Background of the Invention Tire engineers have historically attempted to build very durable casing structures that can survive the severe driving conditions that the vehicle operators put the tires through.

Early on tires were very heavy and employed many layers or plies of bias cord. The primary objective was to simply retain the air and avoid a flat or deflation.

Through a process of endless research to develop more durable and better tire constructions new materials and better designs have been developed.

The introduction of the radial tire made it practical to develop tires having as few as one carcass ply. The ply was contained radially by a belt structure. To enhance the durability of the tire these belt structures evolved to become primarily steel reinforced. These steel reinforced belts yielded and currently provide a very durable structure.

These steel belted tires have many benefits that make their use attractive. The steel cords are not heat sensitive that is their physical properties are pretty much constant regardless of the tire's operating temperature. The steel cords are substantially inextensible and the cords can be made very high strength with fine filaments that have excellent fatigue resistance. Nevertheless these steel corded belts in tires have resulted in the need to add rubber gauge directly above the belts in the area commonly referred to as the undertread, in the belt layers themselves and in the areas of the belt edges, all in an attempt to

keep these steel cords from becoming exposed or structurally separating at the edges. Furthermore, the glass reinforced cord has a tenacity of 10 gr/denier compared to steel cord used in belts having 4 gr/denier.

The resultant effect has been that the steel belted radial tires are in fact heavier using more rubber in the tread area and in the tire's shoulders. It is precisely in these areas that a large part of the tire's tread wear performance and sensitivity to rolling resistance must be the highest. The more rubber in this area the higher the hysertesis effects and higher the temperatures under running conditions.

It is now an object of tire designers to develop tires that generate lower car fuel consumption. This can be achieved by designing cool running tires that have low mass and low rotational inertia while increasing the tire's handling performance and treadwear, furthermore, the engineer must insure that the tire's footprint and the contact patch of the tread has a uniform pressure distribution in order to achieve uniform wear.

With the advent of high performance tires having very low aspect ratios the use of belt structures having overlays of synthetic cords of nylon or aramid has been common. To further achieve high speed performance the tread thickness has been kept at a minimum. Thick tread mass at high speeds simply want to fly off the tire. As these tires are pushed to the engineer's known tire design limit he must rethink the entire parameters of the tire. In some cases this means going back and reanalyzing the concepts that were used in the past but were abandoned as a result of those in the art pursuing a different path.

One such approach that heretofore had lost favor among tire engineers was the use of fiberglass belts

which although a very good material for belts lost favor when steel belts were introduced. The primary downfall of fiberglass belts was their apparent lack of durability.

Even in the bias tires of the 1970's the use of fiberglass breakers had technical concerns. In U.S.

Patent No. 3,762,458 issued October 2, 1973, to Yoshida, et al., stated that "Glass is superior to organic fiber cord in the heat resistance, dimensional stability and modulus of elasticity and when rubber is reinforced with glass cord and used as a breaker layer of a pneumatic tire, the tire is excellent in various properties, particularly is excellent in the abrasion resistance (road test) and cornering power." Yoshida et al., then goes into detail as to why fiberglass cords were being disfavored in their use as breaker cords. He cites three serious drawbacks of the use of fiberglass breakers.

"Firstly, when a car is running, dynamic bending trans formation and impact transformation of the tire occurred due to the road surface condition, and the glass cords are broken or crushed.

Secondly, in general, foreign materials, such as nails, glass pieces and gravels, are penetrated into the tire and reached its breaker layer during the use of the tire, particularly at the end of the use. In this case, if the tire has a breaker layer composed of conventional organic fibers, such as nylon, rayon, polyester and vinylon (polyvinyl alcohol) fibers, etc., breakage of the tire occurs only at the portion to which the foreign materials have been penetrated. On the contrary, if the tire has a glass cord breaker layer, the glass cords are crushed by the penetrated foreign materials and the breakage of the glass cords extends along the glass cord breaker layer. This is a cause of serious troubles.

In order to solve these drawbacks, there has been tried to arranged organic fiber cords, such as nylon cords, on he tread side of the glass cord breaker layer.

However, a satisfactory result has not hitherto been obtained.

