Patent Description:
Functions of a tyre on an automotive vehicle include providing sufficient traction for accelerating, driving, and braking; and providing adequate steering control particularly at high speeds. Traction is commonly referred to as grip and steering control as handling. Grip is affected also by the ground (e.g. a road surface) on which the tyre is commonly used. Winter tyres, which are intended for icy and snowy (wintry) roads, are commonly equipped with studs to improve grip on ice. However, studs of the studded tyres wear during use and the grip may become worse compared to new, unused studded tyres.

The patent application <CIT> discloses a pneumatic tyre, which includes land portions partitioned and formed by inclined grooves inclined with respect to a tyre circumferential direction. Stud pins are embedded in at least one of the land portions. The number of embedded stud pins embedded in a shoulder region is from <NUM> to <NUM> times the number of embedded stud pins embedded in a centre region. A protruding amount of the stud pins in the shoulder region is from <NUM> to <NUM> times the protruding amount of the stud pins in the centre region.

The international patent application <CIT> discloses a stud pin and a tyre comprising said stud pin. A stud pin includes a body embedded into the tread of a tyre, a tip that projects out from the leading end of the body, and a flange disposed on the base end of the body, wherein a groove is formed in the surface on the leading end of the tip, and the total area Sx of the tip and the area Sy of the groove when viewed in the direction of the central axis of the body satisfies the relationship <NUM> ≤ Sy / Sx ≤ <NUM>.

An aim of the present invention is to provide a studded tyre which provides for good grip within a reasonable lifetime of the tyre. In other words, the grip of the studded tyre is maintained at a good level also when the tyre has been in use for a long time.

According to a first aspect of the invention, a studded tyre is presented, comprising a tread having a plurality of tread blocks, a plurality of studs installed in at least some of the tread blocks, wherein studs at a centre area have higher protrusion from the surface of the tread block than studs in a shoulder area of the tyre.

The tread blocks may be arranged in a periodic fashion called as a pitch. In other words, similar sequence of such a group of tread blocks of one pitch may be repeated over the whole circumference of the tyre. In other words, each pitch includes a predetermined geometry of whole and/or partial tread blocks. The number of tread blocks in each pitch may vary in width across the tire. There may be several different pitches, with variable dimensions or geometry.

In accordance with an embodiment of the invention, the configuration of the studs is such that the protrusion of studs in the centre area is in a range from <NUM> to <NUM>, preferably <NUM> to <NUM>, most preferably <NUM> to <NUM> and the protrusion of studs in the shoulder areas is in a range from <NUM> to <NUM>, preferably <NUM> to <NUM>, most preferably <NUM> to <NUM> so that the studs at the centre area have higher protrusion than studs in the shoulder area.

According to an example of the invention, the protrusion of a majority of the studs in the centre area of the tyre is in the range from <NUM> to <NUM> and the protrusion of a majority of the studs in the shoulder area of the tyre is in the range from <NUM> to <NUM> so that the protrusion of the studs in the centre area are <NUM> or at least <NUM> higher than the protrusion of the studs in the shoulder area. According to another example, the average protrusion of the studs in the centre area of the tyre is in the range from <NUM> to <NUM> and the average protrusion of the studs in the shoulder area of the tyre is in the range from <NUM> to <NUM> so that the protrusion of the studs in the centre area are <NUM> or at least <NUM> higher than the protrusion of the studs in the shoulder area. According to yet another example, the protrusion of studs in the centre area is in the range from <NUM> to <NUM> and the protrusion of studs in the shoulder areas is in the range from <NUM> to <NUM>. According to still another example, the protrusion of studs in the centre area is in the range from <NUM> to <NUM> and the protrusion of studs in the shoulder areas is in the range from <NUM> to <NUM> so that the protrusion of the studs in the centre area are <NUM> or at least <NUM> higher than the protrusion of the studs in the shoulder area.

In accordance with an embodiment of the invention, the higher protrusion in the centre area is achieved by using in a centre area studs in which a pin of the stud is longer than in studs in the shoulder area.

In accordance with an embodiment of the invention, the higher protrusion in the centre area is achieved by using similar studs in both centre area and shoulder areas but using stud holes having different depths in the centre area than in the shoulder areas.

In accordance with an embodiment of the invention, the higher protrusion in the centre area is achieved by using longer studs in the centre area than studs in the shoulder area, although the pin of each stud may have substantially equal length.

Several embodiments of the invention are defined in the dependent claims.

Within this description the term tyre refers to a tyre configured to be used on a wheel of a car, especially a passenger car. In line with this, within this description, a road wear of the studded tyre is defined as the road wear in the test specified in the standard SFS7503:<NUM>:en, which concerns primarily tyres designed for vehicles in categories M1 and N1, as defined in the Consolidated Resolution on the Construction of Vehicles (R. <NUM>), document ECE/TRANS/WP. <NUM>/<NUM>/Rev. <NUM>, para. These categories are:.

The standard SFS7503:<NUM>:en specifies the test procedure in detail. On the general level, in the test, a vehicle equipped with the tyres to be tested is driven over test specimens (i.e. test stones) with specified speed for a specific number of times. The test requires that two identical tyres are tested simultaneously; they are used on one side of the vehicle in the test. According to the standard, a properly loaded vehicle is driven two-hundred times over the test stones at the speed of <NUM>/h. As both the front and rear wheel pass the test stones, there are a total of four hundred passes of the test tyres over the test stones; and these passes cause the test stones to wear. Road wear according to the standard SFS7503:<NUM>:en is the average weight loss of three test stone rows compensated by the weight loss of reference stones, if applicable. For further details refence is made to the standard. The average wear of test specimens is expressed in units of mass (i.e. in grams). The less the tyres wear the specimens, the less is the result (grams, g) of the test, and thus the less the tyres wear a regular road, too.

In the following the invention will be explained in more detail with reference to the appended drawings, in which.

<FIG> shows a studded tyre <NUM>. A studded tyre <NUM> comprises a tread <NUM> and multiple studs <NUM> provided in the tread <NUM>. Referring to <FIG>, the studs <NUM> have been installed into stud holes <NUM>. The stud holes <NUM> may be made to the tread <NUM> during vulcanization of the tyre. The studded tyre <NUM> is a tubeless tyre, i.e. functional on a rim and without an inner tyre.

Referring to <FIG>, the tread <NUM> of the studded tyre <NUM> comprises tread blocks <NUM> such that grooves <NUM> are arranged between the tread blocks <NUM>. In this description, a "rib" is considered as a large tread block <NUM> in the middle of the tyre <NUM> which can be regarded as a plurality of mutually connected tread blocks. For example, the tread of <FIG> include a central tread block <NUM> that extends over the entire circumference of the tread, even if such a tread block could be called a central rib. A tread <NUM> needs not comprise a tread block that extends circumferentially throughout the tread <NUM>. In addition, the tyre <NUM> comprises studs <NUM>, which have been installed into at least some of the tread blocks <NUM>. Referring to <FIG>, a stud <NUM> preferably comprises a pin <NUM>, and preferably each stud <NUM> of the tyre <NUM> comprises a pin <NUM>. Moreover, in the tyre <NUM>, at least the pins <NUM> of the studs <NUM> are exposed on the tread <NUM> (see e.g. <FIG> and <FIG>). The pins <NUM> are exposed so that studs have a protrusion P100 of a stud <NUM> measured from the tread <NUM>. The protrusion P100 is indicated in <FIG>. The protrusion P100 is measured in the radial direction +SR and from a planar surface defined by the radially outermost edges of the stud hole <NUM> into which the stud <NUM> has been installed. Naturally, the tread <NUM> itself defines the edges of the stud hole <NUM>.

