Spoke Fins Reduce Bicycle Wheel Drag, Even in Crosswinds

spoke fins banner spoke fins front wheel

Spoke Fins cut critical spoke drag by up to 67%, even in crosswinds. Streamlined Spoke Fins swivel like a wind vane in response to variable crosswinds, which constantly change orientation as the wheel rotates. Made of tough nylon plastic, Spoke Fins are designed to fit most bicycle wheels employing standard 14 gauge round spokes. The streamlined tailfin snaps easily onto each spoke by hand, converting the round spoke into an equivalent bladed spoke which is effective not only in headwinds, but also in crosswinds.


Spoke Fins are available in four different colors: natural white, maroon red, Safety Green (neon), and black.


Neon safety green Spoke Fins enhance rider visibility at night.

Spoke Fins Converts the Round Spoke into Bladed Spoke — Effective in Crosswinds:

  • Optimally Streamlined Tailfin Swivels about Standard Round Spoke
  • Eliminates up to 67% of Spoke Drag in All Winds (Drag reduced 3X)
  • Far More Effective than the Bladed Spoke in Windy Conditions
  • Increases Cycling Speed and Stability — Even in Crosswinds
  • Enhances Wheel Visibility for Greater Cycling Safety
  • Clips onto Standard 14-Gauge (2.0 mm) Spokes

Optimally streamlined Spoke Fins reduce the spoke drag coefficient by up to 67% in the critical faster-moving drag-inducing region located nearest the wheel rim. Since the round spoke has a relatively high drag coefficient — thereby becoming the major contributor to overall wheel drag — reducing critical spoke drag also reduces total wheel drag. Spoke Fins taper lengthwise to reduce drag principally on the critical uppermost spokes, where wheel drag most retards vehicle propulsion.

spoke fin detail
3D-printed Spoke Fins: Confirmed substantial drag reduction.

As the wheel rotates, Spoke Fins automatically adjust their streamlined alignment for the changing orientation of the effective wind vector on the spoke. Spoke Fins swivel to reduce pedaling effort under any wind condition, becoming especially effective on typical recreational bicycles with higher spoke-counts. And by adjusting to changing crosswinds, Spoke Fins increase the aerodynamic transparency of the wheel and thereby increase rider stability.


 

One can readily feel the difference. Try our Spoke Fins for yourself, or give them to a friend or family member. Be one of the first to enjoy our innovative Spoke Fins on your bicycle.

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About the Product

Bicycle racers know that bladed aero-spokes quickly become ineffective in crosswinds. Spoke drag rapidly increases when winds are directed crosswise across the flat blades. In a direct headwind, the common round spoke develops much more wind drag than does a bladed spoke. However, against a crosswind the bladed spoke can actually produce much more drag than the round spoke.

spoke fin detail
Spoke Fins are narrowly tapered, limited to about the width of standard 14 gauge spokes

When competing outdoors, bicycle racers often choose round spokes over bladed aero-spokes, since significant crosswinds are present during as much as 85% of the ride, especially in windy conditions. Thus, a cyclist normally faces a direct headwind relatively infrequently. Instead, there often exists some crosswind component of the wind on the wheel, often negating the low drag benefit of bladed spoke.

spoke fins bike
Spoke Fins increase the aerodynamic transparency of the wheel, reducing drag and increasing stability.

Attaching the streamlined tailfin to the round spoke reduces the spoke drag coefficient from a relatively high 0.4 (maps to 0.82 for the typical spoke Reynolds number) compared to a substantially lower 0.13 (maps to 0.26 for the typical spoke Reynolds number) — as measured from Fluid Dynamic Drag, Hoerner, 1965, page 13-19, figure 50 — a three-fold reduction in drag. Since the fin is positioned in the critical drag-inducing region near the wheel rim, Spoke Fins can easily decrease overall spoke drag by more than 50%. And since Spoke Fins swivel about the spoke in response to crosswinds, they are effective in all wind conditions - rather than when only facing a direct headwind.

