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. There is a constant need for improving grip and handling of tyres.

Grip is affected also by the ground on which the tyre is commonly used. Winter tyres, which are intended for icy roads, are commonly equipped with studs to improve grip on ice. However, the weather may change so that winter tyres need to be usable also on roads, on which there is water, slush, and/or snow. Naturally, also winter tyres need to be usable on dry road.

Grip on roads having water and/or slush are improved, when the water and/or slush is adequately driven away from a contact area between the road and the tyre tread. Thus, in principle, by using large grooves, water is well driven away. However, too many grooves and/or too large groove may worsen handling on bare roads and/or reduce grip, because stability of the tread blocks are reduced and tread blocks are more subject to deformation. Grip on snow, as well as on ice, may be improved by using softer material, provided by the softness of the rubber material as such and/or by sipes provided on the tread. However, too soft material and/or too many sipes may worsen handling.

In this field, the document <CIT> disclose a spike-embedded snow tire which comprises a tire tread, and a central pattern block, a crown pattern block and a shoulder pattern block which are integrated in the circumferential direction are arranged on the tire tread and jointly form a V-shaped pattern. The tire has excellent ice and snow performance.

In this field, the document <CIT> discloses a pneumatic tire provided with sipes, at least some of which have an open top end to the surface of the tread block. A first sipe is shaped in such a way, that at all depths (d) within a range from the open top of the first sipe to a first transition depth, the curved line includes at least one deflection point having an inner corner that has a radius of curvature under <NUM>.

In this field, the document <CIT> discloses car tyre having a tread that extends in axial direction for a width the tread including a central portion arranged across an equatorial plane, and two lateral portions opposed with respect to the central portion. The invention relates to a car tyre, in particular, an "all season" tyre for medium displacement cars.

In this field, the document <CIT> relates to automotive industry, namely, to tread pattern of a tire. Proposed tire comprises multiple circular main grooves extending in tire circumference and multiple running surfaces separated and composed by said circular main grooves in tread zone.

In this field, the document <CIT> discloses a tire tread for a pneumatic tire. It has a center rib and a series of steeply slanted grooves in each side region of the tread, the circumferentially adjacent grooves form blocks extending through the tread side regions. The center rib has a serrated configuration along each lateral side and a supporting chamfer extending from each serration point.

In this field, the document <CIT> discloses a pneumatic tire that includes circumferential main grooves extending in a tire circumferential direction and land portions partitioned and formed by the circumferential main grooves. The land portion of a center region and the land portions of left and right shoulder regions each have a plurality of sipes.

In this field, the document <CIT> discloses a winter tire providing an improved traction performance on the snow. A surface layer is so formed as to be thicker in a tread center region than in a tread shoulder region. Thus it is made easier for sipes to open in the tread center region, and the rigidity in the tread shoulder region is ensured.

In this field, the document <CIT> relates to modified polymer compositions including alpha-modified/omega-modified polymers and alpha-modified/branched modified polymers. The document also relates to the use of these compositions in the preparation of vulcanization compositions and articles prepared from these compositions. The modified compositions are used to prepare vulcanized and thereby crosslinked elastomeric compositions which have relatively low hysteresis losses. Such compositions are useful in many articles, including products with a good balance of low rolling resistance, good wet and ice grip combined with other desirable physical and chemical properties such as abrasion resistance, tensile strength and processing properties. tire tread.

In this field, the document <CIT> discloses a tire which can improve operational stability on a snow road surface and a dry road surface. Such a tire comprises a tread part provided with a plurality of first inclined grooves which extend from a first tread end toward a second tread end side with first inclination, and a first sub-groove which extends from each first inclined groove. The first sub-groove communicates with the first inclined groove, and extends to the first tread end side with second inclination.

In this field, the document <CIT> A discloses a studded tyre comprising a plurality of studs in which a pin is defined and has a configuration in plan view which is not symmetrical at least with respect to an axis, comprising a first side having a profile on which at least one tip is defined, and a second side having a substantially planar profile, said second side being opposite said first side. In order to improve the performance of a studded tyre, the studs are at least partly positioned in the tyre tread such that in a first plurality of studs, the pins have tips facing in a direction opposite to the advancing direction of the tyre.

In this field, the document <CIT> discloses a studded tire whose tread comprises a first part in contact with the ground and a second part arranged radially inside the first part, and at least one nail projecting from the tread and whose head is entirely anchored in the second part of the tread, in which the complex module G*( <NUM>) of the rubber composition forming the first part of the tread is less than <NUM> MPa and in which the complex modulus G* of the rubber composition forming the second part of the tread bearing changes as a function of the temperature such that G*(<NUM>) is greater than or equal to <NUM> MPa and G*(<NUM>) is less than or equal to <NUM>*(<NUM>).

It has been found how good handling and grip properties of a studded tyre can be simultaneously achieved. According to a first aspect of the invention, an average land ratio of the studded tyre is within a certain limit as detailed in the claims and in the description. According to a second aspect of the invention, a land ratio of a central area of a tread of the studded tyre is greater than either or both land ratios of the shoulder areas of the tread of the studded tyre. According to a third aspect of the invention, a density of sipes on a central area of a tread of the studded tyre is greater than a density/the densities of sipes on one or both of the shoulder areas of the tread of the studded tyre. These aspects are reflected in the independent claim as well as in the dependent claims.

<FIG> show different views of a stud. The different views/details have been indicated close to the number of the figure. Thus, e.g. <FIG> shows the view/detail Ib of <FIG>. This is indicated by the reference "(Ib)" near the figure number "<FIG>". In line with this, one can see the text "<FIG>" on the figure page <NUM>/<NUM>. Similar notation is used in other figures, too, as detailed below.

<FIG> shows a studded tyre <NUM>. A studded tyre <NUM> comprises a tread <NUM> and studs <NUM> provided in the tread <NUM>. Referring to <FIG>, the studs <NUM> have been installed into stud holes <NUM>. The stud holes may be made to the tread <NUM> during vulcanization of the tread material. The studded tyre <NUM> is a tubeless tyre, i.e. functional on a rim and without an inner tyre. In particular, the tyre may be a tyre for a vehicle of class M1 or N1 as defined in the Consolidated Resolution on the Construction of Vehicles (R. <NUM>), document ECE/TRANS/WP. <NUM>/<NUM>/Rev. <NUM>, para. These classes are:.

Referring to <FIG> and <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 specification, a "rib" is considered as a large tread block <NUM>. For example, the tread of <FIG> and <FIG> include a tread block that extends over the entire circumference of the tread <NUM>, 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. Moreover, in the tyre <NUM>, at least the pins <NUM> of the studs <NUM> are exposed on the tread <NUM> (see e.g. <FIG>).

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>.

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 or ground on which the vehicle equipped with the tyre used) 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. In this description, the total land area A220 refers to the area of only the radially outward facing side of the land portion.

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>. In this description, the total envelope area A210 refers to the area of only the radially outward facing side of the envelope surface, even if the envelope surface has also an inner side.

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 curved also 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 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. groove openings) between adjacent blocks and the blocks themselves. In other words, by 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 (the non-contacting area only) of the tread. To avoid possible confusion, the term land area is used throughout this description and in the meaning defined above.

According to the first aspect of the invention the average land ratio of the tyre <NUM> is <NUM> % to <NUM> %. Preferably, the average land ratio of the tyre <NUM> is <NUM> % to <NUM> %, and more preferably <NUM> % to <NUM> %. The most preferable value is about <NUM> %. This improves drainage of water and/or slush from underneath the studded tyre, when used on wet surface.

In general, increasing the land ratio improves the grip on dry road (including ice), but at the same time decreases the grip on wet and snowy roads (having water and/or slush). The range disclosed above has been found to provide an optimal compromise in studded tyres, which are used during winter.

As shown in Table <NUM> below, when the average land ratio increases, the grip on ice also improves.

For the data shown in Table <NUM>, three tyres (A, B, and C) were tested. The tyres A and C are identical except that A has been provided with studs, while the tyre C lacks studs. As expected, the tyre A performs much better on ice than the tyre C. For the tyre B, the average land ratio was increased, compared to the tyre A. In addition, the land ratio was optimized so that in the tyre B (unlike in the tyre A), the central land ratio was greater than the shoulder land ratio. In the Table <NUM> the acceleration, braking, circle handling, and ice handling results are given in relative terms. A higher number indicates better performance. As shown by the results, the grip and handling on ice improves when the average land ratio is increased. As indicated therein, the tyre B is superior compared to the tyre A.

