HK40009481B - Airless flexible tire and wheel assembly - Google Patents

Description

Airless flexible tire and wheel assembly

Technical Field

The present invention relates to the field of transportation technology, and more particularly to an airless flexible tire and wheel assembly having a torque-reducing tread pattern.

Background Art

Mobile agricultural irrigation systems, such as center-pivot systems and linear systems, are commonly used to irrigate large fields and typically include a conduit extending across several irrigation jumpers. Each irrigation jumper supports a conduit section elevated on a support tower, which includes a wheel assembly configured to move the conduit across the field along a path along the ground. The wheel assembly can include conventional pneumatic tires or "airless" tires. In embodiments of airless tires, the wheel assembly typically includes a rigid wheel and an airless, flexible tire mounted on the rigid wheel. The rigid wheel has spaced, outwardly projecting spokes to form a polygonal or other non-circular shape. The airless, flexible tire has a rigid section aligned with the outwardly projecting spokes and a flexible section configured to deflect inwardly between the outwardly projecting spokes when the flexible section engages the ground. The airless, flexible tire exerts a higher torque on the ground near the outwardly projecting spokes. However, in certain applications and field conditions, a lower maximum torque or a more evenly distributed torque curve is desirable. Even if the change is permanent, switching wheel assemblies based on the desired maximum torque or torque curve is highly impractical and prohibitively expensive. For this reason, farmers often choose to continue using high-torque wheel assemblies. This results in excessive field wear and fatigue on the drive motor and other moving parts of the irrigation crossover.

Summary of the Invention

The present invention solves the above-referenced and other problems and limitations by providing an improved airless flexible tire for covering the wheels of an irrigation system.

The airless flexible tire can be configured to be mounted on a rigid wheel having a central hub and a plurality of tire supports. The central hub is configured to be attached to the axle of a mobile support tower of an irrigation system. The tire supports can be mounting bosses or other radially extending protrusions, fasteners, or separate components radially attached to the central hub via fasteners or interlocking geometry.

An airless flexible tire generally includes a circular belt, a plurality of drive lugs, and a plurality of traction lugs. The circular belt includes an inner surface, an outer surface, and left and right side walls extending between the inner and outer surfaces. The circular belt may also include reinforcing elements, such as fabric sidebands or endless steel belts, that limit stretching and reinforce the airless flexible tire.

The drive lugs extend radially inward from the inner face of the circular belt and are annularly spaced apart from one another to engage the tire support of the rigid wheel. The drive lugs form a plurality of annularly spaced rigid high-torque points on the airless flexible tire near the tire support of the rigid wheel. A primary objective of the present invention is to reduce the high torque generated at these high-torque points or to equalize the torque generated by the wheel assembly, as explained below. The drive lugs can be integrally formed with the circular belt and can include complementary geometric structures, such as H-shaped ribs, for securing the airless flexible tire to the rigid wheel.

The traction lugs extend radially outward from the outside of the circular belt and are annularly offset from the drive lugs to be positioned between the tire supports of the rigid wheel. The traction lugs and the base portion of the circular belt form a plurality of annularly spaced flexible segments on the airless flexible tire. The flexible segments are configured to deflect radially inward when the traction lugs engage the ground. The traction lugs include a central traction lug and two offset traction lugs. The central traction lug is positioned equidistantly between adjacent drive lugs and includes a distal surface and multiple side surfaces. The distal surfaces are substantially horizontal (i.e., perpendicular to a radial axis extending through the central traction lug) and symmetrical about the radial axis. As the airless flexible tire rolls over the ground, the side surfaces stretch at different angles to maintain traction.

The offset traction lugs are positioned on either side of the central traction lug and are substantially identical. Each offset traction lug includes a distal surface and a plurality of side surfaces. The distal surface tapers at an angle between 1 and 45 degrees from a radial axis extending through the offset traction lug toward the nearest drive lug. As the airless flexible tire rolls over the ground, the side surfaces stretch at different angles to maintain traction. The offset traction lugs may extend at an angle between 1 and 45 degrees from the radial axis toward the nearest drive lug.

In use, as the rigid wheel traverses a path along the ground, the airless flexible tire engages the compliant soil layer. More specifically, as the flexible section deflects into the recesses between the tire supports, the rigid wheel's tire supports push high-torque points into the soil, forming a generally wavy track with alternating peaks and valleys. As the flexible section deflects into these recesses, the central traction lugs grip the peaks of the wavy track, while the offset traction lugs grip the sides of these peaks.