In addition to these drawbacks of glass cord, the inventors further have found a third drawback of glass cord, which is peculiar to glass cord and does not occur in organic fiber cord.

That is, in the vulcanization step of tire, the following step may be carried out. Namely, a tire is vulcanized at a high temperature and under a high pressure, and then the tire is taken out into an atmosphere at room temperature and under atmospheric pressure, and thereafter the tire is applied with air pressure to the inner side under a high pressure to stabilize the dimension of the tire. When the tire is taken out into the atmosphere at room temperature, cords composed of organic fibers other than glass fiber, such as rayon, nylon, vinylon and polyester fibers, etc., which are used as a reinforcing material of tire, that is, used in a carcass arranged on the inner side of breaker, are highly shrunk. As the result, glass cord breaker arranged directly adjacent to the rubber coated organic fiber cord layer (carcass) is compressed violently, and glass filaments constituting the glass cord of the breaker are compressed to decrease their tenacity and are broken during the car is running.

For instance, in a tire composed of 2 kinds of layers of a carcass layer reinforced with organic fiber cord and a glass cord breaker, glass cords constituting a glass cord breaker layer arranged on the carcass side are inferior in the tenacity to glass cords constituting another glass cord breaker layer arranged on the tread side.

Further, when organic fiber cords having different shrinkabilities, for example, nylon cord or rayon cord is used as a carcass cord, the nylon cord having a higher shrinkability decreases the tenacity of glass cord more than the rayon cord.

Further, even in the vulcanization treatment of conventional bias-belted tires in which rubber coated organic fiber cord layer, such as rubber coated nylon cord layer, is arranged on the tread side of the glass cord breaker, the above described phenomenon occurs between the glass cord breaker and the rubber coated organic fiber cord layer, whereby glass filaments are broken. Because, when the tire is cooled, the above described organic fiber cord shrinks considerably." These three problems were allegedly solved by Yhoshida et al., as quoted below: "Among the above described three drawbacks of the tire having the glass cord breaker layer, the first drawback has already been solved by the inventors. That is, in order to decrease the bending transformation and impact transformation of glass cord, a short cut fiber reinforced rubber layer is arranged on the tread side of the glass cord breaker layer. In order to solve the second drawback, that is, the problem of plunger resistance against foreign materials, the inventors have confirmed that the arrangement of the short cut fiber reinforced rubber layer on the tread side of the glass cord breaker layer has a higher effect than the arrangement of a sole rubber layer or a rubber coated cord layer.

Furthermore, in order to solve the third drawback, the inventors have found that the following arrangement is more effective. That is, the glass cord breaker layer is not arranged directly adjacent to organic fiber cords having a high shrinkability, but such a layer that

has a low shrinkability and does not transmit the shrinkage of the organic fiber cords to the glass cord breaker layer is arranged between the rubber coated organic fiber cord layer (carcass) and the glass cord breaker layer." Thus, Yoshida et al., attempted to retain the use of fiberglass breakers in bias tires.

The use of fiberglass belts in radial tires was even more challenging. In U.S. patent to Christian M.

L. L. Bourcier de Carbon of France, de Carbon explains "Radial carcass tires essentially comprise a radial carcass, made up of curved members which are straight in the center planes of the cover, in combination with a non-extensible belt comprising a reinforcement which is flexible in the radial direction (the direction perpendicular to the tread surface) but has high longitudinal and transverse rigidity (i.e., in directions parallel to the tread surface), the non- extensible belt being automatically tensioned by the internal pressure and thus having a considerable equatorial binding effect on the curved members of the carcass, even when the pneumatic tire is at rest and is not subjected to any crushing load." DeCarbon' s solution to the problem of radial tire belt structures was the use of flattened cords having a width of about 1 mm, the highly flattened cords being of steel plastic or glass fiber oriented at cross angles of about 450 to 600. As can easily be appreciated such solutions were very complicated and ultimately lost any commercial interest due to their complexity and the concurrent simpler success of steel belts.