According to the second aspect of the invention, a 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 (SR1 and CR; and CR and SR2) are shown by dash lines without a reference in <FIG>. The circumferential central line CL is also shown by a dash line. 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 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. 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.

The tread blocks <NUM> define the land portion LP of the tread and the envelope surface as detailed above.

The land portion LP of the tread has a central land area. The central land area is the area of the part of the land portion LP of the tread <NUM> that belongs to the central region CR. The land portion LP of the tread has a first shoulder land area. The first shoulder land area is the area of the part of the land portion LP of the tread <NUM> that belongs to the first shoulder region SR1. The land portion LP of the tread has a second shoulder land area. The second shoulder land area is the area of the part of the land portion LP of the tread <NUM> that belongs to the second shoulder region SR2. Reference is made to <FIG>.

The envelope surface (i.e. the combination of the land portion LP and the sea portion SP) has a central envelope area. The central envelope area is the area of the part of the envelope surface that belongs to the central region CR. The envelope surface has a first shoulder envelope area. The a first shoulder envelope area is the area of the part of the envelope surface that belongs to the first shoulder region SR1. The envelope surface has a second shoulder envelope area. The second shoulder envelope area is the area of the part of the envelope surface that belongs to the second shoulder region SR2. Reference is made to <FIG>; with the note that the envelope surface is the combination of the land portion (shown in <FIG>) and the sea portion (shown in <FIG>).

The tyre has a central land ratio of the tyre <NUM>. The central land ratio is defined as a ratio of the central land area to the central envelope area. According to the second aspect of the invention the central land ratio is <NUM> to <NUM> percentage points greater than either or both of a first shoulder land ratio and a second shoulder land ratio. Preferably, the central land ratio is <NUM> to <NUM> percentage points greater than either or both of a first shoulder land ratio and a second shoulder land ratio. More preferably, the first shoulder land ratio and the second shoulder land ratio are equal.

Herein the first shoulder land ratio is the ratio of the first shoulder land area to the first shoulder envelope area and the second shoulder land ratio is the ratio of the second shoulder land area to the second shoulder envelope area.

Thus, according to the second aspect of the invention proportionally more grooves are arranged in the shoulder region(s) SR1, SR2 than in the central region CR. This improves drainage of water and/or slush from underneath the tyre, when used on wet and/or snowy surface. This shows e.g. as widening of the grooves towards the sides of the tread, as clearly seen from <FIG>. It is noted that <FIG> shows, as an example, a tread <NUM> having such land ratios (and, optionally, an average land ratio, too) provided with studs 100a, 100b.

Naturally, the second aspect of the invention works particularly well when also the average land ratio is within the limits defined by the first aspect of the invention.

Preferably both the shoulder regions SR1, SR2 have substantially equal land ratios. Thus, preferably, a ratio of the first shoulder land ratio to the second shoulder land ratio is <NUM> to <NUM> such as <NUM> to <NUM>.

What has been said above concerning the land ratios of the tyre have been found to function well at least in tyre of the classes M1 or N1 (see above). This is also related to a width of the tread <NUM> of the tyre, since the water/slush is intended to be drained away from the contact area of the tread. Thus, preferably, the tyre <NUM> has a width W200 that is <NUM> to <NUM>. The width W200 of the tyre <NUM> is shown in <FIG>. Preferably also a first width W210 of the tread <NUM> is <NUM> to <NUM>. The first width W210 is shown in <FIG> and <FIG>.

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.

Such a tyre is preferably manufactured by vulcanizing a green tyre to form the tyre <NUM> and forming stud holes <NUM> to the tread <NUM> of the tyre <NUM> during the vulcanizing the green tyre.

To improve the grip, the tread <NUM> is sufficiently soft. The softness can be affected by tread material as such and by using sipes. 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>. In an embodiment, at least some of the tread blocks <NUM> are provided with sipes <NUM>. Preferably all the tread blocks <NUM> have been provided by at least one sipe <NUM>. Sipes <NUM> are shown in <FIG>, <FIG>.

A tyre having sipes is preferably manufactured by vulcanizing a green tyre to form the tyre <NUM> and forming the sipes <NUM> to the tread <NUM> of the tyre <NUM> during the vulcanizing the green tyre by using lamella blades.

In accordance with the third aspect of the invention, a density of sipes on a central region of a tread of the studded tyre is greater than a density of sipes on one or both of the shoulder regions of the tread of the studded tyre. Herein the term density of sipes refers to the total length of the sipes <NUM>, which open to the land portion LP of the tread, as divided by the area of the envelope surface. Thus, a unit of the density of sipes is a unit of a length divided by a unit of an area, e.g. cm/dm<NUM> or dm/dm<NUM>. Moreover, the length of the sipe <NUM> is defined at the level of the opening of the sipe <NUM>. Thus, the length of the sipes <NUM> measured on the tread surface.

More specifically, according to the third aspect of the invention, at least some of the tread blocks <NUM> of the central region CR of the tread <NUM> are provided with sipes <NUM> such that the tyre <NUM> has a first density of sipes <NUM>. Herein the first density of sipes refers to the density of the sipes in the central region CR. Thus, the first density of sipes <NUM> is defined as a total length of the sipes <NUM> arranged in the central region CR, the length measured on the tread surface, divided by the area of the central region CR. The area of the central region refers to the area of the part of the envelope surface that belongs to the central region, i.e. including the sea portion of the tread that belongs to the central region. More precisely, the total length of the sipes <NUM> arranged in the central region CR refers to the sum of the lengths of the sipes <NUM> (or parts thereof) that are arranged in the central region CR, the length of each sipe being measured on tread surface of the tyre. The tyre is preferably an unworn tyre.

At least some of the tread blocks <NUM> of the first shoulder region SR1 are provided with sipes <NUM> such that the tyre <NUM> has a second density of sipes <NUM>. Herein the second density of sipes refers to the density of the sipes in the first shoulder region SR1. Thus, the second density of sipes <NUM> is defined as a total length of the sipes <NUM> arranged in the first shoulder region SR1, the length measured on the tread surface, divided by the area of the first shoulder region SR1. The area of the first shoulder region SR1 is the area of the part of the envelope surface that belongs to the first shoulder region. More precisely, the total length of the sipes <NUM> arranged in the first shoulder region SR1 refers to the sum of the lengths of the sipes <NUM> (or parts thereof) that are arranged in the first shoulder region SR1, the length of each sipe being measured on tread surface of the tyre. The tyre is preferably an unworn tyre.

At least some of the tread blocks <NUM> of the second shoulder region SR2 are provided with sipes <NUM> such that the tyre <NUM> has a third density of sipes <NUM>. Herein the third density of sipes refers to the density of the sipes in the second shoulder region SR2. Thus, the third density of sipes <NUM> is defined as a total length of the sipes <NUM> arranged in the second shoulder region SR2, the length measured on the tread surface, divided by the area of the second shoulder region SR2. The area of the second shoulder region SR2 is the area of the part of the envelope surface that belongs to the second shoulder region. More precisely, the total length of the sipes <NUM> arranged in the second shoulder region SR2 refers to the sum of the lengths of the sipes <NUM> (or parts thereof) that are arranged in the second shoulder region SR2, the length of each sipe being measured on tread surface of the tyre. The tyre is preferably an unworn tyre.

In accordance with the third aspect of the invention the first density of sipes <NUM> is at least <NUM> % greater than either or both of the second density of sipes <NUM> and the third density of sipes <NUM>. Preferably, the first density of sipes <NUM> is at least <NUM> % greater than either or both of the second density of sipes <NUM> and the third density of sipes <NUM>. Preferably, the first density of sipes <NUM> is at least <NUM> % or at least <NUM> % greater than both of the second density of sipes <NUM> and the third density of sipes <NUM>. More preferably, the first density of sipes <NUM> is at least <NUM> % greater or at least <NUM> % than either or both of the second density of sipes <NUM> and the third density of sipes <NUM>. In a preferable embodiment, the second density of sipes is equal to the third density of sipes. In a preferable embodiment, the tyre is not antisymmetric.

The difference in the densities of sipes has the effect that the tread in the central region is less rigid than at the shoulder region(s) SR1, SR2. This improves grip on snowy surfaces.