Some measures of a tyre <NUM> are depicted in <FIG>. Within this description, the width W200 of the tyre <NUM>, as shown in <FIG>, refers to the "Section Width" as defined in the Standards Manual <NUM> of the European Tyre and Rim Technical Organization (ETRTO). The height H200 of the tyre <NUM> is also shown in <FIG>, and is defined as the "Section Height" in the ETRTO Standards Manual <NUM>. Correspondingly, the Section Width, i.e. the width W200 of the tyre <NUM> as defined herein (and in the ETRTO standards manual) is the linear distance between the outsides of the sidewalls of an inflated tyre excluding elevations due to labelling (markings), decoration, or protective bands or ribs. <FIG> also shows half of a cross section of a rim <NUM> onto which the tyre <NUM> has been installed.

In practice, the tyre width W200 is related to the size marking shown on the tyre <NUM>. In general, the size marking is shown on a tyre as w/hRr, wherein w denotes a width, h an aspect ratio and r a radius. According to the ETRTO standards manual, typical size markings refer to Design Width (i.e. the width W200 of the tyre <NUM>) and an overall diameter as shown in the Table <NUM> below:.

It is noted that Table <NUM> shows only some examples. A tyre may have a different size, in particular another aspect ratio than <NUM>, such as <NUM>, <NUM>, <NUM> or <NUM>.

<FIG> shows an example of a stud <NUM> which can be used with the studded tyre <NUM>. It should be noted that this is only an example and also other kinds of studs may be used. Moreover, the tyre <NUM> may comprise more than one kind of studs.

The direction Sz of <FIG> is a longitudinal direction of the stud, and the stud may be installed to the tread <NUM> such that the positive longitudinal direction +Sz is the radially outward direction +SR of the tyre (see e.g. <FIG>). A purpose of the stud <NUM> is to improve grip of the tyre <NUM> particularly on ice.

Referring to <FIG>, the stud <NUM> comprises a body <NUM> and a pin <NUM>. The body <NUM> comprises a bottom flange <NUM> and a second part <NUM>. The second part <NUM> is joined to the bottom flange <NUM> and extends in the longitudinal direction Sz of the stud <NUM> from the bottom flange <NUM>. The pin <NUM> protrudes from the second part <NUM> in the longitudinal direction Sz of the stud <NUM>. The pin <NUM> comprises hard metal or ceramic. In terms of Vickers hardness, the Vickers hardness of the pin <NUM> is higher than the Vickers hardness of the second part <NUM>.

As shown in <FIG>, the bottom flange <NUM> has a first cross-section on a plane (i) that has a normal in the longitudinal direction Sz of the stud, the first cross-section having a first area A140. Typically, as shown in <FIG>, the bottom flange <NUM> has the first cross-section on a plane that has a normal in the longitudinal direction Sz of the stud. Moreover, the bottom flange <NUM> has a profile shape extending at least a certain distance in the direction of the normal of the first cross-section. <FIG> shows the cross-section Ie of the bottom flange <NUM> of the stud of <FIG>, the cross-section Ie indicated in <FIG>. In such a case, the second part <NUM> extends straight. However, the second part <NUM> may extend in a curvilinear fashion. <FIG> shows the cross-section Id of the bottom flange <NUM> of the stud of <FIG>, the cross-section Id indicated in <FIG>. Also in that case, the second part <NUM> extends straight. However, the second part <NUM> may extend in a curvilinear fashion.

The pin <NUM> has a second cross-section on a plane that has a normal in the longitudinal direction Sz of the stud <NUM>, the second cross-section having a second area A110. <FIG> shows the cross-section Ib of the pin <NUM> of the stud of <FIG>, the cross-section Ib indicated in <FIG>. The first area A140 is greater than the second area A110.

To provide a good grip, the pin <NUM> should protrude from second part <NUM> sufficiently. A first height H110 which is the height that the pin <NUM> protrudes from the second part <NUM> (e.g. from an upper flange <NUM> of the second part <NUM>) is depicted in <FIG>, <FIG>. As shown in <FIG>, <FIG>, the second part <NUM> extends in the longitudinal direction Sz of the stud <NUM> from the bottom flange <NUM> to an interfacial point <NUM> between the second part <NUM> and the pin <NUM> and does not extend further in this direction. In <FIG>, a waist <NUM> and the upper flange <NUM> constitute the second part <NUM>.

The pin <NUM> and the second part <NUM> define the first height H110, which is the length the pin <NUM> protrudes from the interfacial point <NUM> in the longitudinal direction Sz to the extremal point <NUM> of the pin <NUM> in the longitudinal direction Sz of the stud. Thus, the pin <NUM> protrudes the first height H110 from the second part <NUM> of the stud; particularly from the interfacial point <NUM>.

For good grip, the first height H110 should be sufficient. However, if the first height H110 is excessive, the road wear caused by the stud may increase. Moreover, not only the tip <NUM> affects grip and road wear. Particularly, a size of the bottom flange <NUM> affects grip and road wear, too. A large bottom flange <NUM> oftentimes implies that the stud <NUM> is arranged in the stud hole <NUM> in a stiff manner, i.e. the bottom flange <NUM> resists movement of the studs in the negative radial direction -SR when the stud is pressed in this direction. A reason is that the large bottom flange <NUM> supports the stud <NUM> to the rubber material of the tyre beneath the bottom flange in a sturdy manner. This typically results in a high piercing force of the stud on the road; and a high piercing force implies high road wear. This applies also vice versa. A small bottom flange will, in general, reduce the piercing force and in this way the road wear.

The piercing force herein refers to the piercing force as defined in the regulation "Ajoneuvon nastarenkaiden tekniset vaatimukset ja tyyppihyväksyntä" TRAFICOM/<NUM>/<NUM>. <NUM>/<NUM> of the Ministry of Transport and Communications on studs of tyres for vehicles (dated <NUM>. This Ministry is the Ministry of Transport and Communications of Finland.

It has been found that a good compromise between the piercing force and the road wear is achieved when a ratio A140/H110 of the first area A140 to the first height H110 is <NUM> to <NUM><NUM>/mm. An even more preferable value for this ratio A140/H110 is <NUM> to <NUM><NUM>/mm, most preferably <NUM> to <NUM><NUM>/mm.