The present invention demonstrates that the use of fiberglass belts can again be made commercially acceptable if the fiberglass is employed with a combination of other components that insure that the

glass cords are not damaged during manufacture by insuring that the thermal shrinkage differentials created during vulcanization, cooling and subsequent reinflation are not transmitted to the glass cords. The fiberglass belts not only are commercially acceptable but also can provide surprisingly beneficial improvements in tire weight and reduced rolling resistance.

Summary of the Invention A radial ply tire 10 exhibiting very light weight and low rolling resistance has an aspect ratio in the 0.2 to 0.8 range. The tire 10 has a pair of parallel annular bead cores 26; one or more radial carcass plies 38, at least one radial carcass ply 38 being wrapped around said bead cores 26; a belt structure 36 disposed radially outwardly of said one or more radial carcass ply 38 in a crown area of the tire 10; and an overlay 59 having a width coinciding substantially with the width of the belt structure 36. A tread 12 is disposed radially outwardly of said overlay 59 and a sidewall 20 is disposed between the tread 12 and said beads 26.

The overlay 59 has filaments or cords 70, the cords 70 being selected form a group of materials, the group being rayon, PET, aramid, PEN, or PVA embedded in an elastomer. The belt structure 36 is made from two fiberglass cord reinforced layers 50,51 having cord angles in the range of 180 to 260, preferably about 220.

The layers 50,51 are single cut layers requiring no folded lateral edges.

The overlay 59 is preferably spirally wound radially outward of and adjacent to the belt structure 36. The overlay 59 being made from a continuous strip of reinforcing tape having a width of h inch to 1d inches having 4 to 45 parallel reinforcing filaments or cord 70 embedded therein.

In the preferred embodiment the overlay cords 70 are aramid, however, cords of high tensile strength, low thermal shrinkage such as rayon, PEN, PET or PVA can be used as well.

The tire 10 according to the invention has a very thin undertread 13, the undertread 13 being measured from the radially outer surface of the cords 70 of the overlay 59 to a circumferential groove of full depth.

The undertread 13 thickness (t) is less than 2 mm preferably above 1 mm.

To enhance handling performance the tire 10 employs a hard apex 46 extending radially outwardly of each bead core 26 and adjacent the ply 38. The apex 46 have a shore D hardness greater than 50.

To enhance lateral stability the tire 10 it can employ two sidewall inserts, one insert being in each sidewall 20. Each sidewall insert has two layers 52,53 of bias cord reinforcements. The cords of the first layer 52 oriented equal but opposite to the cords of the second layer 53, the two layers 52,53 being interposed between the apex 46 and the turnup 32 of the carcass ply 38. The cords of each layer are oriented at an angle of 250 to 600 relative to the radial direction. Preferably, the first and second layer 52,53 has a radially inner end 54 and a radially outer end 55, the respective ends 54,55 of one layer being staggered relative to the ends 54,55 of the opposite layer. The radially outer end 55 of one layer is located at about one-half of the tire's section height SH or at location h as shown.

The tire 10 further has a noise dampening gumstrip 42 lying below a belt edge and extending to about 50% of the section height SH of the tire 10.

The cords 41 of the one or more carcass plies 38 can be selected from the group of rayon, nylon, PEN,

PET, steel, or aramid. The preferred tire 10 employed one rayon carcass ply 38.

The tire 10 using the novel combination described above can be made very light weight compared to conventional tires.

The inventive tire 10 can demonstrate excellent performance, particularly high speed handling with the added benefit of very low rolling resistance.

Brief Description of the Drawing Fig. 1 is a cross-sectional view of the preferred embodiment tire 10 according to the present invention.

Definitions "Aspect Ratio" means the ratio of its section height to its section width.

"Axial" and "axially" means the lines or directions that are parallel to the axis of rotation of the tire.

"Bead" or "Bead Core means generally that part of the tire comprising an annular tensile member, the radially inner beads are associated with holding the tire to the rim being wrapped by ply cords and shaped, with or without other reinforcement elements such as flippers, chippers, apexes or fillers, toe guards and chafers.

"Belt Structure11 or "Reinforcing Belts" means at least two annular layers or plies of parallel cords, woven or unwoven, underlying the tread, unanchored to the bead, and having both left and right cord angles in the range from 17~ to 270 with respect to the equatorial plane of the tire.