Also preferably, the second and third densities of sipes are substantially equal. More specifically, preferably a ratio of the second density of sipes to the third density of sipes is <NUM> to <NUM>, more preferably <NUM> to <NUM>.

As an example, a tyre comprises, in the central region CR sipes <NUM> so that first density of sipes, i.e. the ratio of a total length of the sipes in the central region CR to an area of such a part of the envelope surface that belongs to the central region CR, is <NUM>/dm<NUM>. As conventional, dm<NUM> refers to square decimetre, i.e. (dm)<NUM>. The total length of the sipes in the central region CR is measured as defined above. Moreover, the tyre comprises such first and second shoulder regions SR1 and SR2 that are equally wide. The tyre comprises in the first shoulder region SR1 sipes so that the second density of sipes, i.e. a ratio of the total length of the sipes in the first shoulder region SR1 to an area of such a part of the envelope surface that belongs to the first shoulder region SR1, is <NUM>/dm<NUM>. The tyre is not antisymmetric, whereby the tyre comprises in the second shoulder region SR2 sipes so that the third density of sipes, i.e. a ratio of the total length of the sipes in the second shoulder region SR2 to an area of such a part of the envelope surface that belongs to the second shoulder region SR2, is also <NUM>/dm<NUM>. In this example, the tread consists of the central region CR, the first shoulder region SR1 and the second shoulder region SR2. Moreover, a width WCR of the central region CR was <NUM> % of the width W200 of the tyre <NUM>.

As calculatable from the values given above, in this specific example, the first density of sipes is <NUM> % greater than the second density of sipes. Since the second density of sipes equals the third density of sipes, the first density of sipes is <NUM> % greater than the third density of sipes.

An area of the envelope surface depends on the size of the tyre. However, the area may be e.g. of the order of <NUM> dm<NUM> to <NUM> dm<NUM> giving and idea of the total length of the sipes in the whole tread.

In addition, preferably, no sipe <NUM> is provided close to a stud hole <NUM>, in which a stud has been installed. Referring to <FIG>, a stud 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> 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>, or <NUM> to a centre of any one of the stud holes <NUM>. <FIG>and <FIG> show the distance DSS such that 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 e.g. <NUM>, or <NUM>. This has the effect that stud <NUM> is reliably fixed to its stud hole. 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>; as the studs improve grip only when present.

However, because the sipes <NUM> provide for additional grip through effective softening the tread and providing further edges of tread material, preferably at least one or some of the sipes are arranged reasonably close to the stud. Thus, in a preferable embodiment, a stud has been installed in a stud hole <NUM> such that a part of a sipe <NUM> is arranged closer than <NUM> to a centre of the stud hole <NUM>. More preferably, a stud has been installed in a stud hole <NUM> such that a part of a sipe <NUM> is arranged closer than <NUM> (or closer than <NUM>) Thus, in an embodiment, the tyre comprises such a stud and such a sipe that a distance from a part of the sipe to a centre of the stud hole <NUM> is, e.g., <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, <NUM> to <NUM>, or <NUM> to <NUM> (one significant digit, and in line with the text above, excluding the upper end-points of these ranges but including the lower end-points of these ranges). It is noted that the reference DSS only stands for such a measure that no part of any of the sipes <NUM> is arranged closer than the distance DSS to a centre of the stud hole <NUM>. to a centre of the stud hole <NUM>.

Most preferably, a stud 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> and a part of at least one of the sipes is arranged closer than <NUM> to a centre of the stud hole <NUM>. Preferably this applies to multiple studs so that parts of different sipes may be close to different stud holes. Thus, preferably, at least parts of multiple studs (<NUM>, 100a, 100b) are arranged in multiple stud holes <NUM> provided in multiple tread blocks <NUM>, and no part of any of the sipes <NUM> is arranged closer than <NUM> to a centre of any one of the stud holes <NUM>; and the tyre comprises multiple such sipes that a part of each one of the multiple sipes <NUM> is arranged closer than <NUM> (preferably closer than <NUM>) to a centre a stud hole <NUM> to which a stud has been arranged.

The third aspect of the invention may be used in combination with the first aspect of the invention (only). The third aspect of the invention may be used in combination with the second aspect of the invention (only). The third aspect of the invention may be used in combination with both the first and the second aspects of the invention. The first aspect of the invention may be used in combination with the second aspect of the invention, optionally without the third aspect of the invention.

In an embodiment, a width WSR1 of the first shoulder region equals a width WSR2 of the second shoulder region. The widths are shown in <FIG>. In an embodiment, a width WCR of the central region CR is <NUM> % to <NUM> % of the width W200 of the tyre <NUM>. In an embodiment, a width WCR of the central region CR is <NUM> % of the width W200 of the tyre <NUM>. The specific width WCR in connection with the different sipe densities and/or land ratios of central area and shoulder area(s) have been found particularly beneficial for the properties of the tyre.

In general a sipe <NUM> is a much narrower opening in the tread than a groove <NUM>. <FIG> show a width W240 of a sipe. In general, a width W240 of all the sipes <NUM> is less than <NUM>. Preferably, a width W240 of all the sipes <NUM> is less than <NUM>, most preferably, less than <NUM>.

In contrast, a groove <NUM> is wider. 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>. Notably, the widths W230 (and lengths) of the grooves <NUM> define the sea portion SP shown in <FIG>. In <FIG>, the groove <NUM> is arranged between a first tread block 220a and a second tread block 220b. The sipe <NUM> shown in these figure is arranged in the second tread block 220b. The stud <NUM> and the stud hole <NUM> in which the stud has been installed are arranged in the second tread block 220b.

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 at most equal to a depth D230 of one of the grooves <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. In an embodiment, a depth of all the sipes <NUM> is at least <NUM>.

In terms of depth, preferably an average of the depths D240 of the sipes <NUM> arranged in the first shoulder region SR1 of the tread <NUM> is not greater than an average of the depths D240 of the sipes <NUM> arranged in the central region CR. Likewise, preferably, an average of the depths D240 of the sipes <NUM> arranged in the second shoulder region SR2 of the tread <NUM> is not greater than an average of the depths D240 of the sipes <NUM> arranged in the central region CR. This has the effect that the sipes <NUM> provided in the shoulder region(s) SR1, SR2 do not soften the tread material too much by being too deep. This is related to handling of the tyre in the same way as the different densities of sipes detailed in connection with the third aspect of the invention. In a preferable 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 forward, 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 and a direction of rotation R as shown. In contrast the grooves of <FIG> and <FIG> define a full V-shape and a direction of rotation R as shown. Such a tread is what is commonly known as "directional" i.e. the tyre is designed to be fitted to the vehicle wheel in one particular way. This, together with the aforementioned land ratios improves the drainage of water and slush in regular use of the tyre.

As detailed above, the tyre <NUM> comprises studs <NUM>. An example of a stud <NUM> is shown in <FIG>. The direction Sz of the figures 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 a stud <NUM> is to improve grip of a tyre <NUM> on icy surfaces. Thus at least the pins <NUM> of the studs <NUM> are exposed on the tread <NUM> (see e.g. <FIG> and <FIG>). A protrusion P100 of a stud <NUM> measured from the envelope surface of the tread <NUM> is, in an embodiment, between <NUM> and <NUM>, more preferably between <NUM> and <NUM>, and most preferably between <NUM> and <NUM> measured from an inflated tyre. The tyre is an unworn 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 the claimed invention an average of a protrusions P100 of studs <NUM> measured from the envelope surface of the tread <NUM> is between <NUM> and <NUM>.

Referring to <FIG>, in an embodiment, a stud <NUM> comprises a body <NUM> and a pin <NUM>. The body <NUM> comprises a base flange <NUM> and a second part <NUM>, the second part <NUM> being joined to the base flange <NUM> and extending in the longitudinal direction Sz of the stud <NUM> from the base 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>.

The base flange <NUM> has a first cross-section on a plane that has a normal in the longitudinal direction Sz of the stud, the first cross-section having a first area A140. Moreover, the base flange <NUM> has a profile shape extending at least a certain distance in the direction of the normal of the first cross-section. As shown in <FIG>, the base flange <NUM> has the first cross-section on the plane that has a normal in the longitudinal direction Sz of the stud. <FIG>shows the cross-section Ie of the base flange <NUM>, the cross-section Ie indicated in <FIG>.

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>, the cross-section Ib indicated in <FIG>. Moreover, the first area A140 is greater than the second area A110.

