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 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, studded tyres cause more road wear and noise than tyres without studs.

Reduced noise is beneficial from environmental and well-being points of view. Reduced noise would make driving and travelling in a vehicle less annoying and might improve comfort for the driver and passengers. Reduced noise would not only improve comfort of people in the vehicle but also people outside the vehicle. For example, in cities where traffic is large and where a lot of people live, reduced noise would improve the quality of life. Reduced noise induced by a studded tyre is therefore an important issue of a studded tyre. Naturally, also grip and handling are important characteristics of a studded tyre. A good studded tyre may be an optimal compromise between these features.

The patent application <CIT> discloses a studdable tire capable of remarkably improving an on-ice performance of a studded tire configured by inserting studs into the studdable tire. Holes for inserting studs are arranged in blocks constituting the block array so that the holes within the tire contact area of the tread do not overlap with each other in the tread circumferential direction.

The patent application <CIT> discloses a studded tire, which includes stud pins embedded in a road contact surface of a tread portion.

The patent application <CIT> discloses a spike tyre provided with more than one layer of carcass layer and double breaker layer, while a block lug of predetermined shape is formed on the surface of a tread and many spikes are buried such that the peaks will project through the surface. In such a tyre, a fiber layer is arranged between the spike and the breaker layer.

The utility model application <CIT> discloses a studded tire in which studs are arranged in arrays of 3x3, 4x4 or 5x5 so that in the arrays the studs are in different rows and different columns.

The patent application <CIT> discloses a stud, which is configured to be inserted into a tread portion of a tire. The stud includes a tip end and a base including a flanged bottom portion provided on an end opposite the tip end and extending radially outward, a stump portion provided between the bottom portion and the tip end. The stump portion has a polygonal shape consisting of three concave sides, two convex sides, and one planar side.

The patent application <CIT> discloses a spike for a running surface of a motor vehicle tire. In order to be enabled to accept even greater forces from below, the spike root and the upper part of the spike are twisted in relation to each other, so that the longitudinal axis of the upper part of the spike encloses an angle varying from zero with the longitudinal axis of the spike root.

The patent Cited reference <CIT> discloses a vehicle tire comprising a tire carcass and on top of this a cap consisting of at least one rubber quality and forming the tread. The cap has anti-skid stud holes extending from the tread to its inside.

The patent application <CIT> relates to the automotive industry. The tire contains a tread having a rolling surface, and a set of spikes fixed in the tread and protruding from the rolling surface, while the average surface density of the spikes on the rolling surface is at least <NUM> spikes per dm<NUM>, and the height the protrusion of each spike of the set of spikes is from <NUM> to <NUM>.

An aim of the present invention is to provide a studded tyre which produces less noise than prior art tyres and still provides for good grip.

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 a constellation of the studs is such that less than two studs are in a line perpendicular to a rolling direction of the tyre, that within an area of a footprint less than two studs are in the same line parallel to the rolling direction, and that a distance between two adjacent studs is more than <NUM>.

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, the configuration of the studs is such that the location of studs on one side from a centre line of the tyre differ at least <NUM> and less than or equal to <NUM> from the location of studs on another side of the centre line in the direction of rotation.

Such a tyre can be manufactured by vulcanizing a green tyre to form the tyre and forming stud holes to the tread of the tyre <NUM> during the vulcanizing the green tyre so that all the studs can be installed in a different radial location.

Several embodiments 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> need 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 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.

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>.

According to a first aspect of the invention, there is provided a studded tyre <NUM>, which produces less noise than prior art studded tyres.

<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> being joined to the bottom flange <NUM> and extending 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>.

To provide a good grip, the pin <NUM> should protrude from second part <NUM> sufficiently. A first height H110 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>). 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.

According to an aspect of the invention, a studded tyre has such properties that the tyre, in use, causes only low noise. Such properties include e.g. the constellation of the studs, a dynamic impact of the studs to the road, a number of the studs and the rubber material to which the studs are installed. The term constellation refers to the mutual positioning of studs in the tread <NUM>. Also the terms arrangement configuration of the studs and configuration of the studs may be used to describe how the studs <NUM> are positioned in the tread <NUM> with respect to each other.