In accordance with an embodiment of the invention, the shape of all the studs is substantially similar to each other, but some of the measures of the studs are different so that height H110 of the pin <NUM> is longer in at least most of the studs <NUM> in the centre area CR than most of the studs <NUM> in the shoulder areas SR1, SR2. <FIG> illustrates as a side view an example of a stud <NUM> for the centre area CR and <FIG> illustrates as a side view an example of a stud <NUM> for the shoulder areas SR1, SR2. It can be seen that the height H110 of the pin <NUM> of the stud <NUM> of <FIG> is longer than the height H110 of the pin <NUM> of the stud <NUM> of <FIG>.

<FIG> shows a cross section of a part of a tyre <NUM> according to an embodiment of the invention in which the studs 100b of <FIG> have been used in the centre area CR and the studs 100a of <FIG> have been used in the shoulder areas SR1, SR2. It can be seen that the depth of stud holes 250b in the centre area CR and in the shoulder areas SR1, SR2 is substantially equal.

In accordance with an embodiment of the invention, the higher protrusion is achieved by using similar stud lengths in both centre area and shoulder areas but using stud holes having different depths in the centre area than in the shoulder areas. This is illustrated in <FIG>, which shows a cross section of a part of the tyre <NUM>++ according to this embodiment. It can be seen that the depth of the stud holes 250b in the centre area CR is smaller than the depth of the stud holes 250a in the shoulder areas SR1, SR2.

It should be noted that the cross sections of <FIG> are only showing principles of these two embodiments but the scales and all the details of these figures may not correspond to practical implementations. For example, the tread <NUM> is not showing different layers which tyres <NUM> typically have.

In accordance with yet another embodiment of the invention, the higher protrusion is achieved by using in the centre area CR studs which have longer total length H100 than studs in the shoulder area SR1, SR2, but the pin <NUM> of each stud may have substantially equal length H110. Hence, the length H120 (<FIG>) of the body <NUM> of the stud <NUM> is longer in the studs of the centre area than in the studs of the shoulder area SR1, SR2.

Studs <NUM> in the centre area CR tend to wear faster than studs <NUM> in the shoulder areas SR1, SR2. Therefore, having the higher protrusion in the studs <NUM> of the centre area CR may prolong the good grip of the tyre <NUM>. Furthermore, the studs in the shoulder areas SR1, SR2 tend to rise upwards during usage of the tyre <NUM>, wherein the grip in the shoulder areas SR1, SR2 may also tend to last longer. Overall, these two factors may make it possible to use the studder tyres <NUM> according to the invention longer than without utilization of the present inventive idea.

The low value of road wear may be achieved e.g. by having a sufficiently low dynamic impact to the road, particularly when driving at the speed indicated in the road wear standard. Features affecting the dynamic impact of the studs to the road include:.

Both the first area A140 and the rubber material supporting the bottom flange <NUM> have effect on how sturdy the stud is supported to the rubber material of the tire.

As for the material of the tyre <NUM>, also the rubber material of the tread <NUM> may affect road wear induced by the studs <NUM> of the tyre <NUM>. Thus, in an embodiment of the invention, the tread <NUM> comprises rubber material having a Shore hardness in the range <NUM> to <NUM> Sh(A) as measured with durometer type A, at the temperature <NUM>. In an embodiment of the invention, the tread <NUM>, in particular the part of the tyre that is configured to contact a road in use, is formed of rubber material having a Shore hardness in the range <NUM> to <NUM> Sh(A) as measured with durometer type A, at the temperature <NUM>.

The stiffness of the tread blocks <NUM> can also be softened by providing sipes <NUM> to the tread <NUM>. Thus, in an embodiment of the invention, at least some of the tread blocks <NUM> are provided with sipes <NUM>. As is well known, sipes <NUM> are narrow openings in tread blocks <NUM>. Sipes <NUM> are shown in <FIG> and <FIG>. Concerning the narrowness of the sipes, in an embodiment of the invention, a width W240 of all the sipes <NUM> is less than <NUM>. The width W240 of a sipe is shown in <FIG>. In an embodiment of the invention, a depth D240 (<FIG>) of all the sipes <NUM> is at least <NUM>. A bottom a sipe needs not be even. In such a case the depth of the sipe <NUM> refers to a depth of the deepest point of the sipe <NUM>.

The tread blocks <NUM> of the tread <NUM> also limit grooves <NUM>. Thus, the tread <NUM> comprises tread blocks <NUM> such that grooves <NUM> are arranged between the tread blocks <NUM>. As an example, <FIG> shows a groove <NUM> arranged between a first tread block 220a and a second tread block 220b. In an embodiment of the invention, a width W230 of at least one of the grooves <NUM>, as measured on the level of the tread <NUM> limiting the groove <NUM>, is more than <NUM>. The width W230 is shown in <FIG>. The grooves may taper radially inward (i.e. in the -SR direction). Thus, in an embodiment of the invention, a width W230 of at least one of the grooves <NUM> decreases in an inward radial direction -SR of the tyre. Reference is made to <FIG>. In an embodiment of the invention, a depth D230 of at least one of the grooves <NUM> is more than <NUM>, preferably <NUM> to <NUM>. A depth of a sipe <NUM> is less than a depth of a groove <NUM>. More specifically, in an embodiment of the invention, a depth D240 of all the sipes <NUM> is less than a depth D230 of one of the grooves <NUM>.

When the tyre <NUM> comprises sipes, preferably, no sipe <NUM> is provided close to a stud hole <NUM>, in which a stud <NUM> has been installed. Referring to <FIG>, a stud <NUM> has been installed in a stud hole <NUM>, and no part of any of the sipes <NUM> is arranged closer than the distance DSS to a centre of the stud hole <NUM>. The distance DSS may be in a range from <NUM> to <NUM>, for example. Preferably, no part of any of the sipes <NUM> is arranged closer than <NUM> or closer than <NUM> to a centre of the stud hole <NUM>. In addition or alternatively, multiple studs have been installed in multiple stud holes and no part of any of the sipes <NUM> is arranged closer than <NUM>, <NUM>, <NUM>, <NUM> or <NUM> to a centre of any one of the stud holes <NUM>. In addition or alternatively, multiple studs have been installed in multiple stud holes and no part of any of the sipes <NUM> is arranged closer than <NUM> to <NUM> to a centre of any one of the stud holes <NUM>. <FIG> shows the distance DSS that is arranged between a sipe <NUM> and a centre of a stud hole <NUM>. This has the effect that stud <NUM> is reliably fixed to its stud hole <NUM>. Otherwise the sipe <NUM> would soften the tread also near the stud hole <NUM> and in this way increase the risk of the stud <NUM> falling from the stud hole <NUM>. Thus, this also improves the grip of the tyre <NUM>.

In an embodiment of the invention, at least some of the grooves <NUM> are inclined such that they define a V-shape or a half of a V-shape, the V-shape or the half thereof defining a direction of rotation R of the tyre <NUM> when used driving forwards, the direction of rotation R being reverse to the direction to which the V-shape or the half thereof opens. As an example, the grooves of <FIG> define a half of a V-shape. In contrast the grooves of <FIG> define a full V-shape. Such a tread is what is commonly known as "unidirectional" i.e. the tyre is designed to be fitted to the vehicle wheel in one particular way. This improves the grip of the tyre by improving the efficiency of draining water and/or slush from underneath the tyre <NUM> in regular use of the tyre. This arrangement of grooves also does not increase the road wear. Such a unidirectional tyre may comprise a marking on a sidewall of the tyre, the marking being indicative of the direction of rotation for the tyre.