In the embodiment of <FIG>, the second part <NUM> comprises a second flange <NUM> and a waist <NUM>. The waist <NUM> connects the base flange <NUM> to the second flange <NUM>. The pin <NUM> protrudes from the second flange <NUM> in the longitudinal direction Sz of the stud <NUM>. The second flange <NUM> may be called an upper flange.

The waist <NUM> has a third cross-section on a plane that has a normal in the longitudinal direction Sz of the stud, the third cross-section having a third area A132. <FIG>shows the cross-section Id of the waist <NUM>, the cross-section Id indicated in <FIG>.

Moreover, the second flange <NUM> has a fourth cross-section on a plane that has a normal in the longitudinal direction of the stud, the fourth cross-section having a fourth area A134. <FIG> shows the cross-section Ic of the second flange <NUM>, the cross-section Ic indicated in <FIG>.

The fourth area (that of the cross-section of the second flange <NUM>) is greater than the third area A132 (that of the cross-section of the waist <NUM>). The fourth area (that of the cross-section of the second flange <NUM>) is greater than the second area A110 (that of the cross-section of the pin <NUM>).

The first area A140 (that of the cross-section of the base flange <NUM>) is greater than a cross-section of the second part A130. A stud may comprise a second part <NUM> that does not comprise a waist and a second flange. In such a case the first area A140 (that of the cross-section of the base flange) is greater than the sole cross-section of the second part A130. However, the first area A140 may be greater than both of the third area A132 of the cross-section of the waist <NUM> and the fourth area A134 of the cross-section of the second flange <NUM>.

To provide a good grip of the stud <NUM>, the base flange <NUM> should be sufficiently large so that the dynamic impact, which the stud imposes to the road upon contact, is sufficient. Moreover, the pin should be sufficiently small in order to intrude well to ice. For these reasons, preferably, a ratio A140/A110 of the first area A140 to the second area A110 is <NUM> to <NUM>. Preferably, the ratio A140/A110 of the first area A140 to the second area A110 is <NUM> to <NUM>, and more preferably <NUM> to <NUM>.

Also, to provide a good grip, the pin <NUM> should protrude from second part <NUM> (e.g. from the second flange <NUM>) sufficiently. A first height H110, which is the first height that the pin <NUM> protrudes from the second flange <NUM> (or in the more general case, from the second part <NUM>) is depicted in <FIG>. As shown in <FIG>, the second part <NUM> extends in the longitudinal direction Sz of the stud <NUM> from the base 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>, the waist <NUM> and the second 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.

It has been found that for good grip, the first height H110 should be selected such that a ratio A140/H110 of the first area A140 to the first height H110 is <NUM> to <NUM><NUM>/mm. Preferably, the ratio A140/H110 of the first area A140 to the first height H110 is preferably <NUM> to <NUM><NUM>/mm, and more preferably <NUM> to <NUM><NUM>/mm. For fixing the stud firmly to stud holes, in an embodiment, the first area A140 is <NUM><NUM> to <NUM><NUM>, preferably <NUM><NUM> to <NUM><NUM>.

In an embodiment a mass of the stud <NUM> is <NUM> to <NUM>, preferably <NUM> to <NUM>, most preferably <NUM> to <NUM>. In an embodiment a mass of the pin <NUM> is <NUM> to <NUM>, preferably <NUM> to <NUM>. A length L110 of the pin <NUM> may exceed the first height H110. These measures are shown in <FIG>. The pin <NUM> may be e.g. inserted to a cavity of the second part <NUM> of the stud <NUM>. A sufficient length L110 of the pin <NUM> ensures that the pin <NUM> stays fixed in its position within the second part <NUM>. In an embodiment, a part of the pin <NUM> penetrates into the second part <NUM> of the body <NUM> of the stud <NUM>, e.g. to the second flange <NUM> of the second part of the stud, such that the length L110 of the pin <NUM> is at least <NUM> % of the first height H110. Preferably, a ratio of the length L110 of the pin <NUM> to the first height H110 is at least <NUM>, more preferably at least <NUM>. <FIG> shows how a part of the pin <NUM> penetrates into the second flange <NUM>, which is an example of the second part <NUM> of the body <NUM> of the stud <NUM>.

To keep the stud <NUM> in the stud hole <NUM> firmly, the first cross-section of the base flange <NUM> should be sufficiently large. In addition or alternatively, the stud <NUM> should be sufficiently long. Thus, in an embodiment, a height H100 of the stud, as measured in the longitudinal direction Sz of the stud <NUM> is greater than <NUM>. The height H100 is preferably <NUM> to <NUM>. Reference is made to <FIG>. Moreover (or alternatively), in an embodiment, a greatest one-dimensional measure dx140 of the first cross-section is <NUM> to <NUM>, preferably <NUM> to <NUM> and most preferably <NUM> to <NUM>. The measure dx140 is shown in <FIG>. In case the first cross-section of the base flange <NUM> would be circular, the greatest one-dimensional measure dx140 would be the diameter. However, typically, the first cross-section of the base flange <NUM> is not circular.

Moreover, in an embodiment, a length dn140 of a shortest straight line that connects an edge of the first cross-section, an opposite other edge of the first cross-section, and a central point O of the first cross-section is <NUM> to <NUM>, preferably <NUM> to <NUM>, and most preferably <NUM> to <NUM>. A shortest line that connects an edge of the first cross-section, an opposite other edge of the first cross-section, and a central point O of the first cross-section and the length dn140 thereof is shown in <FIG>. The central point O may refer to one of the following:.

These measures each one separately and some or all in combination ensure that the stud <NUM> remains well in the stud hole <NUM> in use, and therefore ensure good grip of the tyre <NUM>.

The second cross-section of the pin <NUM> may have various shapes. An example of the second cross-section is shown in <FIG>. Different examples are shown in <FIG>. The second cross-section of the pin <NUM>, the second cross-section being on a plane having normal to the direction Sz of the length of the stud, may be symmetric about one or several axes (the axis of symmetry being part of the plane of the cross-section).

Starting with forms having multiple axes of symmetry, <FIG>shows a cross-section of the pin, the cross-section being circular. A circle is symmetric about all axes that correspond to a diameter of the circle. Thus, the cross-section of <FIG> has infinitely many axes of symmetry. <FIG>and <FIG>show cross-sections having six axes of symmetry. 5d(ii) shows a shape of a regular hexagon, and 5d(iii) shows a star shape with six aisles. <FIG>shows a square, which has four axes of symmetry. The number nS of axes of symmetry S is shown in these figures. In all <FIG> the axes of symmetry S are shown by dash lines. The reference "S" is shown in <FIG>only and indicates an axis of symmetry.

<FIG>(both i and ii) show second cross-sections of the tip <NUM>, the second cross-sections have three axes of symmetry S (nS=<NUM>). <FIG>shows a triangle and <FIG>shows a star shape with three aisles, each aisle provided with curved edges.

<FIG> show second cross-sections of the tip <NUM>, the second cross-sections having two axes of symmetry S (nS=<NUM>). A basic form for some of these cross-section is a polygon with an even number of corners, optionally including rounded edges, the shape being stretched in one direction.

<FIG> show second cross-sections of the tip <NUM>, the second cross-section having only one axis of symmetry S (nS=<NUM>). A basic form for some of these cross-section is a polygon with an odd number of corners, optionally including rounded edges, the shape being stretched in one direction.

Preferable shapes of the tip <NUM> include such shapes that the second cross-section has one, two, or three (but not more than three) axes of symmetry. Thus, in an embodiment, the second cross-section has at least one and at most three axes such axes of symmetry S that belong to the plane of the second cross-section. Having one, two or three axes S of symmetry improves the possibilities of optimizing the grip by orienting the stud (e.g. one of the axes of symmetry) relative to the direction of rotation R. Thus, this number of axes S of symmetry is beneficial in combination with the tyre being directional (see above for definition).

The tyre comprises multiple studs. Preferably, the tyre comprises multiple such studs that have been disclosed above.

<FIG> shows a part of a tread <NUM> of a studded tyre <NUM>. Some of the studs holes <NUM> are shown without the studs <NUM>. As shown, 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>. Only some of the stud holes <NUM> to which studs <NUM>, 100a, 100b have been installed are shown by reference numerals.

All the studs <NUM> of the tyre <NUM> may be identical. Thus, in an embodiment, the tyre <NUM> comprises studs <NUM> of only a first stud type.

