsibilities in my consulting business in order to focus full time on this new endeavor. I am excited to bring this new innovation to the cycling world, and hope that you will support our growth.
Still, it is likely that some problems will occur from time to time. We intend to inform contributors of any delays or unexpected issues that might affect delivery schedules. Our contributors are our friends. They will be the first to experience our product, and will help us spread the word about this exciting innovation. Until every reward is delivered to our friends, this will always be our focus. Our business cannot succeed without this core value receiving our foremost consideration every day. Thank you for your support!Learn about accountability on Kickstarter
This is one of the first questions frequently asked by riders. And the answer to us was at first surprising, until we began to fully understand the drag mechanics. Shielding the upper wheels enhances traction, largely offsetting any increased side wind force susceptibility.
Racers have commented that using the fairings seems no more sensitive to crosswinds than when using their traditional race wheels. The likely reason is that the fairing surface area is somewhat balanced on the front wheel about the fork turning axis (which lies slightly behind the axle), reducing turning forces from sidewinds. Fairing area is concentrated near the top of the wheel only, where it affects the moment about the vertical turning axis far less that if it were located toward the front and rear of the wheel, as are deep-rim race wheels.
Deep race rims tend to provide an unbalanced moment about the turning axis, with their large areas concentrated also forward and rearward from the axle. This location more easily imparts a moment about the turning axis from sidewind forces, since the rim surface area forward of the axle is located further from the turning axis than the corresponding rear rim surface area. This imparts an unbalanced torque from side winds on the front wheel, destabilizing the cyclist.
In fact, a pro rider from Road2Recovery was surprised to find that larger prototype fairings felt more stable than his triathlon race bike. He stated that for some reason he did not feel the crosswind forces on the bike, but felt the winds on his body, and asked how he might get the fairings installed on his own race bike.
The production fairings are substantially smaller than the early prototypes, reducing side wind effects even further. We conclude that the remaining crosswind effects are largely offset by the enhanced traction, yielding better stability in sudden gusts in many cases. I myself was once blown sideways 2 feet by a sudden gust while downhill testing at Sea Otter at 30 mph. Without the fairings, I fear I would have been down.
Moreover, the use of the upper wheel fairings are more effective at reducing drag than deep race rims. Thus, more traditional narrow rims with higher spoke counts can be used in combination with the fairings, reducing sidewind sensitivity even further.
Still, the fairings are not magic in crosswinds. Any bicycle will be subject to crosswind forces. However, the enhanced traction should provide greater opportunity to retain control during sudden gusts.
Update 4-24-14: Just completed some road tests with a RAAM veteran (who regularly rides 200 miles) in very gusty conditions, with crosswinds gusting well over 20 mph. He commented that the bike with fairings felt no more unstable in these conditions than the unfaired bike. We discussed the pivot axis unbalanced torque issue, and he remarked that this was the first time he has heard of this analysis (he is also an engineer). He also stated that almost no one would ride in these conditions anyway.
The gaps between the fairings and the wheel rim is on average set to about 1/8-1/4 inch or so near the front of the fairing, and can be allowed to expand toward the top and rear of the fairing. However, the gap is not that critical, since the object is to shield the vast majority of the wind from entering the wheel area beneath the fairing. Slight leakage wind beneath the fairing slows considerably as it passes through the gap and expands to fill the larger volume between the spokes.
Power is saved in proportion to the cube of the effective wind speed on the spokes, so the effect is dramatic even with imperfect shielding. Saved power is equivalent to increases in speed. With the fairings installed, penetrating the wind feels quite unusual on a bike, since our experience tells us we should slow dramatically in any headwind. Instead, we seem to slice through the wind in an unnatural manner. The effect is often startling, at first.
It turns out that wheel drag is a far greater component of the total bicycle drag than is commonly assumed by the industry. And the vast majority of this wheel drag is concentrated on the uppermost surfaces. This is why installing the fairings can be so effective.
Yes, forwardly-extending fenders with fairings has been undergoing testing. Early results are mixed when using the smooth road tires of road bikes. While we expect additional gains for mountain bike tires, we have focused thus far only on road bikes.
The problem we have noticed with previous attempts to integrate wheel fairings for aerodynamic benefit is the size of the fairings often used. If the fairing sizes are too extensive, the additional frictional drag from the extended surface area tends to offset the gains from shielding only the critical drag-inducing surfaces.
The insight needed is to recognize the extreme sensitivity to vehicle drag of the uppermost wheel surfaces over all other vehicle surfaces. And spokes have drag coefficients one to two orders of magnitude greater than smooth fairing surfaces. Spokes need to be shielded.
Deep rims have greatly extended surfaces areas as compared to spokes. While the drag coefficients of their smooth surfaces are much smaller than for spokes, their comparatively large surfaces areas tend to provide similar overall drag. As such, deep rims can suffer a similar problem in terms of vehicle drag, since the extended surfaces are moving against the same high effective wind speeds. The moving surfaces of the deep rims also should be shielded in order to minimize overall vehicle drag.
Every high-speed vehicle needs to have a portion of the upper wheel surfaces shielded from headwinds. The drag model provides a basis for determining the extent of the needed shielding, which depends on vehicle configuration and operating conditions.
Isn’t the front wheel the primary source of wheel drag, since the rear wheel resides in air disturbed by frame components?
Early test results indicate not much difference between the front and back wheel. Perhaps profile shielding by the bike and rider shift about ten percent of the drag to the front wheel, but the difference measured thus far has been too small to determine with any conclusiveness.
Bicycles are operated in a relatively slow wind speed regime, so that most parts of the frame and wheels (except for spokes near the top of the wheel) experience largely laminar flow of air around them. Thus, air flows around the tire and rim smoothly, filling into the space in which the spokes are revolving. Thus, shielding of the rear spokes by the frame parts and rider is likely minimal. And wheel fairings on the rear wheel are therefore also highly effective.
Some have suggested that they did not notice much difference when using a handlebar fairing. This would be likely, since the fairing is attached to the frame where the wind is far slower than on the upper wheel surfaces. Recall that the power dissipated is proportional to the cube of the wind speed. So since the wheel surfaces of the upper wheel suffer far higher wind speeds than on any other part of the vehicle, it is only logical that shielding frame components with other frame components is not likely to produce as much drag reduction as when shielding the faster moving upper wheels.
Furthermore, the large surface area of the handlebar fairing which directly opposes headwinds is likely to produce a large pressure drag, while the streamlined minimal surface area wheel fairing produce little to no pressure drag, and only minor frictional drag.
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