According to an embodiment, a tyre <NUM> comprises a tread <NUM> and multiple studs <NUM> in the tread <NUM>. The studs <NUM> comprise pins <NUM> of hard metal or ceramic. What has been said above about the hardness of the pin applies. The studs <NUM> are arranged to the tread <NUM> such that at least the pins <NUM> of the studs <NUM> are exposed on the tread <NUM>. The tyre <NUM>, in particular the constellation of the studs <NUM> thereof, are configured such that noise induced by the tyre <NUM> during driving is particularly low compared to prior art tyres.

The low value of noise may be achieved e.g. by having only one stud impacting the road at the same time. Another feature which may affect the noise is that the studs have sufficiently low dynamic impact to the road. Features affecting the dynamic impact of the studs to the road include:.

When a vehicle having studded tyres is running on a road, studs become in contact with a surface of the road i.e. the studs hit the surface of the road. This causes deformation to the surface structure of the tyre to occur which then is further propagating in the structure of the tyre having a wave form. As this propagating deformation wave meets the interface between the tyre and the structure of the vehicle, it from there on travels in the structure of the vehicle finally reaching the driving compartment of the vehicle and can be audibly sensed, by the operator of the vehicle, as noise. According to the present invention the purpose of the relative positioning of individual studs is to have deformation waves from different studs to not amplify each other but rather compensate each other at least partially. This may be achieved by positioning the studs so that only one stud hits the surface of the road at a time and that when a next stud hits the surface of the road the deformation wave generated by that stud has a different phase compared to the deformation wave generated by the previous stud. Studs which are not within the footprint area do not typically produce any noise so it is sufficient to concentrate the area of the footprint.

<FIG> shows a part of a tread of the tyre <NUM> according to an embodiment and <FIG> illustrates a footprint of a tyre <NUM>. In this example the studs <NUM> are located on the tread so that there are no more than one stud <NUM> (i.e. less than two studs <NUM>) in a direction perpendicular to the direction of rotation R. This direction, which may also be called as an axial direction, is indicated with SAX in <FIG> and with the line <NUM> in <FIG>. Furthermore, in a preferable embodiment, the studs <NUM> are arranged in the tyre <NUM> so that there is only one stud <NUM> in a line in the direction of rotation R within an area of a footprint <NUM> (see <FIG>) at certain conditions. it should be noted that the actual area of the footprint <NUM> of the tyre <NUM> depends on several conditions such as pressure of the tyre <NUM>, load affected on the tyre <NUM>, a diameter of the tyre, and temperature of the tyre. The load depends inter alia on weight of a vehicle to which the tyre <NUM> has been installed. In this specification it is assumed that the pressure of the tyre <NUM> has been set to correspond with recommendations by a manufacturer of the vehicle and/or the tyre <NUM>. The line <NUM> also illustrates a width of the footprint and the line <NUM> illustrates a length of the footprint in an example situation. For example, the footprint of a tyre of the size <NUM>/55R16 is about <NUM> ±<NUM>-<NUM> long and about <NUM> ±<NUM>-<NUM> wide when the pressure of the tyre corresponds a recommended pressure for that tyre and the temperature is within normal use conditions.

In accordance with an embodiment the configuration of the studs is such that studs on one side from the centre line CL of the tyre <NUM> differ at least <NUM> in the direction of rotation from studs on the other side of the centre line CL and is less than or equal to <NUM>. Advantageously, this difference (<NUM> in <FIG>) is in the range from <NUM> to <NUM>.

In accordance with an embodiment the configuration of the studs on one side (a first side, e.g. the left side) from the centre line CL is a mirror image of the configuration of the studs on the other side (a second side, e.g. the right side), but so that no stud on the first side is in the same line <NUM> perpendicular to the direction of rotation R than any of the studs on the second side. In accordance with an embodiment, the arrangement of the studs is such that the orientation of the studs on the left side is a mirror image from the orientation of the studs on the right side but slightly in offset in the direction of rotation. The centre line CL is one example of the mirroring plane but there may also be another mirroring plane or planes.

Moreover, a distance between any two adjacent studs is not less than <NUM>.