However, the tyre <NUM> may comprises at least two different types of studs. As shown in <FIG>, an embodiment of a studded tyre <NUM> comprises multiple studs 100a of a first stud type and multiple studs 100b of a second stud type. In <FIG>, the central region CR of the tread comprises studs 100b of the second stud type, and both the first shoulder region SR1 and the 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 type.

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 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, the studs 100a of the first stud type comprise 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 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, as shown in <FIG>, has the cross-section shown in <FIG>, and the pin <NUM> of the stud 100b of the first type, as shown in <FIG>, has the cross-section shown in <FIG>.

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, 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>. In an embodiment, 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>.

Concerning the latter, in an embodiment, the circumferential central line CL of the tread <NUM> defines a first half of the tread <NUM> and a second half of the tread <NUM>. 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> %.

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" stand 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.

Preferably the tyre <NUM> is configured such that a road wear of the tyre is minimized. Road wear of a tyre is defined as the road wear in the test specified in the standard SFS7503:<NUM>:en. The standard SFS7503:<NUM>:en specifies the test procedure in detail. On the general level, a vehicle equipped with the tyres to be tested is driven over test specimens with specified speed to a specific number of times. The average wear of test specimens is expressed in units of mass (i.e. in grams). The less the tyres wear the road, the less is the result (grams) of the test. In an embodiment, the multiple studs <NUM>, 100b, 100a and of the tyre <NUM> and the tread <NUM> of the tyre are configured such that a road wear of the tyre <NUM> as measured according to the standard SFS7503:<NUM>:en is less than <NUM>, preferably less than <NUM>, and more preferably less than <NUM>.

The road wear is correlated with a dynamic impact of the studs <NUM>. The low value of road wear may be achieved e.g. by having a sufficiently low dynamic impact of the studs 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 base flange <NUM> have effect on how sturdy the stud is supported to the rubber material of the tyre.

In addition to the tread <NUM> of the tyre <NUM>, the structure of the tyre <NUM> provides for sufficient rigidness of the tyre <NUM> and thereby also affect the handling 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> 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. 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 tyre size, tyre speed class, tyre purpose (winter/summer), tyre manufacturer and/or tyre name. The bead area of a tyre has a cable. The function of the cable and the bead area is to fit the tyre <NUM> to the rim.

The tyre <NUM>, in particular the carcass thereof, comprises a first ply <NUM>. The ply <NUM> may comprise fibrous material, e.g. Kevlar, polyamide, carbon fibres, or glass fibres.

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 textile belt <NUM> 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 comprised by a cap layer <NUM> of the tyre <NUM>. The cap layer <NUM> may further comprise material connecting the tread blocks <NUM>. Thus, the cap layer <NUM> forms at least part of a running surface of the tyre. Thus, the cap layer <NUM> forms at least part of an outer surface of the tread. 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 support the studs <NUM> so that they properly contact the ground in use. Thus, in an embodiment, the studs <NUM> of the tyre <NUM> are arranged at least partly on the underlayer <NUM>. Thus, the underlayer <NUM> affects the dynamic impact the studs have on the road.

Referring to <FIG>, <FIG>, in an embodiment the tyre <NUM> comprises the underlayer <NUM>. The underlayer <NUM> is made of a first rubber compound. Thus, in an embodiment, the tyre <NUM> comprises at least one ply <NUM>, at least one metal belt <NUM>, <NUM>, the cap layer <NUM> forming at least part of a running surface of the tyre, and the underlayer <NUM> made of a first rubber compound.

The underlayer <NUM> can be a circumferential layer. The underlayer <NUM> can be disposed radially outside an outermost belt of the tyre, such as a textile belt <NUM> or a metal belt <NUM>, <NUM>. If the tyre comprises a textile belt <NUM>, the underlayer <NUM> can be disposed radially outside the textile belt <NUM>. Technical effect of the textile belt is to restrict expansion from centrifugal forces during driving at high speed as well as improve many properties of the tyre having the underlayer, including improved handling, grip and aquaplaning for the tyre comprising the underlayer. If the outermost belt of the tyre is a metal belt <NUM>, <NUM>, the underlayer <NUM> can be disposed radially outside the metal belt <NUM>, <NUM>. The underlayer <NUM> has an inner surface <NUM> and an outer surface. The outer surface of the underlayer faces the tread <NUM>. The inner surface <NUM> of the underlayer substantially faces the center of the tyre <NUM>.

By the combined effect of the underlayer <NUM>, the ply <NUM>, and the metal belt or belts (<NUM>, <NUM>), the dynamic impact of the studs can be particularly well controlled at different ambient temperatures.

The underlayer <NUM> is preferably arranged at least partly below the studs <NUM>. Thus, the studs <NUM> can be placed at least partly above the underlayer <NUM>. Preferably, the underlayer <NUM> is arranged to be under each of studs of the winter tyre so that the base flange of the stud can be pressed against and retract into the underlayer <NUM>.

The stud <NUM>, preferably the base flange <NUM> of the stud, can be in direct contact with the underlayer <NUM>. Thus, preferably, there is no other material layer between the stud and the underlayer.

Preferably, at least part of a base flange <NUM> of a stud is surrounded by the underlayer <NUM>, and at least part of the second flange <NUM> of the stud is surrounded by the cap layer <NUM>. Technical effect is to support the stud and decrease road wear.

More preferably, also an intermediate layer <NUM> is used, and at least part of a waist <NUM> of the stud <NUM> is surrounded by the intermediate layer <NUM>. Technical effect is to improve stud retention as well as support the stud. More details of the intermediate layer <NUM> will follow.

The underlayer has an average thickness 21t. The average thickness 21t of the underlayer can be at least <NUM>, such as between <NUM> and <NUM>, more preferably at least <NUM>, and most preferably at least <NUM>. Furthermore, the average thickness 21t of the underlayer can be equal to or less than <NUM>, more preferably equal to or less than <NUM>, and most preferably equal to or less than <NUM>. The average thickness can be, for example, between <NUM> and <NUM>. Technical effect is that the ice grip properties of the stud can be substantially improved at cold weather, and moreover, the road wear at warm weather can be substantially reduced. Moreover, the underlayer of the presented thickness can be compressible to reduce road wear, to reduce tyre noise, to improve the driving performance of the tyre as well as to keep the pin of the stud protruded from the tread to provide the tyre with good grip on an icy driving surface.

In an embodiment, the underlayer has a hardness (ShA) between <NUM> ShA and <NUM> ShA, determined at an ambient temperature of <NUM> according to standard ASTM D2240. Herein (in below) the unit ShA refers to the Shore A hardness, i.e. hardness as determined in the "A" scale of the standard. Technical effect is that the underlayer <NUM> is able to reduce road wear at <NUM>. Preferably, the underlayer has a hardness (ShA) between <NUM> ShA and <NUM> ShA, more preferably between <NUM> ShA and <NUM> ShA, determined at an ambient temperature of <NUM> according to standard ASTM D2240. These values may apply also at <NUM>.

Preferably, the tyre has such an underlayer <NUM> that a hardness of the underlayer varies with the temperature. Technical effect is to decrease the road wear of the studded tyre but still provide desired winter grip properties in spite of the reduced road wear. Hardening/softening of the material may occur at a temperature that can be chracterized by a measuring part of of a complex modulus of the material as discussed below. In particular, a position of a tan delta maximum of the material may characterize a temperature at which hardening/softening takes places.

In an embodiment, a position of a tan delta maximum of the underlayer <NUM> is configured to be between -<NUM> and +<NUM>, determined according to ISO <NUM>-<NUM> (<NUM>) in compression. Technical effect is that in warm conditions, the underlayer can substantially soften, whereby the underlayer can allow the stud body to retract into the tread of the tyre, whereby it can reduce the stud's dynamic impact and thereby reduce the wear of the road.