Drag coefficients chart
Tailfin drag coefficients compared to that of a Round Spoke (= 0.4)

Clipping this simple device onto each spoke provides a surprising reduction in upper wheel drag. And upper wheel drag is the most critical drag force retarding vehicle propulsion, especially in headwinds.


3D-printed Spoke Fin

As demonstrated by of our upper wheel fairings, reducing spoke drag in the critical upper wheel region can dramatically reduce overall vehicle drag, especially at faster speeds and when facing headwinds. Our fairings have been extensively road tested and shown to produce typical speed gains from 10 to 20% when facing moderate to stronger headwinds.


Upper Wheel Fairings: Road testing demonstrates dramatic speed gains achieved facing headwinds through reducing critical upper wheel spoke drag.

Spoke Fins produce similar drag reduction at faster speeds. Spoke Fins were recently tested by Manuel Quiros — a veteran racer who has set four UCI one-hour velodrome records during his career, as well as a three-time participant of the prestigious RUSA-Paris Brest Paris endurance cycling event. Quiros has confirmed substantial drag reduction at speeds above 15 mph, where speed gains quickly increase since as speed increases drag becomes the predominate force opposing vehicle propulsion. Quiros reports that the gains also become readily apparent whenever facing an external headwind. He also reports remarkable stability in crosswinds.

quote-spoke-fins-manuel2
 

After several hundred miles of testing while commuting around Los Angeles, Quiros states that his bike is both faster and simply feels much more stable. And Quiros also reports that his own bike has become not only faster, but is actually more enjoyable to ride. On his first longer sustained ride (a night ride under low winds) with Spoke Fins installed on standard 32-count wheels, Quiros averaged a fast 22 mph over 45 minutes.


Optimized for injection molding with detachable streamlined retaining clamp, which keeps fin from sliding down the spoke.

Recall just how quickly a moderate headwind slows a bicycle? Surprisingly, the exposed upper wheel surfaces cause much of this dramatic slowing, since drag forces on these fast-moving surfaces is magnified by leveraging (by nearly a factor of two) against propulsive counter-forces applied at the axle. Moreover, leveraging greatly magnifies the propulsive power simply needed to overcome upper wheel drag.

Spoke Fins reduce drag on bicycles in both headwinds and crosswinds without the need for costly investment in expensive carbon wheel sets. In fact, the effectiveness of deeper rimmed carbon wheels is surprisingly limited due to the much larger exposed surface area in the critical drag-inducing upper wheel region of these wheels. The extensive upper surfaces of deeper rims induce even more drag that can largely negate any benefit from reduced drag obtained by using shorter spokes on these deeper rims.

Since the publication of our pending patent application in mid-2014 — which noted the extreme upper wheel sensitivity on overall vehicle drag — leaders in the the wheel building industry have begun shifting from traditional deeper aero rims back to shallower lightweight rims with much less exposed surface areas. And top racers have already begun using the shallower rims in major races during the 2015 season.

Instead of deep rimmed aero wheels with major exposed surfaces areas, using the thin minimal area Spoke Fins on longer spokes together with traditional shallow rimmed wheels having minimal critical upper wheel surface areas yields the optimum configuration for enhanced wheel drag reduction. This improved configuration combines spokes that are streamlined for crosswinds using minimal exposed surfaces with shallow rims yielding optimal aerodynamic wheels also having reduced total weight.

Spoke Fins are available in a variety of colors. Each fin also includes an optional retaining clamp, which snaps onto the spoke, preventing the fin from sliding down out of position when rotated toward the top of wheel.

About the Technology

As demonstrated by our upper wheel fairings — another recent invention — reducing drag on a bicycle's faster-moving upper wheel surfaces yields dramatic increases in speed whenever penetrating headwinds. The most critical vehicle-drag-inducing wheel surfaces are always located above the axle near the top of the wheel, where wind speeds far exceed the vehicle speed. Below the axle, wind speeds are greatly reduced and actually impart very little drag on the vehicle. As discussed above, the swiveling tailfin streamlines the spoke — in both headwinds and crosswinds — while positioned in this critical upper wheel region.