Such a tyre can be manufactured by vulcanizing a green tyre to form the tyre <NUM> and forming stud holes to the tread <NUM> of the tyre <NUM> during the vulcanizing the green tyre. After vulcanization, the studs <NUM> are installed to the stud holes <NUM> of the tread <NUM>. <FIG> shows two stud holes <NUM> to which a stud has not been installed. As shown therein, typically the stud holes <NUM>, before the studs <NUM> have been inserted into the holes <NUM>, are small compared to the studs <NUM>. However, because the tread blocks <NUM> are elastic, the stud holes <NUM> are stretched when installing the studs <NUM> to the holes <NUM>. This further improves fixing of the studs <NUM> to the stud holes <NUM>.

When the tyre comprises sipes <NUM>, in an embodiment of the invention, the sipes are formed to the tread <NUM> of the tyre <NUM> during the vulcanizing the green tyre by using lamella blades.

As detailed above both (i) the area of the cross section of the pin <NUM> and (ii) a stiffness of the support of the bottom flange <NUM> affect the dynamic impact. Thus, as an example, the tyre according to the invention may comprise a stud <NUM> comprising the bottom flange <NUM>, the second part <NUM>, and the pin <NUM> such that the greatest diameter of the bottom flange <NUM> is in the range from <NUM> to <NUM> and the smallest diameter of the bottom flange <NUM> is in the range from <NUM> to <NUM>.

The cross-section of the bottom flange <NUM> is preferably greater than a cross-section of the second part <NUM>. Thus, the bottom flange <NUM> anchors the stud <NUM> well to the stud hole <NUM>. Therefore, in an embodiment of the invention, the second part <NUM> has a third cross-section on a plane that has a normal in the longitudinal direction Sz of the stud <NUM>, the third cross-section having a third area (A130, A132, A134), and the first area A140 is greater than the third area (A130, A132, A134). The third area A130 may correspond to a (sole) third area of the second part; or the third area A130 may correspond to an area A132 of a cross-section of a waist <NUM> or an area A134 of a cross-section of a upper flange <NUM>.

As detailed above, the protrusion P100 of a stud <NUM> affects the dynamic impact. Preferably, the protrusion P100 is between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, and most preferably between <NUM> and <NUM> measured from an inflated unused tyre. The protrusion of stud P100 is shown in <FIG>. In an embodiment of the invention, these values apply to an average of the protrusions P100 of the studs <NUM> (i.e. all the studs <NUM>) of the tyre. In an embodiment of the invention, these values apply to all the protrusions P100 of the studs <NUM> (i.e. all the studs <NUM>) of the tyre individually. However, it should be noted that, due to the inventive idea presented in this specification, the average of protrusions is bigger in the centre area CR than in the shoulder areas SR1, SR2.

In an embodiment of the invention the tyre <NUM> comprises multiple studs <NUM> comprising only pins <NUM> having one type of cross section. Thus, in an embodiment of the invention, the pin <NUM> of all the studs of the tyre <NUM> are identical in shape.

In another embodiment of the invention the tyre <NUM> comprises more than one type of stud pins <NUM>. In other words, some studs have pins of one type of cross section and some other studs have pins of another type of cross section. There may also be a third, fourth etc. types of cross sections of the pins <NUM> at different locations of the studs <NUM> of the tyre <NUM>.

In yet another embodiment of the invention the tyre <NUM> comprises more than one type of studs <NUM>. In other words, some studs have one type of cross section at different locations and some other studs have another type of cross section at those locations. There may also be a third, fourth etc. types of cross sections at different locations of the studs <NUM> of the tyre <NUM>.

To this end, in an embodiment of the invention the tyre <NUM> comprises multiple studs 100a of a first stud type and multiple studs 100b of a second stud type. <FIG> shows a tread <NUM> to which multiple studs 100a of a first stud type and multiple studs 100b of a second stud type have been installed. For example, the shape of the studs 100a of the first type are shown in <FIG>, and the shape of the studs 100b of the second type are shown in <FIG>. Also <FIG> shows a tread <NUM> to which multiple studs 100a of a first stud type and multiple studs 100b of a second stud type have been installed.

In <FIG>, a central region CR of the tread comprises studs 100b of the second stud type, and both a first shoulder region SR1 and a second shoulder region SR2 comprise studs 100a of the first stud type. Studs 100b of the second type are not identical with the studs 100a of the first stud type. Thus, in an embodiment of the invention, a central region CR of the tread <NUM> is arranged between a first shoulder region SR1 of the tread <NUM> and a second shoulder region SR2 of the tread <NUM>. The central region CR comprises a circumferential central line CL of the tread <NUM>. In an embodiment of the invention, the circumferential central line CL of the tread <NUM> divides also the central region to two equally wide parts. The first shoulder region SR1 extends in an axial direction SAX from a first side S1 of the tread <NUM> towards the circumferential central line CL. The first side S1 is shown in <FIG>. The second shoulder region SR2 extends in an axial direction SAX from a second side S2 of the tread <NUM> towards the circumferential central line CL. The second side S2 is also shown in <FIG>. In an embodiment of the invention, the first shoulder region SR1, the second shoulder region SR2 and the central region CR constitute the tread <NUM>. In other words, in the embodiment of the invention, the tread <NUM> consists of the first shoulder region SR1, the second shoulder region SR2 and the central region CR.

In accordance with an embodiment of the invention, the central region CR has a width which is in a range from <NUM> % to <NUM> % of the total width W210 of the tread <NUM>, but may be different from that. Some examples to be mentioned are the range from <NUM> % to <NUM> %, or <NUM> % to <NUM> %.

The tread blocks <NUM> of the tyre <NUM> define a land portion LP of the tread <NUM>. A part of the land portion LP of the tread is shown by black colour in <FIG>. Naturally, the land portion extends around the whole circumference of the tread <NUM>. The land portion of the tread <NUM> consists of the parts of the tread blocks <NUM> that are arranged to contact a surface (e.g. the road) in use of the tyre <NUM>. The land portion has a total land area A220 (as measured e.g. in units of dm<NUM>). Some of the tread blocks <NUM> of the tyre <NUM> have been provided with studs, and also the cross-sections of the studs <NUM> belong to the land portion LP.

An area of the tread <NUM> which is simultaneously contacting a surface may be called as a footprint. The area of the footprint may slightly vary due to certain conditions. For example, the load affected to each tyre and the pressure within the tyres may affect the area of the footprint. The more load the larger may be the area of the footprint. On the other hand, the higher the pressure the smaller the footprint may be.