The position of the tan delta maximum refers to the temperature at which tan delta reaches its maximum value. As background, the values of tan delta, as function of temperature, is referred to as a tan delta curve. The values for tan delta curve of this specification are determined as follows: Dynamic Mechanical Thermal Analysis ("DMTA") tests provide information about the small-strain mechanical response of the samples as a function of temperature. Sample specimens can be tested using a commercially available DMTA equipment in compression mode according to the standard ISO <NUM>-<NUM> (<NUM>). The specimen is cooled to -<NUM>° C and then heated to <NUM>° C at a rate of <NUM>/min (i.e. <NUM>/min) while subjected to an oscillatory deformation and a static strain, the oscillatory deformation having a frequency. Examples of specific values are detailed below. The output of the DMTA test is the storage modulus (E') and the loss modulus (E"), both as function of temperature. The storage modulus indicates the elastic response or the ability of the material to store energy, and the loss modulus indicates the viscous response or the ability of the material to dissipate energy. The ratio of E"/E', called tan delta, gives a measure of the damping ability of the material. As discussed, tan delta depends on temperature. Peaks in tan delta are associated with relaxation modes for the material, such as glass transition. The term "position of tan delta maximum" refers to a temperature in which the maximum value of a tan delta curve is obtained. Thus, "position of tan delta maximum" can be determined, for example, as a position of maximum tan delta value of the tan δ curve.

The tan delta values can be determined from rubber compounds of a tyre as well as from rubber compounds to be used for a tyre, before forming the tyre. The sample has dimensions of diameter <NUM> × height <NUM>, when determined from a tyre. Further, the sample has dimensions of diameter <NUM> × height <NUM>, when determined from a rubber compound.

As for the values of oscillatory deformation and a static strain, for example, the following value can be used in the DMTA measurements:.

The position of a tan delta maximum of the underlayer is thus the temperature at which the tan delta of the underlayer reaches it maximum. Correspondingly, the position of a tan delta maximum of the intermediate layer is the temperature at which the tan delta of the intermediate layer reaches it maximum.

From the DMTA measurements, also the dynamic stiffness (E*) of the material (underlayer of intermediate layer, whichever is tested) can be detremined as detailed in the standard ISO <NUM>-<NUM> (<NUM>) in a compression test. The values can be determined from rubber compounds using the procedure disclosed above for tan delta.

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.

The dynamic stiffness (E*, MPa) of the underlayer 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 tyre 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 tyre at different temperatures can be more controllable, and the grip properties of the winter tyre 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.

These properties of the underlayer <NUM> can be achieved by a proper composition of the material of the underlayer <NUM>.

Preferably, the underlayer <NUM> contains.

A combined amount of carbon black and/or silica (examples of reinforcing fillers) is preferably from <NUM> to <NUM> phr, more preferably from <NUM> to <NUM> phr.

Technical effect of materials comprising the rubbers comprising at least <NUM> phr solution polymerized styrene-butadiene rubber together with the reinforcing filler(s) and the resin(s), and preferably also <NUM> to <NUM> phr NR, BR, and/or IR, is to provide the desired tan delta curve for the rubber compound.

The underlayer <NUM> can further contain additives, such as one or more of oils, antidegradants, ZnO, stearic acid, vulcanization chemicals and sulphur.

As discussed, the reinforcing fillers can comprise carbon black, and/or silica.

If the reinforcing fillers comprise silica, silane can be added for improving reinforcing efficiency of the silica. Preferably, a content of the silane is equal to or less than <NUM>% by weight, such as between <NUM> wt. % and <NUM> wt. %, determined from total weight of the silica in the underlayer. Technical effect it to provide improved dispersion. Furthermore, silane can form bonds between silica and rubber during the vulcanization.

As discussed, the underlayer <NUM> preferably contains styrene butadiene rubber which is solution-polymerized styrene butadiene rubber SSBR. The underlayer <NUM> can comprise at least <NUM> phr of SSBR. Thus, the content of SSBR in the underlayer <NUM> can be at least <NUM> phr, preferably at least <NUM> phr, more preferably at least <NUM> phr, and most preferably at least <NUM> phr. Further, the content of SSBR in the underlayer <NUM> can be equal to or less than <NUM> phr, preferably equal to or less than <NUM> phr, more preferably equal to or less than <NUM> phr, and still more preferably equal to or less than <NUM> phr. By using said contents of the solution-polymerized styrene butadiene rubber SSBR, the stiffness can be efficiently adjusted as desired.

Microstructure of SSBR has an effect on properties of the SSBR. When preparing the underlayer, the vinyl content of the solution-polymerized styrene butadiene rubber, is preferably between <NUM>% and <NUM>% by weight, more preferably between <NUM>% and <NUM>% by weight, wherein the vinyl contents are expressed in mol % relative to the butadiene. Furthermore, the styrene content of the styrene butadiene rubber is preferably between <NUM>% and <NUM>% by weight, most preferably between <NUM>% and <NUM>% by weight, wherein the styrene content is expressed in mass % relative to the whole polymer. The contents can be determined by <NUM>-NMR method in accordance with ISO <NUM>-<NUM>:<NUM>.

This embodiment can provide particularly suitable properties for the underlayer so that stiffening of the underlayer can take place in a controlled manner. Thus, stiffening can take place at a moment determined more precisely in advance.

Preferably, the underlayer contains either NR and SSBR, or BR and SSBR. In these combinations, the technical effect of NR and BR is to improve the elasticity of the underlayer even at cold temperatures. Further, the technical effect of SSBR is to improve stiffness of the mixture.

Thus, advantageously, the underlayer contains.

Technical effect of said combination of NR and SSBR is that the position of tan delta maximum can be efficiently adjusted as desired, and hardness of the underlayer can increase at a desired temperature, particularly when used together with the reinforcing fillers and resins according to this specification. Furthermore, thanks to this combination, elasticity of the underlayer can be maintained at cold temperatures, further improving properties of the underlayer.

It is to be noted that the natural rubber NR can be replaced with a synthetic isoprene rubber and still maintain the technical effects of the natural rubber. The synthetic isoprene rubber IR is very much like natural rubber but made synthetically. Thus, from <NUM> to <NUM> wt. % of the natural rubber NR can be replaced with the synthetic isoprene rubber IR.

In an embodiment, the underlayer advantageously contains.

Technical effect is that properties of the studded tyre having the underlayer can be particularly improved and position of the tan delta maximum of the underlayer can be easily adjusted by using said amounts of polybutadiene rubber and the solution polymerized styrene-butadiene rubber, particularly when used together with the reinforcing fillers and resins according to this specification.

The underlayer <NUM> can contain reinforcing fillers. A total amount of the reinforcing fillers is preferably more than <NUM> phr, more preferably at least <NUM> phr, still more preferably at least <NUM> phr, and most preferably at least <NUM> phr, determined from the underlayer <NUM>. Furthermore, the underlayer <NUM> can comprise equal to or less than <NUM> phr of reinforcing fillers, preferably equal to or less than <NUM> phr of reinforcing fillers, still more preferably equal to or less than <NUM> phr of reinforcing fillers, and most preferably equal to or less than <NUM> phr of reinforcing fillers. Technical effect of the reinforcing fillers is that the hardness of the underlayer is easier to optimize to a desired level.

The reinforcing fillers are preferably selected from silica and carbon black. The reinforcement may comprise both silica and carbon black. If the reinforcing fillers comprises silica, also silane is preferably added to the mixture. Technical effect of the reinforcing fillers is to improve the strength of the underlayer. Furthermore, the reinforcing fillers can be used to influence the ShA hardness of the underlayer so that the hardness of the underlayer can be more easily optimized to a desired level.

In a non-limiting embodiment, the carbon black is selected from N375 and N234. These carbon blacks are known by a person skilled in the art.

In an embodiment, silica can be selected from: anhydrous silica prepared by dry process and silica prepared by wet process. Among them, hydrous silica prepared by wet process is preferable because it contains a lot of silanol groups.

In a non-limiting embodiment, the silica is selected from high BET and low BET.

Silane coupling agent can be used for silica to be appropriately dispersed during kneading. Preferably, a content of the silane is between <NUM> wt. % and <NUM> wt. %, determined from total weight of the silica in the underlayer. Technical effect it to provide improved dispersion. Furthermore, silane can form bonds between silica and rubber during the vulcanization.

The silane coupling agents can be of any type known to those skilled in the art. For example, at least one of bifunctional organosilane and polyorganosiloxane can be used. "Bifunctional" means a compound having a first functional group capable of interacting with silica, e.g., alkoxy, cycloalkoxy or phenoxy group as a leaving group on the silicon atom, and a second functional group capable of interacting with the double bond of elastomer, e.g., -SCN, -SH, -NH2 or -Sx - where x = <NUM> to <NUM>. The organosilanes can be chosen from the group consisting of polysulphide organosilanes (symmetrical or asymmetrical) such as bis(<NUM>-triethoxysilylpropyl) tetrasulphide, abbreviated as TESPT or bis disulphide - (triethoxysilylpropyl), abbreviated as TESPD, polyorganosiloxanes, mercaptosilanes or blocked mercaptosilanes.