"Circumferential" means lines or directions extending along the perimeter of the surface of the annular tread perpendicular to the axial direction.

"Carcass" means the tire structure apart from the belt structure, tread, and undertread, but including the beads.

"Casing" means the carcass, belt structure, beads, sidewalls and all other components of the tire excepting the tread and undertread.

"Chafers" refers to narrow strips of material placed around the outside of the bead to protect cord plies from the rim, distribute flexing above the rim.

"Cord" means one of the reinforcement strands of which the plies in the tire are comprised.

"Equatorial Plane (EP)?? means the plane perpendicular to the tire's axis of rotation and passing through the center of its tread.

"Footprint" means the contact patch or area of contact of the tire tread with a flat surface at zero speed and under normal load and pressure.

"Innerliner" means the layer or layers of elastomer or other material that form the inside surface of a tubeless tire and that contain the inflating fluid within the tire.

"Normal Inflation Pressure" means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.

"Normal Load" means the specific design inflation pressure and load assigned by the appropriate standards organization for the service condition for the tire.

"Ply" means a layer of rubber-coated parallel cords.

"Radial" and "radially" mean directions radially toward or away from the axis of rotation of the tire.

"Radial Ply Tire" means a belted or circumferentially-restricted pneumatic tire in which at least one ply has cords which extend from bead to bead are laid at cord angles between 650 and 900 with respect to the equatorial plane of the tire.

"Section Height" means the radial distance from the

nominal rim diameter to the outer diameter of the tire at its equatorial plane.

"Section Width" means the maximum linear distance parallel to the axis of the tire and between the exterior of its sidewalls when and after it has been inflated at normal pressure for 24 hours, but unloaded, excluding elevations of the sidewalls due to labeling, decoration or protective bands.

"Shoulder" means the upper portion of sidewall just below the tread edge.

"Sidewall" means that portion of a tire between the tread and the bead.

"Tread Width" means the arc length of the tread surface in the axial direction, that is, in a plane parallel to the axis of rotation of the tire.

Detailed Description of the Invention The tire 10 according to the present invention employs a unique structure. Tire 10 as illustrated in Fig. 1 is a radial passenger or light truck tire; the tire 10 is provided with a ground-engaging tread portion 12 which terminates in the shoulder portions at the lateral edges 14,16 of the tread 12 respectively. A pair of sidewall portions 20 extends from tread lateral edges 14,16 respectively and terminates in a pair of bead regions 22 each having an annular inextensible bead core 26 respectively. The tire 10 is further provided with a carcass reinforcing structure 30 which extends from bead region 22 through one sidewall portion 20, tread portion 12, the opposite sidewall portion 20 to bead region 22. The turnup ends 32 of at least one radial ply 38 carcass reinforcing structure 30 are wrapped about bead cores 26 and extend radially outwardly to a terminal end 33. The turnup 32 may end at about the radial location of the maximum section width in the embodiment of Fig. 1. The tire 10 may include a

conventional innerliner 35 forming the inner peripheral surface of the tire 10 if the tire is to be of the tubeless type. In the preferred tire 10 the innerliner 35 is made of 100% bromobutyl.

As shown in Fig. 1 the tire 10 can employ a single synthetic ply wrapped over the bead core 26 and extending to a high turnup end 33 located at about the radial location of the maximum section diameter (h).

Placed circumferentially about the radially outer surface of carcass reinforcing structure 30 beneath tread portion 12 is a tread reinforcing belt structure 36. In the particular embodiment illustrated, belt structure 36 comprises two cut belt plies 50,51 and the cords 80 of belt plies 50,51 are oriented at an angle of about 22 degrees with respect to the mid-circumferential centerplane of the tire.

The cords 80 of belt ply 50 are disposed in an opposite direction to the mid-circumferential centerplane and from that of the cords 80 of belt ply 51. However, the belt structure 36 may comprise any number of belt plies and the cords 80 may be disposed at any desired angle preferably in the 180 to 260 range. An important feature of the layers 50,51 is that each layer 50,51 is a single cut layer, neither layer having folded lateral edges. The belt structure 36 provides lateral stiffness across the belt width so as to minimize lifting of the tread 12 from the road surface during operation of the tire 10. In the embodiments illustrated, this is accomplished by making the cords 80 of belt plies 50,51 of fiberglass and preferably fiberglass 660/1Tex having a density of 15-25 EPI construction.