The tread blocks <NUM> of the tyre <NUM> define an envelope surface. The envelope surface consists of the land portion LP of the tread <NUM> and the regions defined by the openings of the grooves <NUM>. The openings of the grooves <NUM> may be commonly referred to as a sea portion SP of the envelope surface, as shown in black colour in <FIG>. Also the sea portion SP extends around the whole circumference of the tread <NUM>. The sea portion SP of the envelope surface has a sea area A230. The land portion LP (<FIG>) and the sea portion SP (<FIG>) together form the envelope surface. Thus, the tread blocks <NUM> are delimited outward in the radial direction +SR by the envelope surface; and the land portion of the envelope surface forms the ground contact surface of the tread <NUM>. The envelope surface has a total envelope area A210, as measured e.g. in units of dm<NUM>.

Thus, the total envelope area A210 is the sum of the land area A220 and the sea area A230, i.e. A210=A220+A230. Referring to <FIG>, a width of the tread <NUM> is depicted by W210 and a circumference by C210. The total envelope area A210 is thus approximately equal to the product W210×C210. However, because the tread <NUM> is also curved in the axial direction SAX on the tyre <NUM>, this is only an approximation. As for the circumference C210, the circumference C210 may equal pi (i.e. <NUM>) times the overall diameter indicated in Table <NUM>.

In this description, an average land ratio refers to the ratio of the total land area A220 to the total envelope area A210. In other words, by the land ratio is meant the ratio of the ground contacting surface area of tread blocks to the imaginary ground contacting area of the tread, the imaginary ground contacting area of the tread including spaces (i.e. grooves) between adjacent blocks and the blocks themselves. In other words, by the land ratio is meant the ratio of the ground contacting surface area of tread blocks to a ground contacting area of an imaginary tread, the imaginary tread having been formed from the tread by filling the grooves with tread material.

In the art, one sometimes uses the term sea area ratio to mean the ratio of the sea area to the imaginary ground contacting area of the tread. In line with these definitions the sum of the land ratio and the sea area ratio equals one.

In the art, the term "land-to-sea ratio" may, occasionally, be used interchangeably with the land ratio as defined above. However, the term land-to-sea ratio or land/sea ratio may relate to a ratio of the land area (ground contacting area) to the sea area (non-contacting area) of the tread. To avoid possible confusion, the term land area is used throughout this description and in the meaning defined above.

According to an embodiment of the invention, the land ratio of the tread is greater in a central area than in a shoulder area. <FIG> therefore show a circumferential central line CL of the tread <NUM>. The circumferential central line CL divides the tread <NUM> to two equally wide parts. The circumferential central line CL is an intersection of the tread <NUM> and its equatorial plane EP. As shown in <FIG>, a central region CR of the tread <NUM> is arranged between a first shoulder region SR1 of the tread <NUM> and a second shoulder region SR2 of the tread <NUM>. The central region CR comprises the circumferential central line CL of the tread <NUM>. In an embodiment of the invention, the circumferential central line CL of the tread <NUM> divides also the central region to two equally wide parts. Limits between these regions are shown by dash lines in <FIG>. The circumferential central line CL is also shown by a dash line. In an embodiment of the invention, the first shoulder region SR1, the second shoulder region SR2 and the central region CR constitute the tread <NUM>. In other words, in the embodiment of the invention, the tread <NUM> consists of the first shoulder region SR1, the second shoulder region SR2 and the central region CR.

In an embodiment of the invention, at least two thirds of the studs <NUM> that are arranged in the central region CR are of the second stud type (they are studs 100b), and at least two third of the studs arranged in the first and second shoulder regions SR1, SR2 are of the first stud type (they are studs 100a).

In an embodiment of the invention, the studs 100a of the first stud type comprise substantially identical first pins. A cross-section of a first pin, the plane of the cross-section having a normal to the longitudinal direction Sz of the stud, has a first shape. Moreover, the studs 100b of the second stud type comprise substantially identical second pins. A cross-section of a second pin, the plane of the cross-section having a normal to the longitudinal direction Sz of the stud, has a second shape. The second shape is different from the first shape. For example, the pin <NUM> of the stud 100a of the first type is shown in <FIG>, and the pin <NUM> of the stud 100b of the second type, is shown in <FIG>.

In an embodiment of the invention, not only the stud pins <NUM> of the first stud type are different from the stud pins of the second type, but also at least some parts of the body <NUM> of the studs 100a of the first stud type are different from corresponding parts of the body <NUM> of the studs 100b of the second stud type.

By using at least two different types of studs, the grip of the tyre can be optimized. This is particularly true, when studs of the second type are used in the central region CR, and studs of the first type are used in the shoulder regions SR1, SR2.

The grip of the tyre can be improved by using sufficiently many studs. The grip of the tyre can be improved by using sufficiently many studs on both sides of the circumferential central line CL.

Concerning the former, in an embodiment of the invention, the tread <NUM> has the first width W210 and the first circumference C210, as defined above. Moreover, the tread <NUM> is provided with a total number N100 of studs <NUM>. A ratio (N100/(W210×CL)) of the total number of the studs N100 to the width of the tread W210 and the circumference C210 of the tread can be equal to or more than <NUM> pieces per square-decimetre (pcs/dm2). In an embodiment of the invention, the ratio (N100/(W210×C210)) of the total number N100 of the studs to the product W210×C210 of the first width W210 and the first circumference C210 is more than <NUM> pieces per square-decimetre (pcs/dm<NUM>).

In another embodiment of the invention, a ratio (N100/(W210×C210)) of the total number N100 of the studs to the product W210×C210 of the first width W210 and the first circumference C210 is more than <NUM> pieces per square-decimetre (pcs/dm<NUM>). The first circumference C210 may be measured along the circumferential central line CL, e.g. along a circumferential central line of the envelope surface of the tread <NUM>.

Thus, in an embodiment of the invention, N100/(W210×C210CL) ≥ <NUM> pcs/dm<NUM>, wherein N100 is a total number of studs in the tire, W210 is the width of the tread (dm), and C210 is the circumference of the tyre <NUM> in dm, measured along the circumferential central line CL.

In the other embodiment of the invention mentioned above, N100/(W210×C210CL) > <NUM> pcs/dm<NUM>.

In the third embodiment of the invention mentioned above, N100/(W210×C210CL) > <NUM> pcs/dm<NUM>.

Concerning the latter (the number of studs on each half of the tread), in an embodiment of the invention, the circumferential central line CL of the tread <NUM> (as well as the equatorial plane EP) defines a first half of the tread <NUM> and a second half of the tread <NUM> (see <FIG>). In the embodiment of the invention, the first half comprises a first number N1 of studs <NUM>, 100a, 100b and the second half comprises a second number N2 of studs <NUM>, 100a, 100b such that a ratio (N1/N2) of the first number to the second number is <NUM> % to <NUM> %.

The width W210 of the tread <NUM> may be somewhat smaller than a width W200 of the tyre. Within this description, the width W200 of the tyre <NUM>, as shown in <FIG>, refers to the "Section Width" as defined in the ETRTO standards manual <NUM>. The height H200 of the tyre <NUM> is also shown in <FIG>, and is defined as the "Section Height" in the ETRTO standards manual <NUM>. Correspondingly, the Section Width, i.e. the width W200 of the tyre <NUM> as defined herein (and in the ETRTO standards manual) is the linear distance between the outsides of the sidewalls of an inflated tyre excluding elevations doe to labelling (markings), decoration, or protective bands or ribs. <FIG> also shows half of a cross section of a rim <NUM> onto which the tyre <NUM> has been installed. As for the circumference C210, the circumference C210 may equal pi (i.e. <NUM>) times the overall diameter indicated in Table <NUM> (see above).