The underlayer <NUM> can contain oil(s). The amount of oils, if used, can be at least <NUM> phr, more preferably at least <NUM> phr, and most preferably at least <NUM> phr. Further, the amount of oils can be equal to or less than <NUM> phr, preferably equal to or less than <NUM> phr, and most preferably equal to or less than <NUM> phr. Technical effect is to increase processability and adjust hardness of the compound.

The oil(s) is/are preferably selected from the group of:.

Preferably, said oil contains or consists of at least primarily TDAE oil and/or SRAE oil. Technical effect of oils is to act as process aids and softeners in the manufacturing process.

As discussed, the underlayer <NUM> can contain one or more resins. A total content of resins is preferably at least <NUM> phr determined from the underlayer. Technical effect is that the resins can adjust dynamic behavior of the underlayer by shifting and/or broadening the tan delta peak of the rubber compound. Thus, thanks to the resins, position of the tan delta maximum can be adjusted in a cost-efficient and controlled manner to a predetermined temperature range.

A total amount of resins can be at least <NUM> phr, preferably at least <NUM> phr, more preferably at least <NUM> phr, and most preferably at least <NUM> phr, determined from the underlayer. Further, the total amount of resins can be equal to or less than <NUM> phr, preferably equal to or less than <NUM> phr, more preferably equal to or less than <NUM> phr and most preferably equal to or less than <NUM> phr, determined from the underlayer. Thus, the total amount of resins can be, for example, <NUM>-<NUM> phr, preferably <NUM>-<NUM> phr, and more preferably <NUM>-<NUM> phr, determined from the underlayer. By applying resin, position of tan delta maximum of the underlayer can be raised by a predetermined level so that the hardening of the underlayer can be implemented within a predetermined temperature range. Another technical effect is that by using the preferably ranges, resins affect the rubber compound by shifting and/or broadening the tan delta peak of the rubber compound as desired.

The resin(s) used for the underlayer can have a glass transition temperature higher than <NUM>, more preferably higher than <NUM>, and most preferably higher than <NUM>. Further, the resin(s) used for the underlayer can have a glass transition temperature of less than <NUM>, preferably less than <NUM>, most preferably less than <NUM>. For example, the resin(s) can have a glass transition temperature from <NUM> to <NUM>, preferably from <NUM> to <NUM>. As discussed, Tg for resins can be determined as a peak midpoint by a differential scanning calorimeter (DSC) at a temperature rate of increase of <NUM> per minute, according to ASTM D6604 or equivalent.

Preferably, the one or more resins of the underlayer are selected from the following group:.

Technical effect is to efficiently adjust the position of tan delta maximum to a desired temperature, i.e., to shift a position of tan delta maximum to a desirable range.

Most preferably, the one or more resins of the underlayer are selected from rosin-based resins, terpene-based resins, and pure monomer C9 resins (PMR), i.e., aromatic resins based on aromatic feedstocks that have been highly purified prior to polymerization, including copolymers of styrene and α-methylstyrene. Technical effect is to shift tan delta peak position to a desirable temperature range more efficiently.

The underlayer can comprise an aromatic resin. Thus, the resin(s) can contain aromatic groups. In an embodiment, the resins contain more than <NUM> % aromatic groups, more preferably more than <NUM> % aromatic groups. However, the aromatic content is preferably less than <NUM>%, more preferably equal to or less than <NUM>%.

Advantageously, for adjusting the position of the tan delta peak of the underlayer to a desired temperature range in a controlled and precise manner, the underlayer comprises:.

The contents of the materials are preferably in the range defined in this specification.

The underlayer <NUM> can comprise, primarily comprise, or consist of a material whose tan delta maximum is at a temperature of 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, tan delta maximum of said material can be at a temperature equal to or less 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. Technical effect of the preferable ranges is that the hardening of the underlayer can take, more accurately, place at a point optimal in view of road wear and winter grip hence, the stud's dynamic impact of the tyre can be controlled easier at different temperatures.

An unvulcanized material of the underlayer can be vulcanized so that sulphur is used as the vulcanizing agent.

As indicate above, the underlayer <NUM> may be reasonably soft at a high temperature. However, it has been found that a too soft underlayer <NUM> may not result in optimal handling properties of the tyre. The inventors have found that the handling properties can be, in such a case, improved by using an intermediate layer <NUM> providing for sufficient rigidness, even if the underlayer <NUM> is soft. This applies in particular, when the underlayer <NUM> is made of adaptive material, i.e. material that softens at high temperatures as discussed above. Thus, in an embodiment, the tyre <NUM> comprises comprises the intermediate layer <NUM>. Moreover, in such an embodiment, the underlayer <NUM> is arranged, at least partially, under the intermediate layer <NUM>. The intermediate layer <NUM> can be a circumferential layer.

<FIG> show embodiments comprising the intermediate layer <NUM>. The intermediate layer <NUM> can be arranged between the cap layer <NUM> and the underlayer <NUM>, at least on locations of the studs. Technical effect is that the intermediate layer improves the stability of the tyre and supports the studs <NUM> therein when the underlayer is softening. The intermediate layer <NUM> can support the studs and hence improve driving stability of the tyre on a dry road.

Even if not shown, a part of the intermediate layer <NUM> may form a part of the cap layer <NUM>. Thus, in an embodiment, the intermediate layer <NUM>, or at least part of the intermediate layer <NUM>, is be placed between the cap layer <NUM> and the underlayer <NUM>.

An average thickness 22t of the intermediate layer can be at least <NUM> preferably at least <NUM>. As for an upper limit, the thickness of the intermediate layer may be at most <NUM>. A preferable range for the thickness is at least <NUM> and less than <NUM>, more preferably at least <NUM> and equal to or less than <NUM>, and most preferably in a range between <NUM> and <NUM>. Technical effect is that the intermediate layer can, together with the underlayer, provide the stud with particularly suitable winter grip properties. Thus, the ice grip properties of the tyre can be substantially improved. In addition, properties of the vehicle tyre can be designed as desired more efficiently than in other solutions.

A thickness of the intermediate layer <NUM>, determined at a location wherein the intermediate layer is surrounding a stud, can be at least <NUM> and equal to or less than <NUM>, preferably at least <NUM>, more preferably at least <NUM> and less than <NUM>, still more preferably at least <NUM> and equal to or less than <NUM>, and most preferably in a range between <NUM> and <NUM>. Technical effect is that the intermediate layer can support the stud. Further technical effect is that the intermediate layer can provide particularly suitable handling properties.

The intermediate layer <NUM> is made of a second rubber compound. In an embodiment, the intermediate layer has a hardness (ShA) between <NUM> ShA and <NUM> ShA, determined at an ambient temperature of <NUM> according to standard ASTM D2240. Technical effect is that the intermediate layer is able to improve stability of tyres having the underlayer <NUM>. Preferably, intermediate layer has a hardness (ShA) between <NUM> ShA and <NUM> ShA, determined at an ambient temperature of <NUM> according to standard ASTM D2240. These values may apply also at the temperature <NUM>.

A position of tan delta maximum of the intermediate layer <NUM> is, in an embodiment, configured to be between -<NUM> and -<NUM> (more preferably between -<NUM> and -<NUM>), determined according to ISO <NUM>-<NUM> (<NUM>) in compression. Further, preferably, at the same time, a position of a tan delta maximum of the underlayer <NUM> can be configured to be between -<NUM> and +<NUM> (preferably between -<NUM> and +<NUM>), determined according to ISO <NUM>-<NUM> (<NUM>) in compression. Thus, when the underlayer substantially softens in warm conditions, the intermediate layer can substantially maintain its stiffness and therefore support the stud and the whole tyre.

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 tyre and the studs of the tyre at the warmer temperature. At the same time, 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.

The composition of the intermediate layer <NUM> affects these properties.

The intermediate layer can comprise or be made of materials selected from a group comprising or consisting of:.

In an embodiment, silica may be selected from: anhydrous silica prepared by dry process and silica prepared by wet process. Among them, hydrous silica prepared by wet process is preferable because it contains a lot of silanol groups. Silane coupling agent can be used for silica to be appropriately dispersed during kneading.