The carcass reinforcing structure 30 comprises at least one reinforcing ply structure 38. In the particular embodiment illustrated in Fig. 1, there is

provided a reinforcing ply structure 38 with a radially outer ply turnup 32, this ply structure 38 has preferably one layer of parallel cords 41. The cords 41 of reinforcing ply structure 38 are oriented at an angle of at least 75 degrees with respect to the mid- circumferential centerplane CP of the tire 10. In the particular embodiment illustrated, the cords 41 are oriented at an angle of about 90 degrees with respect to the mid-circumferential centerplane CP. The cords 41 may be made of any material normally used for cord reinforcement of rubber articles, for example, and not by way of limitation, rayon, nylon and polyester, aramid or steel. Preferably, the cords are made of material having a high adhesion property with rubber and high heat resistance.

For the carcass cords 41, organic fiber cords with an elastic modulus in the range of 250 to 1400 kgf/sq mm such as nylon 6, nylon 6-6, rayon, polyester or high- modulus cords, commonly are used. In the case of 340- to-2100dTex such fiber cords are used preferably at a density of 17 to 30 EPI.

Other high modulus fiber include aramid, vinyl on, PEN, PET, PVA, carbon fiber, glass fiber, polyamides.

Alternatively, steel cords of very high tensile strength steel having fine diameter filaments exhibiting excellent fatigue resistance could be used. In the particular preferred embodiment illustrated, the cords 41 are made from rayon. The cords 41 have a modulus E of X and a percent elongation of Y. The preferred rayon cord 41 has X values in the range of at leaso 10 GPa and percent elongations in the range commonly found in the specific material of the cord.

As further illustrated in Fig. 1, the bead regions 22 of the tire 10 each have an annular substantially inextensible first and second bead cores 26

respectively.

The bead core is preferably constructed of a single or monofilament steel wire continuously wrapped. In the preferred embodiment 0.038 inch (0.97 mm) diameter high tensile steel wire is wrapped in four layers radially inner to radially outer of four wires, respectively, forming a 4x4 construction.

Located within the bead region 22 and the radially inner portions of the sidewall portions 20 are high modulus elastomeric apex inserts 46 disposed between carcass ply reinforcing structure 38 and the turnup ends 32, respectively. The elastomeric apex inserts 46 extend from the radially outer portion of bead cores 26 respectively, up into the sidewall portion gradually decreasing in cross-sectional width. The elastomeric inserts 46 terminate at a radially outer end at a distance G radially inward of the maximum section width of the tire at the location (h) as shown in Fig. 1. In the particular embodiment illustrated, the elastomeric apex inserts 46 each extend, from their respective bead cores 26 to a distance G of approximately 25 percent (25%) of the tire's section height.

For the purposes of this invention, the maximum section height SH of the tire shall be considered the radial distance measured from the nominal rim diameter NRD of the tire to the radially outermost part of the tread portion of the tire. Also, for the purposes of this invention, the nominal rim diameter shall be the diameter of the tire as designated by its size.

In a preferred embodiment of the invention the bead regions 22 further includes at least one cord reinforced member 52,53 located between the apex insert 46 and the ply turnup end 32. The cord reinforced member or members 52,53 have a first end 54 and a second end 55. The first end 54 is axially and radially inward of the second end

55. The cord reinforced member or members 52,53 increase in radial distance from the axis of rotation of the tire 10 as a function of distance from its first end 54. In the illustrated Fig. 1, the cord reinforced member comprises two components 52,53 having a width of about 4 cm. The axially inner component 52 has a radially inner end 54 that is radially at or slightly above the first and second bead cores 26. The axially outer component 53 has a radially inner end that is radially outward of the outer surface of the bead core 26 by about 1 cm. The axially inner and axially outer components 52,53, preferably have rayon, nylon, aramid or steel cord reinforcement, in the preferred embodiment tire nylon 1400/2dTex cords were used. The second end 55 of the cord reinforced member 53 is located radially outward of the bead core 26 and the termination 33 of the turnup end 32 of the first ply 38 and it is radially located at a distance at least 50% of the section height SH as measured from the nominal bead diameter.