Because the flexible section is curved into a concave or arched shape, each traction lug is urged radially inward depending on its position on the flexible section. For example, because the central traction lug is positioned at the center of the flexible section, it is urged radially inward with little rotation. When rotating at least partially about the nearest high-torque point, the offset traction lug is urged radially inward less than the central traction lug. Due to the angle at which the offset traction lug extends from the flexible section, the offset traction lug becomes substantially upright relative to the ground when rotating about the nearest high-torque point. Simultaneously, due to the angle of the distal end surface relative to the flexible section, the distal end surface of the offset traction lug becomes substantially level with the ground.

Each traction lug has an effective height that is determined by its actual height, the angle at which the traction lug extends relative to the radial axis, the angle of the traction lug's distal surface, and the amount of deflection of the flexible section near the traction lug. For example, the central traction lug may be taller than the offset traction lug, but the flexible section may deflect inward more near the central traction lug than near the offset traction lug. Therefore, even if the actual traction lug heights differ, their effective heights can be substantially equal. Because high torque points do not deflect inward, the traction lugs are also spaced apart from these high torque points. In this way, the traction lugs at least partially equalize the wheel's rolling radius, reducing the torque generated near these high torque points. In one embodiment, when the airless flexible tire moves over the ground, the traction lugs achieve a uniform rolling radius for the wheel, resulting in a consistent depth of the traction lug soil impression. Alternatively, the traction lugs may form a sinusoidal profile or any other suitable profile in the soil.

The airless, flexible tire described above offers several advantages over conventional airless tires. For example, the traction lugs at least partially equalize the rolling radius of the wheel, which reduces the torque generated at high torque points. The traction lugs form a corrugated profile in the soil, which helps prevent erosion. The traction lugs can also form a sinusoidal profile or any other suitable profile, which further limits soil erosion. The traction lugs are spaced apart by at least half the lug width to improve soil loss when the traction lugs are not in contact with the ground. The side surfaces of the traction lugs are drafted to further improve soil loss and increase the contact angle between the traction lugs and the soil.

This summary is provided to introduce in simplified form a series of concepts that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to limit the scope of the claimed subject matter. Other aspects and advantages of the present invention will become apparent from the following detailed description of the embodiments and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the present invention are described in detail below with reference to the accompanying drawings, in which:

1 is a perspective view of an irrigation system on which a wheel assembly including an airless flexible tire constructed in accordance with an embodiment of the present invention may be mounted;

FIG2 is a perspective view of an airless flexible tire constructed in accordance with an embodiment of the present invention;

FIG3 is a side view of the airless flexible tire of FIG2 mounted on a rigid wheel; and

FIG. 4 is a partially enlarged side view of the airless flexible tire of FIG. 2 .

The drawings do not limit the invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention.

DETAILED DESCRIPTION

The following detailed description of the present invention refers to the accompanying drawings that show specific embodiments in which the present invention can be practiced. These embodiments are intended to describe various aspects of the present invention in sufficient detail to enable those skilled in the art to practice the present invention. Other embodiments may be utilized and changes may be made without departing from the scope of the present invention. Therefore, the following detailed description should not be understood in a limiting sense. The scope of the present invention is limited solely by the appended claims, along with the full scope of equivalents to which such claims are entitled.

In this specification, reference to "one embodiment," "an embodiment," or "embodiments" means that the referenced feature or features are included in at least one embodiment of the present technology. Separate references to "one embodiment," "an embodiment," or "embodiments" in this specification do not necessarily refer to the same embodiment, and are not mutually exclusive, unless so stated and/or as would be readily apparent to one skilled in the art from this specification. For example, features, structures, behaviors, etc. described in one embodiment may also be included (but not necessarily included) in other embodiments. Thus, the present technology may include various combinations and/or integrations of the embodiments described herein.

Turning now to the drawings and initially to FIG1 , an exemplary irrigation system 10 is illustrated that includes a plurality of wheel assemblies constructed in accordance with an embodiment of the present invention. The illustrated irrigation system 10 is a center pivot irrigation system that generally includes a fixed center pivot 12 and a main section 14 pivotally connected to the center pivot 12. The irrigation system 10 may also include an extension arm (also commonly referred to as a "swing arm" or "angle arm") pivotally connected to the free end of the main section 14.

