BACKGROUND OF THE INVENTION The grip wax of a ski has been traditionally applied to the grip zone of the ski base directly from a tin a tube by smoothing it with a suitable means.

The handling of the wax is messy and the result often uneven.

To overcome these problems, there has been developed a grip wax film which is industrially ap- plied as a uniform layer to a suitable substrate, such as e. g. a silicone paper. Strips of suitable length and width can be made from the paper which with the wax side facing downwards are pressed to the ski base in the grip wax zone. Depending on the grip wax film to be used, it either sticks directly to the ski base in a sticker-like manner, or by heating the film through a paper, it melts and is released from the pa- per, sticking to the ski base.

The films must be relatively thick, 0.05- 0.5mm, in order to achieve in one go a sufficient film of grip wax which lasts even for a rather long ski tour without a need for maintenance. Now it has been, however, noticed that the front edge of the grip wax that is formed in the front edge of the grip zone is problematic from the standpoint of the correct func- tioning of the ski whether one uses a film or waxes the ski with a conventional grip wax. The front edge of the grip wax is subjected to a lot of pressure, which results in that the snow strongly melts, water is formed, and the freezing starts from this zone. In this manner, the grip wax zone must be carefully de- termined for each skier specifically according to the

skier's weight and the skis to be used so that the grip wax zone only touches the surface of the track during the kick and not the glide.

One possibility to overcome this problem or at least to alleviate it is to always smooth the front edge of the grip wax film or of the grip wax layer to be continuous and completely smooth. This is, however, laborious and exactly what one wishes to avoid using a grip wax film, i. e. the waxing of a ski must be made as simple as possible without melting, rubbing and smoothing the waxes.

OBJECTIVE OF THE INVENTION The objective of the present invention is to eliminate the drawbacks referred to above.

One specific objective of the invention is to disclose a novel bottom structure of a ski which en- ables use as simple as possible of conventional grip waxes, such as klisters and transferable films of grip wax while at the same time achieving optimal grip and glide properties.

SUMMARY OF THE INVENTION The bottom structure of a ski in accordance with the invention is characterised by what has been presented in claims 1 and 9.

The bottom structure of a ski in accordance with the invention is designated to be used in con- junction with a grip wax film to be applied to the ski base as a uniform grip wax layer. The bottom structure comprises a grip wax zone in the middle section of the ski in the longitudinal direction thereof. According to the invention, the bottom structure comprises a substantially transverse step disposed in the front edge of the grip wax zone, the step extending along a

substantial portion of the width of the ski. The step extends inwards from the bottom plane of the ski so that at least the very front part of the grip wax zone is disposed deeper in the ski than the rear edge of the glide part that is disposed in front of the grip wax zone. Furthermore according to the invention, the height of the step is bigger or the same as the thick- ness of the grip wax film. In this manner, the top surface of the front edge of the grip wax film can be placed no further than so as to be in level with the bottom plane of the ski which is disposed in front of the grip wax zone, i. e. the grip wax zone begins con- tinuously or with a negative step so that the forma- tion of ice is prevented in the beginning of the grip wax zone.

In a preferred embodiment of the invention, the step extends along the entire width of the ski base from its one edge to the other. It is, however, possible that the step only extends along a portion of the ski's width, i. e. so that in the very fringes of the ski base there is a uniform and straight ski base but in the middle there is a step in accordance with the invention.

Preferably, the step forms a straight line from the ski's one end to the other. Similarly pref- erably, the step is perpendicular to the longitudinal direction of the ski. However, it is possible that the step is angular, curved-shaped or at an oblique angle with respect to the longitudinal direction of the ski.

More important is that the shape of the groove corre- sponds to the shape of the front edge of the grip wax film to be used so that no non-desired roughness in respect of glide and grip is formed in the section of the front edge of the grip wax zone.

In one embodiment of the invention, the step is substantially perpendicular with respect to the plane of the ski base, i. e. the notch formed by the

step is perpendicular. However, more substantial than the shape of the step is the height of the step so that the grip wax film that has been attached to the ski base behind the step is covered by the step, i. e. the height of the step is bigger or at least as big as the thickness of the film of grip wax.

Preferably, in the grip wax zone, the recess formed by the step gets back to the normal level of the bottom plane of the ski. This change back to the normal level must be continuous and uniform, prefera- bly curved-shaped so that the grip wax film does not form angles or sharp edges in any place which would easily lead to ice forming in the ski base. It is also possible that the steppedness caused by the step in the ski base is permanent, i. e. the grip wax zone in the ski base, as well as the glide surface of the ski base after the grip wax zone up to the ski tail are, to the tune of the height of the step, on a different plane than the front part of the ski before the grip wax zone.

Within the scope of the same inventive idea possible is also a bottom structure of a ski which is designated to be used in conjunction with a grip wax to be applied as a substantially uniform layer to the grip wax zone of the ski in the ski base. According to the invention, the bottom structure comprises, in the front edge of the grip wax zone, a substantially transverse step which extends along a substantial por- tion of the ski's width and extends inwards from the bottom plane of the ski. Furthermore, the height of the step is bigger or as big as the thickness of the grip wax layer to be applied to the grip wax zone be- hind the step. In this manner, the front edge of the grip wax need not be made thinner and ironed so as to have no steps; instead it is enough just to smooth the wax to the grip wax zone to form a suitable layer.

It is obvious that in this second embodiment of the invention it is possible to use also all the structures and shapes of the inventive step which have been described in more detail in conjunction with the embodiment that uses the grip wax film.

Although the invention is specifically char- acterised by the shape and structure of the front edge of the grip wax zone, it is also important that as the grip wax zone ends, no steps or other shapes are needed in the zone of the rear edge of the grip wax film or grip wax layer. In this zone, the ski base is even and has no steps in the longitudinal direction of the ski, and the wax film or wax layer just ends and the grip surface changes into the glide surface of the ski.