Since headwinds exacerbate drag on these upper wheel surfaces — which move forwardly against the oncoming headwind much faster than the actual vehicle speed — reducing drag on these critical surfaces is essential to reducing drag on the bicycle. Spoke fins reduce drag on these critical upper wheel surfaces, even when facing significant crosswinds.

Consider the wind profile across a moving wheel: under null headwind conditions, the wind is also null at the bottom where the wheel is in firm contact with the stationary ground; near the top the wind rises to twice the vehicle speed. By reducing drag on the upper wheel surfaces, the effective drag on both the wheel and the vehicle is greatly reduced.

The wind profile diagram also demonstrates that while the headwind component varies with elevation on the wheel — from null speed at the stationary ground to twice the vehicle speed at the top —the crosswind component of the wind must instead be constant with elevation on the wheel. Thus, crosswinds dominate much below the level of the axle where headwinds are greatly diminished.

(Note that the plots of many computational fluid dynamic models incorrectly depict headwinds flowing rapidly near the bottom of the wheel where wheel surfaces are nearly stationary. The lower wheel instead simply displaces most air to the side as it rotates along the ground.)


Note Effect of Reduced Drag on Upper Wheel

Spoke Fins swivel on the spoke in response to crosswinds. As the fin rotates through the critical drag-inducing upper wheel region, the effective headwind component dominates over the crosswind component. The tailfin responds by becoming more aligned with the headwind near the top of the wheel.

As the fin rotates into lower positions, the crosswind component eventually dominates over the reduced headwind component, and the tailfin swivels to be more aligned with the crosswind. In this way, Spoke Fins reduce drag on the spoke throughout the rotation of the wheel.


Spoke Fins swivel, responding to the changing wind vector at various locations around the wheel.

While expensive bladed spokes are often used to reduce wheel drag, they are most effective only under null wind conditions. Crosswinds impinging across the flat bladed portion causes flow separation turbulence behind the spoke, dramatically increasing drag and negating any benefit of the bladed design. In a severe crosswind, the drag coefficient of a flat bladed spoke can quickly increase much beyond that of a round spoke.

Spoke Fins increase the aerodynamic transparency of the wheel. As an example, consider a cyclist traveling forward at 15 mph in a 10 mph crosswind, where the effective wind vector impinging the critical topmost spoke is off-axis from the bicycle centerline by at least 20 degrees. This angle only increases as the spoke rotates into a lower position, and the dominance of the crosswind component increases still further.

A crosswind angle of more than 20 degrees will certainly increase drag on a bladed spoke, quickly becoming even more drag than that on a round spoke. (This can be easily demonstrated by using a flat hand positioned outside the window of a moving car. Experiment with different angles of the hand against the wind to find the increase in drag induced in all but the most streamlined orientation of the hand into the wind.)

Spoke Fins swivel to adjust automatically for the sidewise wind, reducing drag on the round spoke even when facing stronger crosswinds. As a result, in a crosswind the bike becomes not only faster but also more stable. Cyclists report feeling more stable with a more solid connection with the ground, and are often able to ride even hands free in a moderate crosswind.

More information regarding the drag mechanics of a wheel is summarized in our Drag Reduction Flyer, which recently has been well-received both by the professional auto racing community in Indianapolis (Dec., 2014 - PRI Trade show) and by the industrial trucking community in Louisville (March, 2015 - Mid-West Truck show).

About the Invention

Spoke Fins are but one embodiment of a comprehensive pending patent application (now with allowable claims pending issuance). Other embodiments of this invention include upper wheel fairings, an aerodynamic bladed spoke which is also effective in crosswinds, an aerodynamic automotive wheel with oval spokes, and an off-road tire having aerodynamic tire tread pattern.

As described in patent application US2013/070498, upper wheel drag is a far greater source of vehicle drag induced by the wheel than has been previously recognized. Lower wheel surfaces induce very little vehicle drag and can be largely ignored. In fact, the net wheel drag is actually centered very near the top of the wheel. And upper wheel drag is actually magnified through leveraging against propulsive counterforces applied at the axle. Thus, it becomes even more essential to reduce upper wheel drag in order to minimize the needed propulsive counter-forces, especially when facing external headwinds.