The first width W210 (i.e. that of the tread) may be equal to the reference tread width as defined in the ETRTO standards manual <NUM> (see Design Guide, Page PC. In accordance with the definitions therein, the reference tread width C is calculatable as<MAT>.

Herein s is the Section Width (defined above), i.e. the width W200 of the tyre, and ar is the nominal aspect ratio, which is readable from the size marking w/hRr (see above), the "h" indicating the aspect ratio. Thus, the first width W210 of the tread <NUM> may equal the value C as calculatable with the equation given above, wherein s equals W200.

The following Table <NUM> shows some examples of measures of tyres. The size indicates the diameter and width of the tyre, the aspect ratio indicates the height of the tyre as a percentage of the width of the tyre, ETRTO design width is the width of the tyre according to ETRTO, the reference tread width is the actual width of the tread.

Referring to <FIG>, each stud is arranged at a distance from the circumferential central line CL. Thus, each stud defines a circumferential row rij, the circumferential row being parallel to the circumferential central line CL and at such a distance that the stud is arranged on the circumferential row rij. Herein "rij" stands for j:th circumferential row in the i:th half. Fig 4c shows nine rows (j=<NUM>, <NUM>,. , <NUM>) on both halves (i=<NUM> or <NUM>). Several studs may be arranged on the same circumferential row. However, preferably not all the studs of first half of the tread are arranged on the same circumferential row. This applies also for the studs of the second half of the tread. Preferably, studs are arranged on at least six different circumferential rows.

Referring to <FIG>, in an embodiment of the invention, each one of the multiple studs <NUM>, 100a, 100b of the tyre <NUM> is arranged on a circumferential row (r11, r12, r13, r14, r15, r16, r17, r18, r19, r21, r22, r23, r24, r25, r26, r27, r28, r29) such that the studs <NUM>, 100a, 100b are arranged on at least six different circumferential rows. Different circumferential rows (r11, r12, r13, r14, r15, r16, r17, r18, r19, r21, r22, r23, r24, r25, r26, r27, r28, r29) are arranged a distance apart from each other, and multiple studs may be arranged on only one circumferential row (r11, r12, r13, r14, r15, r16, r17, r18, r19, r21, r22, r23, r24, r25, r26, r27, r28, r29).

Preferably, the circumferential central line CL of the tread <NUM> defines the first half of the tread <NUM> and the second half of the tread <NUM>, and the studs are arranged such that at least three different circumferential rows (r11, r12, r13, r14, r15, r16, r17, r18, r19) of the at least six different circumferential rows (r11, r12, r13, r14, r15, r16, r17, r18, r19, r21, r22, r23, r24, r25, r26, r27, r28, r29) are arranged on the first half, and at least three different circumferential rows (r21, r22, r23, r24, r25, r26, r27, r28, r29) of the at least six different circumferential rows (r11, r12, r13, r14, r15, r16, r17, r18, r19, r21, r22, r23, r24, r25, r26, r27, r28, r29) are arranged on the second half.

Having such many rows rij effective spreads the studs to the tread <NUM> reasonably evenly, thereby improving the grip.

In addition to the tread <NUM> of the tyre <NUM>, the structure of the tyre <NUM> provides for sufficient stiffness of the tyre <NUM> and thereby also affect the grip and road wear properties of the tyre <NUM>. The tread <NUM> is provided as an outermost layer of a carcass of the studded tyre <NUM>. A quarter of a cross-section of a tyre <NUM> is shown in <FIG>. The relevant cross-section for Fig. 5e is such a cross-section that is a cross-section of the tyre <NUM> with a plane that comprises the axis of rotation of the tyre, which is parallel to the axial direction SAX (see <FIG>) and located in the centre defined by the tyre <NUM>. Such cross-section has two parts, which are substantially identical. One of such parts is shown in <FIG>. A half of only one of the parts is shown in <FIG>. An equatorial plane EP (shown in <FIG>) of the tyre <NUM> divides the tyre to two equally large parts. The circumferential central line CL defined above is arranged in the equatorial plane EP.

As detailed above, the tyre comprises the tread blocks <NUM> that define the grooves <NUM> and the tread <NUM>, which is an outermost layer of the carcass. Preferably, the carcass of the studded tyre <NUM> comprises one or more layers of reinforcing textile or textiles and one of more reinforcing metal layers.

In general, a tyre <NUM> has side surfaces on opposite sides of the tread <NUM>. The side surfaces connect the bead area of the tyre to the tread <NUM>. The side surfaces may have various markings indicating the tire size, tire speed class, tire purpose (winter/summer), tire manufacturer and/or tire name. The bead area of a tyre has a cable. The function of the cable and the bead area is to fit the tire <NUM> to the rim.

The tyre <NUM>, in particular the carcass thereof, comprises a first ply <NUM>. The ply/plies <NUM> may comprise fibrous material, e.g. Kevlar, polyamide, carbon fibres, polyester or glass fibres. In an embodiment of the invention, the tire further comprises a second ply. In this embodiment, the second ply may also comprise fibrous material.

The carcass further comprises a first metal belt <NUM>. Preferably, the carcass further comprises a textile belt <NUM>, such as a textile belt <NUM> comprising fibrous polyamide (e.g. Nylon, aramid, or Cordura). Preferably, the carcass further comprises the second ply and a second metal belt <NUM>. The metal belt(s) <NUM>, <NUM> is/are resilient metal belts, such as steel belts comprising wires.

The tread blocks <NUM> are formed in a cap layer <NUM> of the tyre <NUM>. The cap layer <NUM> may further comprise material connecting the tread blocks <NUM> to the cap layer <NUM> and layers beneath the cap layer <NUM>. Under the tread blocks <NUM> of the tread <NUM>, i.e. under the cap layer <NUM>, the tyre preferably comprises an underlayer <NUM> made of suitable rubber material. A purpose of the underlayer <NUM> is to adaptively affect the impact of the studs to the road according to temperature. Thus, at higher temperatures (e.g. above <NUM>) the impact of the studs may be lower than at lower temperatures, e.g. below <NUM>.

Hence, road wear due to the studs <NUM> of the tyre <NUM> may be lower when roads are not covered by show and/or ice. Thus, in an embodiment of the invention, the bottom flange <NUM> of at least a part of the studs <NUM> of the tyre <NUM> are arranged partly in the underlayer <NUM>.

The underlayer <NUM> may have a hardness which may vary substantially with the ambient temperature, wherein the wear of the road surface may be reduced. The underlayer <NUM> is preferably arranged at least partly below the anti-skid stud. Thus, the bottom of the anti-skid stud can be in contact with the underlayer <NUM>, and the anti-skid stud can be pressed against and/or retract into the underlayer <NUM>.