The fixed center pivot 12 can be a tower or any other support structure around which the main section 14 can pivot. The center pivot 12 draws water from a well, pond, or other source and can also be connected to a pond or other source of agricultural products to inject fertilizers, pesticides, and/or other chemicals into the water for application during irrigation. The center pivot 12 can supply water to a conduit 16 that carries the water along the length of the main section 14.

The main section 14 can include a plurality of mobile support towers 18A-18D, the outermost of which is referred to herein as an "end tower." The mobile support towers 18A-18D are connected to the fixed center pivot 12 and to each other via truss sections 20A-20D or other supports, thereby forming a plurality of interconnected spans. The irrigation system 10 illustrated in FIG1 includes four mobile support towers 18A-18D; however, the irrigation system can include any number of mobile support towers without departing from the scope of the present invention.

Each mobile support tower can comprise a pair of wheel assemblies 22A to 22D and one or more drive motors 24A to 24D that are installed on the transmission tubes 26A to 26D. The embodiment of wheel assemblies 22A to 22D is described in more detail below. Drive motors 24A to 24D can comprise integrated relays or external relays, so these drive motors can be started, shut down, and reverse. Drive motors 22A to 22D can have some speeds or can be equipped with a plurality of variable speed drives, and can be started, shut down, and reverse.

Each truss section 18A-18D carries or otherwise supports a conduit 16 or other fluid distribution mechanism. A plurality of sprinkler heads, spray guns, drip nozzles, or other fluid ejection devices are spaced along the conduit 16 to apply water and/or other fluids to the ground below the irrigation system.

Irrigation system 10 may also include an optional extension arm pivotally connected to end tower 18D and supported by a pendulum tower having steerable wheels driven by a drive motor. The extension arm may be coupled to the end tower via an articulated pivot joint. The extension arm folds inward relative to the end tower when not irrigating the corner of the field and may pivot outward away from the end tower when irrigating the corner of the field.

The irrigation system 10 may also include one or more high pressure sprayers or end guns 28 mounted to the end tower 18D or to the end of the extension arm. The end guns 28 may be activated at the corners of a field or other designated areas to increase the amount of land that can be irrigated.

It will be understood that the irrigation system 10 is shown and described herein as an exemplary embodiment of the wheel assemblies 22A to 22D described in detail below. Other equally preferred embodiments of the wheel assemblies 22A to 22D not shown or discussed in detail herein may include, but are not limited to, other types of irrigation systems such as lateral irrigation systems, other types of agricultural equipment such as trucks, carts, implements, etc., or other types of vehicles such as buses, trucks, and automobiles. However, embodiments of the present invention are particularly well-suited for irrigation systems and other vehicles or systems that travel on unpaved or unfinished surfaces.

Referring now to Figures 2-4, a wheel assembly 22A constructed in accordance with an embodiment of the present invention is illustrated. Wheel assembly 22A generally includes a rigid wheel 30 and an airless, flexible tire 32 mounted thereon. Rigid wheel 30 includes a central hub 34 and a plurality of tire supports 36. Central hub 34 is configured to be mounted to or secured to the axle of mobile support tower 18A. Tire supports 36 extend radially outward from central hub 34 and are annularly spaced apart from one another to form recesses 38 between the tire supports. Recesses 38 may be distinct or may extend only slightly inward relative to tire supports 36. For example, in one embodiment, rigid wheel 30 has a polygonal shape, wherein tire supports 36 are vertices of the polygon and the areas between tire supports 36 are edges of the polygon. Tire supports 36 may be mounting bosses or other radially extending protrusions, or may be separate components, such as mounting elements, that are radially attached to central hub 34 via fasteners or interlocking geometry. Rigid wheel 30 may include between six and twenty tire supports 36. In one embodiment, the rigid wheel 30 includes ten tire supports 36 .

The airless flexible tire 32 is configured to be mounted on the rigid wheel 30 and generally includes a circular belt 40, a plurality of drive lugs 42, and a plurality of traction lugs 44A to 44C. The circular belt 40 includes an inner face 46, an outer face 48, and left and right side walls 50 and 52 extending between the inner face 46 and the outer face 48. The circular belt 40 may also include reinforcing elements such as fabric webbing or an endless steel belt that limit stretching of the airless flexible tire 32 and reinforce the airless flexible tire.