The cords of members 52,53 are preferably inclined forming an included angle relative to the radial direction in a range from 250 to 75O, preferably 55O. If two members are employed, the cord angles are preferably equal but oppositely disposed. The cord reinforcement member 52,53 improves the handling characteristics of the tire 10 of the present invention. The members 52,53 greatly reduce the tendency for the car to oversteer, a significant problem encountered in conventional tires that are driven while uninflated or underinflated.

A fabric reinforced member 61 may be added to the bead regions 22 of the tire 10. The fabric reinforced member has first and second ends 62,63. The member is wrapped about the first ply 38 and the bead core 26.

Both the first and the second ends 62,63 extend radially

above and outward of the bead core 26.

The sidewall portions 20 of the preferred embodiment tire 10 are provided with a pair of first noise dampening fillers 42. The first noise dampening fillers 42 are employed between the innerliner 35 and the reinforcement ply 38. The first fillers 42 extend from under each belt edge in the shoulder region of tire 10 to radially inward of the reinforced member end 55.

As illustrated in the preferred embodiment of the invention as shown in Fig. 1, the sidewall portions 20 each include a first noise dampening filler 42 and an apex insert 46. The first fillers 42 are positioned as described above. The apex inserts 46 are located between the first ply 38 and the turnup ends 32 of ply 38 respectively.

For purposes of this invention, the maximum section width (SW) of the tire is measured parallel to the rotational axis of the tire from the axially outer surfaces of the tire, exclusive of indicia, adornment and the like. Also, for the purposes of this invention the tread width is the axial distance across the tire perpendicular to the equatorial plane (EP) of the tire as measured from the footprint of the tire inflated to maximum standard inflation pressure, at rated load and mounted on a wheel for which it was designed.

The tire 10 illustrated in Fig. 1 of the preferred embodiment tire has a fabric overlay layer 59 disposed about the tread reinforcing belt structure 36. For example, two ply layers ideally spirally wound having PEN, PET, PVA, rayon or aramid cords may be disposed above each reinforcing belt structures 36, the lateral ends extending past the lateral ends of the belt structures 36. Alternatively, a single layer of spirally wound reinforced fabric can be employed as an overlay. The preferred embodiment tire 10 employed

spirally wound aramid cords 70, of the flexten 1670/3dTex or more preferably 1100/2dTex. The aramid material has a substantially higher modulus of elasticity than nylon and accordingly results in a stronger tire reinforcement than two layers of nylon.

Nylon exhibiting high thermal shrinkage should be avoided because its use will damage the fiberglass cords 80 of the belts 50,51. Applicants have found that an increase in high speed capability can be achieved in a tire with the single layer of aramid overlay having at least 14 EPI, preferably about 17 EPI. Generally the use of aramid material in passenger tire applications is avoided due in part to the fact that the material exhibits poor noise properties that resonate sounds through the relatively thin sidewalls of the passenger tire. Applicants' tire of the present invention employs a noise dampening insert 42 in the sidewalls 20 which noticeably dampen tire generated noises. These noise dampening sidewalls 20 permit the use of an aramid overlay without experiencing unacceptable noise levels.

The cords 80 of the overlay 59 alternatively can be made of rayon, PET, PEN or PVA. A PEN filament having a density of 240dTex to 2200dTex can be employed, more preferably 1440/2dTex having both a yarn and cord twist of between 4 and 12 tpi, preferably 7Z/9S can be employed.

The apex insert fillers 46, as shown, can be made of one or two or more distinct elastomeric materials.

The preferred embodiments employed only one compound or material in the apex inserts 46 which extended from the bead core 26. The preferred apex insert material is very hard having a shore D hardness of 50 or more, preferably 50 to 55. The hardness of the insert 46 was achieved by crosslinked reinforcing resins mixed to a commonly known mixing procedure to achieve a high

hardness which permits a minimal amount of material to be used to form the apex insert 46.