As for the material of the tyre <NUM>, also the rubber material of the tread <NUM> may affect noise induced by the studs <NUM> of the tyre <NUM>. Thus, in an embodiment, 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, 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 reduced by providing sipes <NUM> to the tread <NUM>. Thus, in an embodiment, 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, 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, a depth D240 (<FIG>) of all the sipes <NUM> is at least <NUM>. A bottom of 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, 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, 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, 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, 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 <NUM> to a centre of the stud hole <NUM>. 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>. <FIG> shows the distance DSS that is arranged between a sipe <NUM> and a centre of a stud hole <NUM>. The distance DSS may be e.g. at least <NUM>, at least <NUM>, at least <NUM>, at least <NUM> or at least <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, 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, 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 sturdiness 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, 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 the upper flange <NUM>. <FIG> shows a cross-section Id of the upper flange <NUM> of the stud of <FIG> shows a cross-section Ie of the waist <NUM> of the stud of <FIG> shows a cross-section If of the bottom flange <NUM> of the stud of <FIG>.

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, 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, these values apply to all the protrusions P100 of the studs <NUM> (i.e. all the studs <NUM>) of the tyre individually.

In an embodiment the tyre <NUM> comprises multiple studs 100a of a first stud type only. Thus, in an embodiment, all the studs of the tyre <NUM> are identical in shape.

To this end, in an embodiment 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 and the upper flange <NUM> of the first type are shown in <FIG>, and the shape of the studs 100b and the upper flange <NUM> 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, 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, 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, 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, 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, the central region CR has a width which is in a range from <NUM> % to <NUM> % of the total width of the tread <NUM>, but may be different from that, such as from <NUM> % to <NUM> % or from <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, 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, 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, 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, the tread <NUM> consists of the first shoulder region SR1, the second shoulder region SR2 and the central region CR.

In an embodiment, 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 thirds of the studs that are arranged in the first and second shoulder regions SR1, SR2 are of the first stud type (they are studs 100a).

In an embodiment, 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, 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 properties 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, 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, 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, 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>). 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, 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 mentioned above, N100/(W210×C210CL) > <NUM> pcs/dm<NUM>.

In the third embodiment 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, 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, 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> 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, 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, 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, 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, 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 in 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 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, 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, 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, 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, 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, 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 noise 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, 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 <NUM> studs / dm<NUM>.

In accordance with an embodiment, 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, 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, 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, the radius is about <NUM>.

In accordance with an embodiment, 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 the following, some examples are provided, wherein any of these properties or any combination of these properties may be implemented in a studded tyre <NUM> according to the invention.

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

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

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

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

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

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

In accordance with an embodiment, the tread <NUM> of the tyre <NUM> comprises a mixture of two or more layers.

In accordance with an embodiment, the properties of the tyre <NUM> are such that a result of a road wear as measured according to SFS7503:<NUM>:en is less than <NUM> for a tyre of the size <NUM>/60R16 having load capacity of <NUM> (<NUM>), speed class <NUM>/h (T) and extra load (XL).

In accordance with an embodiment, the properties of the tyre <NUM> are such that a result of a road wear test as measured according to SFS7503:<NUM>:en is less than <NUM> and the load index (LI) of the tyre (<NUM>) is <NUM> or more.

In accordance with an embodiment, the properties of the tyre <NUM> are such that a result of the road wear of the tyre <NUM> as measured according to the standard SFS7503:<NUM>:en is less than <NUM> and the load index (LI) of the tyre (<NUM>) is <NUM> or more.

Claim 1:
A tyre (<NUM>) comprising
- a tread (<NUM>) having tread blocks (<NUM>);
- a plurality of stud holes (<NUM>); and
- a plurality of studs (<NUM>) installed in at least some of the stud holes (<NUM>),
- an arrangement of the studs (<NUM>) is such that less than two studs (<NUM>) are in a line in an axial direction (SAX) perpendicular to a rolling direction (R) of the tyre (<NUM>),
- within an area of a footprint less than two studs (<NUM>) are in the same line parallel to the rolling direction (R), and
- a distance between two adjacent studs is more than <NUM>,
characterized in that the tyre comprises a lamella-free area around each stud (<NUM>) so that a radius of the lamella-free area is more than <NUM>, more than <NUM>, more than <NUM>, more than <NUM> or more than <NUM>.