The drive lugs 42 extend radially inward from the inner face 46 of the round belt 40 and are annularly spaced apart from one another to engage the tire support 36 of the rigid wheel 30. The drive lugs 42 form a plurality of annularly spaced rigid high torque points 54 on the airless flexible tire 32 near the tire support 36 of the rigid wheel 30. A primary objective of the present invention is to reduce the high torque generated at the high torque points 54 or to equalize the torque generated by the wheel assembly 22A, as explained in more detail below. The drive lugs 42 can be integrally formed with the round belt 40 and can include complementary geometric structures, such as H-shaped ribs, for securing the airless flexible tire 32 to the rigid wheel 30.

Traction lugs 44A-44C extend radially outward from outer face 48 of round belt 40 and are annularly offset from drive lugs 42 to be positioned between tire supports 36 of the rigid wheel. Traction lugs 44A-44C, together with the base portion of round belt 40, form a plurality of annularly spaced flexible segments 56 on airless, flexible tire 32. The flexible segments are configured to deflect radially inward when traction lugs 44A-44C engage ground surface 100. Traction lugs 44A-44C may include a central traction lug 44A and/or offset traction lugs 44B, 44C. Central traction lug 44A is positioned equidistant between adjacent drive lugs 42 and includes a distal surface 58 and a plurality of side surfaces 60. Distal surface 58 may be substantially horizontal (i.e., perpendicular to a radial axis extending through central traction lug 44A) and/or symmetrical about the radial axis. The side surfaces 60 may be drafted at different angles to maintain traction as the airless flexible tire 32 rolls over the ground 100. The center traction lug 44A may be taller than the offset traction lugs 44B, 44C.

The offset traction lugs 44B, 44C are positioned on either side of the central traction lug 44A or otherwise offset between adjacent drive lugs 42 and are substantially identical, so only the offset traction lug 44B will be described in detail. The offset traction lug 44B includes a distal surface 62 and a plurality of side surfaces 64. The distal surface 62 can taper or bevel at an angle between 1 and 45 degrees from a radial axis extending through the offset traction lug 44B toward the nearest drive lug 42. As the airless flexible tire 32 rolls over the ground 100, the side surfaces 64 can extend at different angles to maintain traction. The offset traction lug 44B can extend at an angle between 1 and 45 degrees from the radial axis toward the nearest drive lug 42.

The traction lugs 44A-44C may be formed into a face-on traction lug pattern and may have other properties that combine the above features. For example, the traction lugs 44A-44C may be formed into a directional or non-directional Z-shaped tread pattern, a zigzag pattern, an angled pattern, a curved or straight pattern, or any other suitable tread pattern to improve traction and reduce soil erosion.

In use, as the rigid wheel 30 traverses a path along the ground 100, the airless flexible tire 32 engages the compliant soil layer. More specifically, as the flexible section 56 deflects into the recesses 38 between the tire supports 36, the tire supports 36 of the rigid wheel 30 push the high torque points 54 into the soil, forming a generally alternating peak-to-valley corrugated pattern. As the flexible section 56 is pushed into the recesses 38, the central traction lug 44A grips the peaks of the corrugated pattern, and the offset traction lugs 44B, 44C grip the sides of these peaks. As the airless flexible tire 32 rolls over the ground 100, the drafting side surfaces 60, 64 of the traction lugs 44A-44C maintain traction.

Because flexible section 56 is curved into a concave or arched shape, each pulling lug 44A-44C is urged radially inward depending on its position on flexible section 56. For example, because central pulling lug 44A is positioned at the center of flexible section 56, it is urged radially inward with little rotation. When rotating at least partially about the proximal high torque point 54, offset pulling lugs 44B, 44C are urged radially inward less than central pulling lug 44A. Due to the angle at which offset pulling lugs 44B, 44C extend from flexible section 56, offset pulling lugs 44B, 44C become substantially upright relative to ground surface 100 when rotating about the proximal high torque point 54. Simultaneously, due to the angle of distal end surface 62 relative to flexible section 56, distal end surfaces 62 of offset pulling lugs 44B, 44C become substantially level with ground surface 100.