If the fillers comprise silica, silane can be added for improving reinforcing efficiency of the silica. Preferably, the content of the silane is equal or less than <NUM>% (such as from <NUM>% to <NUM>%) by weight relative to the amount of silica. Technical effect is to improve dispersion and during the vulcanization silane forms bond between silica and rubber.

Most preferably, the intermediate layer comprises.

As discussed, in an embodiment, the intermediate layer is made of an electrically conductive rubber material.

Preferably, the intermediate layer <NUM> comprises a rubber reinforcing carbon black. Technical effect is to increase stiffness of the intermediate layer while improving electrical conductivity through the tread. The intermediate layer can comprise a rubber reinforcing carbon black content of at least <NUM> phr, preferably at least <NUM> phr. Thus, the rubber composition(s) of the intermediate layer <NUM> can be relatively electrically conductive. Thus, the relatively electrically conductive rubber composition of the intermediate layer can e.g., form a part of the electrically conductive path. Thus, a very small electrical resistance can be obtained through the cap layer.

The intermediate layer <NUM> can comprise one or more oils. The oil(s) can comprise, for example,.

Preferably, the oil(s) are selected from TDAE and SRAE. The oils can act in the manufacturing process as process aids and softeners.

A total amount of the oils in the intermediate layer <NUM> can be from <NUM> to <NUM> phr.

The resin(s) of the intermediate layer can be selected from the following group:.

A total amount of the resins in the intermediate layer <NUM> can be from <NUM> phr to <NUM> phr, preferably <NUM> to <NUM> phr. Technical effect of resins is fine tuning stiffness properties of the intermediate layer.

Thanks to the underlayer and the intermediate layer, properties of the tyre 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. Further, by the combined technical effect of the intermediate layer and the underlayer, wear of the road surface under non-frozen conditions can be reduced while the underlayer together with the intermediate layer substantially improves winter grip of the tyre on an icy road.

As for the relation of the hardnesses of the underlayer <NUM> and the intermediate layer <NUM>, in an embodiment, hardness (ShA) of the intermediate layer is configured to be greater than hardness of the underlayer at <NUM>. Said difference between the underlayer and the intermediate layer is preferably at least <NUM>%, more preferably from <NUM>% to <NUM>%, and most preferably from <NUM>% to <NUM>% so that underlayer is at least <NUM>% softer than the intermediate layer, determined at <NUM>. Technical effect is that the underlayer yields to a suitable extent at said ambient temperature, which reduces wear of the road surface, while the harder intermediate layer supports the tyre.

In an embodiment, the first rubber compound has a first hardness (ShA) and the second rubber compound has a second hardness (ShA), and a hardness (ShA) difference between the first rubber compound and the second rubber compound is at least <NUM>% determined at -<NUM> so that the second rubber compound is at least <NUM>% softer than the first rubber compound, determined according to standard ASTM D2240 with an exception that the hardness is determined at a temperature of -<NUM> and the rubber compounds are tempered according to Table <NUM> of the specification. Technical effect is that the underlayer made of the first rubber compound substantially improves ice grip of the tyre on an icy road.

The hardness (ShA) difference between the underlayer and the intermediate layer at cold temeperatures is preferably at least <NUM>%, more preferably from <NUM>% to <NUM>%, still more preferably from <NUM>% to <NUM>%, and most preferably from <NUM>% to <NUM>% so that the underlayer is harder than the intermediate layer, determined at -<NUM>. Technical effect is that the underlayer and the intermediate layer substantially improves ice grip of the tyre on an icy road.

Accordingly, when measuring the Shore hardness at a temperature which is not dislcosed in the standard ASTM D2240; the Shore hardness is measured by first tempering the material to be measured at the reference temperature by keeping the material to be measured at the reference temperature for a time given in Table <NUM> before the measurements.

A softer underlayer material can substantially increase the retraction of the stud into the tyre at warmer temperatures and thereby reduce road wear and noise. The greater the difference in hardness of the material at different temperatures, the greater the effect of the underlayer on the grip of the tyre in cold weather and on road wear in warm weather. Thus, the effects of the underlayer can be particularly advantageous for both cold and warm conditions.

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 tyre can be substantially improved while the intermediate layer supports the whole tyre and the studs of the tyre 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 tyre 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 tyre. 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 tyre can be substantially improved, and, for example, the braking distance needed by the winter tyre under certain conditions can be substantially reduced.

It was noted during experimental tests that properties of tyres were particularly improved when the position of tan delta maximum of the underlayer was in a range between <NUM> and <NUM>, and the position of tan delta maximum of the intermediate layer was less than -<NUM>. Thus, preferably, the tan delta peak position of the underlayer is in a range between <NUM> and <NUM>, and the tan delta peak position of the intermediate layer is equal to or less than -<NUM>.

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

During the experimental tests, it was noted that properties of tyres were particularly improved when a cross point of stiffness curves of the underlayer and the intermediate layer (shown in Fig. 6b) was in a range between +<NUM> and <NUM>, and particularly when the cross point of stiffness curves was in a range between +<NUM> and <NUM>.

Thus, advantageously, a cross point of stiffness curves of the underlayer and the intermediate layer is in a range between +<NUM> and <NUM>, more preferably in a range between +<NUM> and <NUM>.

In an advantageous embodiment, the dynamic stiffness of the underlayer is higher than the dynamic stiffness of the intermediate layer at temperatures of less than <NUM>, but 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 substantially reduce road wear while improving handling properties of the tyre.

As for the materials of the underlayer <NUM> and the intermediate layer <NUM>, several studded tyres comprising the underlayer and the intermediate layer according to this specification were manufactured. The amounts of raw materials were as disclosed in the specification.

Table <NUM> discloses, as an example, raw materials of the underlayer and the intermediate layer for one of the manufactured tyres.

The rubber mixtures were obtained by means of a stepwise mixing process. A <NUM>-internal mixer (Krupp Elastomertechnik GK <NUM>,<NUM> laboratory mixer) was used to add the compounds.

In the first step, the polymers were added and mixed for <NUM> seconds. In the second step, part of the carbon black and chemicals were added and mixed for <NUM> seconds. In the third step, the rest of the carbon black and oil were added and mixed for <NUM> seconds or temperature in mixing chamber received <NUM> degrees.

The final step with curing chemicals was performed at <NUM> for <NUM> seconds.

DMTA samples were vulcanized at <NUM> by using a pressure of <NUM> bar. The optimum vulcanization time of t90 (at <NUM>) was determined with a moving die rheometer according to ISO <NUM> (<NUM>). A vulcanization time of t90 plus <NUM> was used for the samples.

Position of tan delta max, DMTA at <NUM> and at -<NUM>, and hardness (ShA) at <NUM> were determined from the obtained underlayer and intermediate compounds.

DMTA measurements results of Table <NUM> were done by using tension mode according to standard ISO <NUM> (<NUM>), by using a temperature range from - <NUM> to <NUM>, <NUM>, static strain <NUM>%, and dynamic strain ± <NUM>,<NUM> %.

Claim 1:
A tyre (<NUM>) comprising
- a tread (<NUM>) comprising tread blocks (<NUM>) such that grooves (<NUM>) are arranged between the tread blocks (<NUM>) and
- studs (<NUM>, 100a, 100b) installed into at least some of the tread blocks (<NUM>), wherein
- the tread blocks (<NUM>) define
∘ a land portion of the tread (<NUM>), the land portion consisting of the parts of the tread blocks (<NUM>) and the studs (<NUM>, 100a, 100b) arranged to contact a surface in use of the tyre (<NUM>), the land portion having a total land area (A220), and
∘ an envelope surface consisting of the land portion of the tread (<NUM>) and the regions defined by the openings of the grooves (<NUM>), the envelope surface having a total envelope area (A210),
- an average land ratio of the tyre (<NUM>), the average land ratio being defined as a ratio (A220/A210) of the total land area (A220) to total envelope area (A210), is <NUM> % to <NUM> %
- at least some of the tread blocks (<NUM>) are provided with sipes (<NUM>), and
- at least a part of one of the studs (<NUM>, 100a, 100b) is arranged in a stud hole (<NUM>) provided in one of the tread blocks (<NUM>)
characterized in that
- no part of any of the sipes (<NUM>) is arranged closer than <NUM> to a centre of the stud hole (<NUM>) and
- an average of a protrusions (P100) of studs (<NUM>) measured from the envelope surface of the tread (<NUM>) is between <NUM> and <NUM>.