Reducing critical upper wheel drag also increasingly reduces the differential power needed overcome increased drag as the vehicle speed increases. Cyclists report that with Spoke Fins installed, the faster they go the more easily it seems to go even faster. This effect is due to the cubic relation of wind speed on drag. Since drag rises with the cube of the wind speed, reducing the drag coefficient of the upper wheel surfaces dramatically reduces the extra power needed to slightly increase speed at higher and higher vehicle speeds.

At higher speeds, it becomes increasingly difficult to increase vehicle speed even an extra mph. As the speed increases, cyclists have the sensation of facing an increasingly stiff wall of wind. This increased resistance is largely produced by the exposed upper wheel surfaces, which move forward against the wind much faster than either the vehicle frame or rider surfaces. And the cubic relation causes drag to increasingly shift to be concentrated more and more on the faster moving upper wheel — as either vehicle speed or external headwinds increase.

By reducing the drag coefficient of the upper wheel, Spoke Fins reduce the extra power needed to increase vehicle speed, reducing the wind wall stiffness sensation. At either higher cycling speeds, or when facing stronger headwinds, Spoke Fins make it easier to increase speed an extra mph for any given vehicle speed or external headwind condition.

spoke fin drag coefficient diagram comparison
Streamlined Spoke Fins Reduce Drag by 3X.

Specifications

Spoke Fins are less than six and one-half inches long and weigh less than 1.5 grams each. A typical full set of 64 fins weighs 95 grams (less than 3-1/2 ounces). The fins are optimized to fit most bicycle wheels employing standard 14 gauge round spokes (2.0 mm or 0.079 inches in diameter) with standard diameter spoke nipples.

Small diameter wheels on kids' bicycles may not have sufficient spoke length to accommodate the fin. And a few wheel rims with very short spokes having acute angles at the nipple connection may inhibit free rotation of the fin. Please measure the free length of the spoke on your bicycle to ensure proper fit.


Spoke Fins are very light and less than 6-1/2 inches long.

Installation

Instructions: Simply position SPOKE FINS along the spoke with the larger end of the fin located nearest the outer wheel rim. Locate the retaining clip on each end of the fin and press by hand until it snaps onto the spoke. The end clips fit loosely around standard 14-gauge round bicycle spokes.

For best performance, spoke surfaces should be cleaned before fin installation. Unpainted spokes can be cleaned using a common green scouring pad. However, in order not to damage the surface finish of colored spokes, use a softer cloth.

The fins are designed to swivel easily about the spoke in light winds, especially after a break-in period of a few miles of cycling in windy conditions. In motion SPOKE FINS slide outward naturally toward the spinning wheel rim.

The optional retaining clamp (attached to the small end) may be installed to keep fins from sliding down the spoke. However, before installing each fin itself, simply press by hand the attached retaining clamp onto the spoke, positioned closer to the wheel hub. To ease installation of the tight-fitting clamp, orient the clamp at an angle where the very end of the clamp is pressed on first. (A jeweler's flat-nose pliers, tire iron or similar tool may also be used.) Then cut the fin from installed clamp, and only then install the fin itself.

Slide the clamp along the spoke to adjust for several millimeters of sliding clearance. Adequate clearance allows the fin to slide along the spoke in response to rough road conditions, minimizing any chance that the spoke slips from between the fin guide legs. To ensure optimal aerodynamic performance, periodically check that the fin guide legs remain properly centered on the spoke.

Made of durable nylon, innovative SPOKE FINS are highly effective and should provide long-lasting performance. The fins can be easily removed and re-installed by hand whenever desired. In the unlikely event that a fin becomes detached from the spoke, please check the fin and re-install before continued cycling.

Neon Safety-Green Spoke Fins
Spoke Fins Installation
Spoke Fins Swivel In CrossWinds; Riding in a Circle
Spoke Fins Swivel In CrossWinds

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