The inserts 46 may alternatively be loaded with short fibers, which are preferably oriented at an angle of at least 45O to enhance the radial and lateral stiffness of the insert, preferably the fibers are radially oriented. Preferably the short fibers are made of textile or synthetic materials such as rayon, nylon, polyester or aramid. These short fibers can be radially directed or positioned at bias angles preferably at least 45O but should not be circumferentially extending.

Chafing of the tire 10 in the lower bead region radially outward of the carcass structure 30 adjacent the rim flange may be minimized, especially during use of the tire in an underinflated condition, by providing hard rubber chafer portion 60.

The belt structure 36 has belts 50,51 which preferably used fiberglass 660/1Tex at a density of 15 to 25 EPI. The belts 50,51 had a width of about 98% of the mold tread cord width commonly referred to as the tread arc width.

To further enhance the tire 10 performance and light weight features the tread 12 was constructed having a minimal gauge or thickness (t) of the undertread 13. Conventionally for high performance passenger tire the undertread is reduced to between 2 and 5 mm. The tire of the present invention had an undertread less than 2 mm, preferably about 1 mm as measured from the radially outer cords 70 of the overlay 59 to a full depth circumferential groove bottom as shown in Fig. 1.

To insure the inventive tire 10 reduced the inherent stresses created when molding a tire having fiberglass belts 50,51 it was determined that the mold should be wide and flat at the tread. The tread radius

of 315 mm and a tread cord width of 141 mm was evaluated with acceptable results. In a tire size of 195/65R15 91V, a tread radius of 914 mm and a tread cord width of 152 mm yielded most superior results. The inventors believe that a flat tread radius greater than 300 mm over a tread cord width of about 125 mm or more will provide acceptable results. More preferably the tread radius R should be greater than 500 mm for tread cord width of greater than 150 mm, most preferably R should be at least 750 mm. This wide flat tread arc permits the belt cords 80 to experience minimal thermal shrinkage distortion which could damage cords of the ply 51, adjacent the carcass ply 38. This in combination with the ply cords 41 of low thermal shrinkage and an overlay 59 of similar low thermal shrinkage means that the tire 10 can be manufactured and placed in use such that the fiberglass belts 50,51 will survive the exposure to thermal expansion and contraction.

A test tire 10 having a size 195/65R15 91V was made with the conventional steel belts the tire weight was 9.4 Kg. The same size tire made according to the present invention and has a weight of 7.2 Kg, depending on the tuning of the tire 10 the weight when employing the inventive concepts described above have yielded weights in the 6.9 te 7.4 Kg range.

This weight reduction in and of itself was a most beneficial improvement over the prior art since it reduces the kinetic energy contribution of the tire, decreasing both translation and rotational kinetic energy and thus reducing fuel consumption.

Additionally, the reduced weight of the unsprung tire mass allows the car manufactures to redesign the suspension with reduced weight components to improve car weight, performance and handling.

The tire of the present invention brought about a

10% rolling resistance improvement vs a classic construction made in the same mold with the same tread compound.

Treadwear improvements of 0 to 10% were observed in standard wear test of the tire 10 versus the conventional construction. The tire 10 was noticed to be less sensitive to wheel position wear. The shoulder wear of steering position and the centerline wear of the rear wheel position when lightly loaded were much less pronounced in the inventive tire 10 when compared to the prior art tires.

Flatspotting of the inventive tire was very much improved over prior art tires in terms of the amount of time required to recover disturbance free ride.

Flatspotting is a condition that commonly occurs when a vehicle after being driven is parked causing the warm tire to cool such that the structure has a locally flattened casing structure.

Most importantly the inventive tire has demonstrated excellent durability and has passed plunger, high speed V, road durability carcass fatigue, outdoor resiliometer, curb impact test, road plunger and legally required DOT and ECE R30 qualification tests.

While certain representative embodiments and details have been shown for the purpose of illustrating the invention, it will be apparent to those skilled in this art that various changes and modifications may be made therein without departing from the spirit or scope of the invention.