The bottom structure of a ski in accordance with the invention has considerable advantages com- pared to prior art. Thanks to the invention, the grip wax zone of a ski can be extended forward without the glide suffering. The grip wax zone is not as user and ski specific as conventionally, making it easier to determine the grip wax zone, and it can be clearly seen as extending backwards from the step when apply- ing the grip wax film or grip wax. Thanks to the in- vention, a better grip and glide can be achieved for a ski. As the invention prevents the formation of a front edge of a grip wax film or grip wax that makes the glide worse, the invention prevents the wearing off of the grip wax and eliminates the harmful phe- nomenon of freezing by reducing the pressure in the beginning of the grip wax zone.

LIST OF FIGURES In the following section, the invention will be described in more detail with reference to the ac- companying drawing, in which

Fig. 1 schematically represents a bottom structure in accordance with the invention as seen from the side and below; Fig. 2 represents a second embodiment of the invention as seen from the side; Fig. 3 represents a third embodiment of the invention as seen from the side; Fig. 4 represents a fourth embodiment of the invention as seen from the side; Fig. 5 represents a fifth embodiment of the invention as seen from below; Fig. 6 represents a sixth embodiment of the invention as seen from the side; Fig. 7 represents a seventh embodiment of the invention as seen from the side; Fig. 8 represents a straight front edge of a step as seen from below; Fig. 9 represents an oblique front edge of a step as seen from below; Fig. 10 represents a curved-shaped front edge of a step as seen from below; and Fig. 11 represents a two-piece front edge of a step as seen from below.

DETAILED DESCRIPTION OF THE INVENTION Fig. 1 shows one embodiment of the invention in which the base 2 of a ski 1 has a grip wax film 3 applied to the grip wax zone. In the front edge of the grip wax zone in the ski base there is an inward ex- tending step 4. The step is transverse and perpendicu- lar with respect to the longitudinal direction of the ski. Furthermore, the step extends along the entire width of the ski, i. e. from its one edge to the other.

The. height of the step is e. g. about 0.3mm and corre- sponds to the thickness of the grip wax film being used so that the height always is bigger or as big as

the thickness of the grip wax film. When placing the front edge of the grip wax film in this manner to the base of the step and the grip wax film backwards from this point to cover the entire grip wax zone, no shapes that would weaken the glide and contribute to the formation of ice are formed in the ski base.

In the embodiment of Fig. 2, the step 4, into which the front edge of the grip wax film 3 is placed, is relatively short in the longitudinal direction of the ski. In other words, the step itself is an edge which extends perpendicularly inwards of the ski; but backwards from the step, the ski base is relatively steeply sloping upwards, e. g. along a stretch of 10 meters, in a round-shaped and continuous manner to reach the level of the bottom plane of the ski, i. e. the level of the ski base before the step.

In the embodiment of Fig. 3, the step 4 gets back to the normal level of the bottom plane of the ski even in a more even and gentle manner. Also in this case, the change back to the normal level takes place in the grip wax zone, i. e. underneath the grip wax film 3, but possibly along a stretch of 100 to 150 mm.

In the embodiment of Fig. 4, after the step 4, the ski base will not be in level with the bottom plane of the ski which is disposed in front of the step; instead the surface of the grip wax film is dis- posed substantially in level with this plane along the entire length of the film, and the ski base remains on the lower level defined by the step up to the ski tail.

In the embodiments shown in Figs. 1-4, the step extends along the entire length of the ski, but it is not necessary. As can been seen from Fig. 5, the step 5 can extend along the entire width of the ski 1, i. e. narrow necks 6 are formed in the edges of the ski, in which necks the ski base extends uniformly

from the front of the grip wax zone, on both edges thereof, up to the rear of the grip wax zone. In that case, the grip wax film corresponds to the width of the step 5 in respect of its width so that it fits in the recess formed by the step and extends from it backwards in the ski base with the same width.

In Figs. 1 to 5, the step is upright and per- pendicular to the bottom plane of the ski. In the em- bodiment of Fig. 6, the step 7 is an oblique surface disposed a little backwards. In Fig. 7, in turn, the step 8 is formed by a ski's inwards curving, round- shaped surface. The embodiments shown in Figs. 6 and 7 are also possible, and they can be preferred embodi- ments in view of the manufacturing technique, the du- rability of the groove or the appearance. Substantial is that the heights of the steps to be used are suffi- cient in relation to the thickness of the grip wax film being used.

For the sake of clarity, Fig. 8 shows the straight step 4 in accordance with the invention as seen from below, the step extending in the base 2 of the ski perpendicularly with respect to the longitudi- nal direction of the ski from one end of the ski to the other.

Fig. 9 shows a second embodiment in which the step 9 extends also in a straight form in the base 2 of the ski from one end thereof to the other, but this straight line is at an oblique angle with respect to the longitudinal direction of the ski.

Fig. 10 shows a third embodiment in which the step 10 is curved-shaped and curves uniformly in the base of the ski from one end thereof to the other. The curved shape of the step can be curving in one direc- tion, as shown in the figure, i. e. e. g. a part of a curve of a sphere or of an ellipse, or it can be a step structure which curves into two directions.

Fig. 11 shows a fourth embodiment in which the step 11 is formed by two straight parts which are perpendicular with respect to the longitudinal direc- tion of the ski. These parts form a step in the longi- tudinal direction of the ski, i. e. they are disposed on different sides of the shoulder in the longitudinal direction of the ski.

The invention is not limited merely to the examples referred to above; instead many variations are possible within the scope of the inventive idea defined by the claims.