The anti-skid stud <NUM>, preferably the bottom flange <NUM> of the anti-skid stud, can be in direct contact with the underlayer <NUM>. Thus, in this embodiment of the invention, there is no other material layer between the anti-skid stud <NUM> and the underlayer <NUM>. Alternatively, for example, a separate stud pad <NUM> may be arranged between the anti-skid stud <NUM> and the underlayer <NUM>.

Further, the studded tyre <NUM> may comprise a separate bottom rubber ply (also called as an undertread) arranged below the underlayer <NUM>. Thus, the properties of the studded tyre <NUM> can be improved. Moreover, the process of manufacture of the tyre <NUM> can be easier to control. In an example, the studded tyre <NUM> is not provided with a bottom rubber ply below the underlayer <NUM>. Thus, the manufacturing costs of the tyre <NUM> can be reduced.

As depicted in <FIG>, preferably the studs <NUM> are arranged to contact the underlayer <NUM> directly or via stud pads <NUM>. The stud holes <NUM> may e.g. penetrate into the underlayer <NUM> through the tread cap layer <NUM> and, optionally, through an intermediate layer <NUM>. As an example, in <FIG>, a stud hole (and the stud <NUM>) penetrates into the underlayer <NUM> through the tread cap layer <NUM>. As an example, in <FIG>, a stud hole (and the stud <NUM>) penetrates into the underlayer <NUM> through the tread cap layer <NUM> and an intermediate layer <NUM>. As indicated in <FIG>, a stud pad <NUM> may be arranged in between the underlayer <NUM> and the bottom flange <NUM> of the stud <NUM>. The bottom flange <NUM> of at least a part of the studs <NUM> of the tyre <NUM> are arranged at least partly on the underlayer <NUM>.

<FIG> illustrates an example in which the bottom flange <NUM> and a part of the waist <NUM> are embedded in the underlayer <NUM> in a tyre which does not have the intermediate layer <NUM>. <FIG> illustrates an example in which the bottom flange <NUM> and a part of the waist <NUM> are embedded in the underlayer <NUM> in a tyre which has the intermediate layer <NUM> above the underlayer <NUM>. In this example the intermediate layer <NUM> and also a part of the underlayer <NUM> surrounds the waist <NUM> but the intermediate layer <NUM> can also be higher at the height of the upper flange <NUM>, for example.

<FIG> shows a detailed view of the cap layer (as indicated by the tread block <NUM>) and a underlayer <NUM>. As detailed therein, the bottom flange <NUM> is in contact with the underlayer <NUM>. Therefore, the material of the underlayer <NUM>, in connection with the first area A140 define a degree of support the carcass of the tyre <NUM> imposes on the stud <NUM>. Support is needed particularly at low temperatures so that the protrusion of studs <NUM> from the surface of the treads <NUM> will not become too low when the studs are in contact with the road surface. At temperatures when no ice or snow should not exist on the road surface the adaptive underlayer becomes softer wherein the protrusion of studs <NUM> from the surface of the treads <NUM> may become lower and thus may wear road surface less than if the underlayer <NUM> were not adaptive. A reasonably soft material of the cap layer and the treads provides for good grip on ice and snow.

For these reasons, in an embodiment of the invention, at an ambient temperature of -<NUM> a Shore (A) hardness of the underlayer <NUM> is not less than a Shore (A) hardness of the material of the tread blocks <NUM>. The mechanical properties of the underlayer <NUM> need not depend on temperature; whereby this difference in the Shore hardnesses may apply also at higher temperatures.

However, preferably, the material of the underlayer <NUM>, which supports the bottom flange <NUM>, is selected such that it softens at higher temperatures. In other words, the hardness of the material of the underlayer <NUM> under each stud <NUM> decreases when temperature of the material increases (i.e. the hardness has a negative temperature coefficient). This has the effect that even if the studs are highly supported at low temperatures (because of the shore hardness, see above), at higher temperatures the studs do not wear the road as much, because of the reduced support provided by the softer underlayer <NUM>.

Therefore, in an embodiment of the invention, the underlayer <NUM> comprises adaptive material. The adaptive material is adaptive to the temperature in the sense that it hardens at low temperatures and softens at high temperatures. Thus, the underlayer according to this specification can also be called as an adaptive underlayer. The underlayer may consist primarily or entirely of the adaptive material layer. The adaptive material layer comprises a material having a hardness substantially depending on ambient temperature.

The adaptive material layer can be made of a material compound having a hardness substantially depending on ambient temperature. Preferably, the underlayer is made of an elastomer material having a hardness depending on the temperature of the elastomer material.

The materials for the underlayer and the intermediate layer can be selected so that a dynamic stiffness of the underlayer differs from a dynamic stiffness of the intermediate layer at most temperatures.

The dynamic stiffness of the underlayer, determined at a temperature of <NUM>, can be configured to be less than <NUM> MPa, preferably from <NUM> to <NUM> MPa. Further, the dynamic stiffness of the intermediate layer, determined at a temperature of <NUM>, can be configured to be at least <NUM> MPa, preferably at least <NUM> MPa, and more preferably from <NUM> to <NUM> MPa. Technical effect is to decrease road wear while the intermediate layer supports the whole tire and the studs of the tire at the warmer temperature.

The dynamic stiffness of the underlayer, determined at a temperature of <NUM>, can be configured to be at least two times the dynamic stiffness of the underlayer at a temperature of <NUM>. Further, the dynamic stiffness of the intermediate layer, determined at a temperature of <NUM>, can be configured to be from <NUM> to <NUM> times, preferably from <NUM> to <NUM> times, the dynamic stiffness of the intermediate layer at a temperature of <NUM>. Technical effect is that the winter grip properties of the winter tire can be substantially improved while the intermediate layer supports the whole tire and the studs of the tire at warmer temperatures.

The dynamic stiffness of the underlayer can be at least <NUM>% higher, preferably at least <NUM>% higher than the dynamic stiffness of the intermediate layer at a temperature of <NUM>. Technical effect is that the ice grip properties of the winter tire can be substantially improved at <NUM>. The dynamic stiffness of the underlayer may further be equal to or less than <NUM> % higher, such as equal to or less than <NUM>% higher, preferably equal to or less than <NUM>% higher than the dynamic stiffness of the intermediate layer at a temperature of <NUM>.

Furthermore, the dynamic stiffness of the intermediate layer can be higher than the dynamic stiffness of the underlayer at a temperature of at least <NUM>, such as at a temperature of at least <NUM>. In a particularly advantageous embodiments of the invention, the dynamic stiffness of the intermediate layer is higher than the dynamic stiffness of the underlayer at temperatures from <NUM> to <NUM>. Technical effect is to reduce road wear while improving handling properties of the tire. Further technical effect is that the intermediate layer effectively supports the stud.

The dynamic stiffness of the underlayer at -<NUM> can be at least <NUM> times the dynamic stiffness of the underlayer at +<NUM>. Thus, the grip properties of the winter tire can be substantially improved, and, for example, the braking distance needed by the winter tire under certain conditions can be substantially reduced.

The dynamic stiffness E* of the underlayer <NUM> can be.