Each traction lug 44A-44C has an effective height that is determined by its actual height, the angle at which traction lugs 44A-44C extend relative to the radial axis, the angle of distal surfaces 58, 62 of the traction lugs, and the amount by which flexible section 56 deflects near traction lugs 44A-44C. For example, central traction lug 44A may be taller than offset traction lugs 44B, 44C, but flexible section 56 deflects inwardly more near central traction lug 44A than near offset traction lugs 44B, 44C. Thus, the effective heights of traction lugs 44A-44C may be substantially equal. Because high torque point 54 does not deflect inwardly, traction lugs 44A-44C are also spaced apart from high torque point 54. In this manner, traction lugs 44A-44C at least partially equalize the rolling radius of wheel 30, reducing the torque generated near high torque point 54. In one embodiment, traction lugs 44A-44C achieve a uniform rolling radius for wheel 30 as airless flexible tire 32 passes over ground 100, such that the traction lug soil impression has a consistent depth. Alternatively, traction lugs 44A-44C may form a sinusoidal profile or any other suitable profile in the soil.

The airless, flexible tire 32 described above provides several advantages over conventional airless tires. For example, the traction lugs 44A-44C at least partially equalize the rolling radius of the wheel 30, which reduces the torque generated at the high torque point 54. The traction lugs 44A-44C form a ripple profile in the soil, which helps prevent erosion. The traction lugs 44A-44C can also form a sinusoidal profile or any other suitable profile, which further limits soil erosion. The traction lugs 44A-44C are spaced apart from each other by at least half the lug width to improve soil loss when the traction lugs 44A-44C are not in contact with the ground 100. As the airless, flexible tire 32 rolls over the ground 100, the side surfaces 60, 64 of the traction lugs 44A-44C are drafted at different angles to maintain traction.

While the present invention has been described with reference to the embodiments shown in the accompanying drawings, it should be noted that equivalents may be employed and substitutions may be made herein without departing from the scope of the invention as set forth in the claims.

Having thus described various embodiments of the present invention, what is claimed as new and desired to be protected by Letters Patent includes the following.

Claims (16)