The change in the dynamic stiffness of the underlayer upon a decrease in the temperature can have a greater impact on the grip of the tire in winter than the change in the hardness of the material upon a decrease in the temperature. For the above-mentioned dynamic stiffness values, the adjustment of the stud's dynamic impact of the tire at different temperatures can be more controllable, and the grip properties of the winter tire can be better optimized for different temperatures. Thanks to the above-mentioned dynamic stiffness, for example the braking distance on an icy road can be substantially reduced.

In a preferred example, for optimizing the grip properties of the tire in winter,.

In general, the higher the dynamic stiffness E*, the harder the material. These values have been found suitable for providing sufficient grip at low temperatures, yet low road wear at high temperatures. In this specification, the term dynamic stiffness E* refers to the stiffness of the material as determined according to the standard ASTM D5992-<NUM> (reapproved <NUM>).

The temperature dependence of dynamic stiffness E* can be affected by selecting the tan delta peak temperature of the material in a suitable manner. The underlayer <NUM> can comprise, primarily comprise, or consist of a material whose tan delta peak temperature can be at least -<NUM>, for example at least -<NUM>, preferably at least -<NUM>, more preferably at least -<NUM>, or at least - <NUM>, and most preferably at least -<NUM>. Furthermore, the tan delta peak temperature of said material may not be higher than <NUM>, for example not higher than <NUM>, preferably not higher than <NUM>, more preferably not higher than <NUM>, or not higher than <NUM>, and most preferably not higher than <NUM>. Thus, the hardening of the underlayer can be suitable in view of road wear and winter grip. The closer to <NUM> the tan delta peak temperature of the material is arranged, the more accurately the hardening of the underlayer can take place at a point optimal in view of road wear and winter grip, and the easier the impact of the stud can be to control at different temperatures.

Therefore, in an embodiment of the invention, the underlayer <NUM> is made of a material having a tan delta peak temperature that is between -<NUM> and +<NUM>, and more preferably between -<NUM> and +<NUM>.

The term "tan delta" refers to tan δ and the term "tan delta peak" refers to the temperature associated to the turning point of tan delta curve and tan delta maximum value.

The dynamic stiffness E* also affects the hardness of the material. In an embodiment of the invention, a Shore A hardness of the underlayer <NUM> can be configured to be in a range between <NUM> ShA and <NUM> ShA at an ambient temperature of +<NUM>, more preferably at least <NUM> ShA, at <NUM>, and at least <NUM> ShA at an ambient temperature of -<NUM>. More preferably, a Shore A hardness of the underlayer <NUM> is between <NUM> ShA and <NUM> ShA, most preferably in a range between <NUM> ShA and <NUM> ShA at an ambient temperature of +<NUM>, and higher than <NUM> ShA at an ambient temperature of -<NUM>.

Furthermore, the dynamic stiffness of the underlayer can be lower than <NUM> MPa at an ambient temperature of <NUM>, between <NUM> and <NUM> MPa at an ambient temperature of <NUM>, and at least <NUM> MPa at an ambient temperature of -<NUM>.

In this specification, the term Dynamic stiffness (E*) refers to the stiffness of the material which can be determined according to the standard ASTM D5992-<NUM> (reapproved <NUM>).

The mechanical properties as well as their temperature dependence can be adapted by material selections.

The underlayer can comprise one or more polymer materials having a hardness depending on the temperature of the respective polymer material. The underlayer can comprise elastomer material.

In addition to the material of the underlayer <NUM> as such, also the thickness thereof affects the support of the stud <NUM>.

Advantageously, the thermally adaptive underlayer has a thickness in a direction Sz substantially perpendicular to the direction of rotation of the tyre, wherein the thickness d1 is in the range of <NUM> to <NUM>, preferably in the range of <NUM> to <NUM>, most preferably in the range of <NUM> to <NUM>. Thus, the properties of the underlayer can be easier to control so that the underlayer can yield to a particularly suitable extent when the ambient temperature rises, which can further reduce wear of the road surface. In this application, the thickness of the underlayer refers to the thickness of the underlayer when the anti-skid stud is in a rest position, that is, when the anti-skid stud is not subjected to external forces, such as pressure caused by the driving surface.

Referring to <FIG>, the material layer that is adjacent to the underlayer <NUM> and radially inward from underlayer may be the layer <NUM>, i.e. a textile belt. This thickness applies particularly to the thickness of the adaptive material.

Other features of the stud <NUM> that are particularly related to the amount of road wear include the following, each one separately or in combination:
Preferably, a total length of the stud <NUM> is more than <NUM>, advantageously in the range from <NUM> to <NUM>.

In accordance with an embodiment of the invention, the density of the studs <NUM> in the tread <NUM> is more than or equal to <NUM> studs / dm<NUM>, preferably more than <NUM> studs / dm<NUM>, and more preferably more than <NUM> studs / dm<NUM>.

In accordance with an embodiment of the invention, the studs are arranged in three or more rows in the direction of rotation at both sides of the centre line CL. In other words, there are at least six rows of studs.

In accordance with an embodiment of the invention, the number of studs <NUM> on each side of the tyre <NUM> is the same or a difference of the number of studs <NUM> on each side of the tyre <NUM> is not higher than <NUM>%.

In accordance with an embodiment of the invention, there is a lamella-free area around each stud <NUM> so that the radius of the lamella-free area is more than <NUM>, preferably about <NUM>. In accordance with an embodiment of the invention, the radius is about <NUM>.

In accordance with an embodiment of the invention, the studs <NUM> of the tyre <NUM> have one, two or three axes of symmetry.

In addition to the above mentioned properties related to the studs, properties of the tyre <NUM> may also affect the noise generated by the tyre <NUM> during driving.

In accordance with an embodiment of the invention, there is a base layer beneath the studs <NUM>. The base layer may also be called as an underlayer <NUM>.

In accordance with an embodiment of the invention, there is a layer of material under each stud <NUM> which is softer than the intermediate layer at least when the temperature of the tyre is higher than <NUM>.

In accordance with an embodiment of the invention, there is an intermediate layer <NUM> around each stud <NUM>.

In accordance with an embodiment of the invention, there is a stud pad <NUM> under each stud <NUM>.

In accordance with an embodiment of the invention, the tyre <NUM> comprises one kind of studs <NUM>.

In accordance with an embodiment of the invention, the tyre <NUM> comprises at least two different kinds of studs <NUM>.

In accordance with an embodiment of the invention, the tread blocks <NUM> are arranged to groups of over <NUM> pitch on both sides of the tread <NUM>.

In accordance with an embodiment of the invention, stud holes <NUM> have been formed to the tread during vulcanization of the tyre <NUM>.

Claim 1:
A tyre (<NUM>) comprising
- a tread (<NUM>) having tread blocks (<NUM>);
- a plurality of stud holes (<NUM>, 250a, 250b); and
- a plurality of studs (<NUM>) installed in at least some of the stud holes (<NUM>),
characterized in that
- studs (100b) in a centre area (CR) of the tyre (<NUM>) have higher protrusion from a surface of the tread blocks (<NUM>) than studs (100a) in a shoulder area (SR1, SR2) of the tyre (<NUM>).