1. A pneumatic flexible tire for covering a wheel, the wheel having a plurality of annularly spaced and outwardly extending tire supports, the pneumatic flexible tire comprising: A circular belt having an inner surface, an outer surface, and a left side wall and a right side wall located between the inner surface and the outer surface; Multiple annularly spaced drive lugs, extending inward from the inner surface of the circular belt, and each drive lug configured to align and engage with one of the tire supports on the wheel to form multiple annularly spaced, rigid, high-torque points on the airless flexible tire; and Multiple annularly spaced traction lugs extend outward from the outer side of the circular belt. The traction lugs are annularly offset from the drive lugs and positioned between the tire supports, thereby forming multiple annularly spaced flexible sections on the airless flexible tire that can be radially deflected inward when the traction lugs engage the ground. Each traction lug has an effective height corresponding to the amount of radial inward deflection of the airless flexible tire, such that the rolling radius of the wheel is at least partially uniform to reduce the amount of torque generated at the high torque point. The traction lugs are grouped such that each group includes: The central traction lug is equidistantly and annularly spaced from the adjacent driving lug; and Two offset traction lugs are circumferentially spaced apart on either side of the central traction lug, each offset traction lug having a distal surface, the distal surface of each offset traction lug being angled toward the nearest drive lug so that when the distal surface contacts the ground at the bottom of the tire rotation and the airless flexible tire deflects inward, the distal surface is substantially at the same level as the ground. 2. The airless flexible tire as claimed in claim 1, wherein each set of traction lugs includes a single central traction lug circumferentially spaced from the adjacent drive lugs and two offset traction lugs circumferentially spaced from both sides of the central traction lug. 3. The airless flexible tire of claim 2, wherein the offset traction lug extends from the radial axis at an angle between 1 degree and 45 degrees, such that the offset traction lug extends perpendicularly to the ground when the distal surface of the offset traction lug contacts the ground and the airless flexible tire deflects inward. 4. The airless flexible tire of claim 1, wherein the traction lug has a side surface that extends at different angles to maintain traction with the ground. 5. The airless flexible tire of claim 1, wherein the traction lug is configured to form a corrugated profile in the soil of the ground to limit soil erosion. 6. The airless flexible tire of claim 1, wherein the traction lug is configured to form a sinusoidal profile in the soil of the ground to limit soil erosion. 7. The airless flexible tire of claim 1, wherein the traction lugs are spaced apart from each other by a distance of at least half the width of the traction lugs to improve soil erosion when the traction lugs are not in contact with the ground. 8. A wheel assembly for traversing a path along a ground surface having a soil layer, the wheel assembly comprising: A rigid wheel having a plurality of annularly spaced and outwardly extending tire supports; and a pneumatic flexible tire comprising: A circular belt having an inner surface, an outer surface, and a left side wall and a right side wall located between the inner surface and the outer surface; Multiple annularly spaced drive lugs, extending inward from the inner surface of the circular belt, and each drive lug configured to align and engage with one of the tire supports on the wheel to form multiple annularly spaced rigid high-torque points on the airless flexible tire; and Multiple annularly spaced traction lugs extend outward from the outer side of the circular belt. These traction lugs are annularly offset from the drive lugs and positioned between the tire supports, thereby forming multiple annularly spaced flexible sections on the airless flexible tire that radially deflect inward when the traction lugs engage the ground. Each traction lug has an effective height corresponding to the amount of radial inward deflection of the airless flexible tire, such that the rolling radius of the wheel is at least partially uniform to reduce the amount of torque generated at high torque points. The traction lugs are grouped such that each group includes: The central traction lug is equidistantly and annularly spaced from the adjacent driving lug; and Two offset traction lugs are circumferentially spaced apart on either side of the central traction lug, each traction lug having a distal surface. The distal surface of each of the bias traction lugs is angled toward the nearest drive lug so that when the distal surface contacts the ground at the bottom of the tire rotation and the airless flexible tire deflects inward, the distal surface is substantially at the same level as the ground. 9. The wheel assembly of claim 8, wherein the tire support is a mounting element, and the drive lug forms an H-shaped rib to engage the mounting element. 10. The wheel assembly of claim 8, wherein the wheel has a polygonal shape such that the tire support forms the vertices of the polygon. 11. The wheel assembly of claim 8, wherein each group includes a central traction lug circumferentially spaced from adjacent drive lugs, and on either side of the central traction lug there are one and only two circumferentially spaced offset traction lugs. 12. The wheel assembly of claim 11, wherein the offset traction lug extends from the radial axis at an angle between 1 degree and 45 degrees, such that when the distal surface of the offset traction lug contacts the ground and the airless flexible tire deflects inward, the offset traction lug extends perpendicularly to the ground. 13. The wheel assembly of claim 11, wherein the traction lug has a side surface that extends at different angles to maintain traction with the ground. 14. The wheel assembly of claim 8, wherein the traction lug is configured to form a corrugated profile in the soil of the ground to limit soil erosion. 15. The wheel assembly of claim 8, wherein the traction lug is configured to form a sinusoidal profile in the soil of the ground to limit soil erosion. 16. A wheel assembly for traversing a path along a ground surface having a soil layer, the wheel assembly comprising: A rigid polygonal wheel having a plurality of annularly spaced and outwardly extending tire supports forming vertices of the polygon; and A pneumatic flexible tire, wherein the pneumatic flexible tire is mounted on a center hub, and the pneumatic flexible tire comprises: A circular belt having an inner surface, an outer surface, and a left side wall and a right side wall located between the inner surface and the outer surface; Multiple annularly spaced drive lugs, extending inward from the inner surface of the circular belt, and each drive lug configured to align and engage with one of the tire supports on the wheel to form multiple annularly spaced rigid high-torque points on the airless flexible tire; and Multiple annularly spaced traction lugs extending outward from the outer side of the circular belt, the traction lugs being divided into multiple groups, each group being annularly offset from the drive lugs and comprising: The central traction lug is equidistant from the adjacent driving lug; and Two offset traction lugs are circumferentially spaced apart from the central traction lug. These offset traction lugs extend from the radial axis at an angle between 1 degree and 45 degrees, such that they extend perpendicular to the ground when the airless flexible tire deflects. Each traction lug has an effective height corresponding to the amount by which the airless flexible tire deflects radially inward near the traction lug when the traction lug engages the ground, such that the rolling radius of the wheel is at least partially uniform to reduce the amount of torque generated at the high torque point. The traction lugs are grouped such that each group includes: The central traction lug is equidistantly and annularly spaced from the adjacent driving lug; and Two offset traction lugs are circumferentially spaced apart on either side of the central traction lug, each traction lug having a distal surface. The distal surface of each of the bias traction lugs is angled toward the nearest drive lug so that when the distal surface contacts the ground at the bottom of the tire rotation and the airless flexible tire deflects inward, the distal surface is substantially at the same level as the ground.