the basic concept of the present invention is to make supplemental traction - promoting systems , namely special chains or a gravel spreader or other supplemental options , come into play automatically by linkage with an existing traction control ( asr ), so that the traction behavior and stability of a motor vehicle so equipped can be decisively improved . in the drawing , the asr system , which can also be called a drive slip limiting or traction control system , is not shown separately , nor is an anti - skid or abs system normally linked with such an asr system , because both systems are quite well known per se and need not be described here . it will also be understood that beyond the hardware components shown in fig1 a and 1b , the operative circuits and components that achieve the basic function according to the invention may be discrete switching stages or blocks , but preferably some or all of them are combined so as to occupy suitable regions of program - controlled digital systems , or in other words microprocessors , computers and the like . thus the exemplary embodiments of the invention discussed below will serve merely to explain the basic function and mode of operation of the invention and do not restrict it to the particular embodiments shown . adjusting cylinders 1a , 1b are provided , which by imposition of a suitable ( pneumatic or hydraulic ) pressure medium put the traction - improving systems into operation directly . detailed explanation of these systems can be dispensed with , because the publications mentioned above can be referred to , namely the bosch publication mentioned above for the use of a gravel spreader as shown herein by fig4 a , and 4b as a traction - improving system , and the article in nutzfahrzeug for the general embodiment of a special chain system . the adjusting cylinders 1a and 1b therefore either directly activate shafts or rotary slides in the vicinity of the gravel spreader , and thus may for example be embodied as a gravel spreader , as shown in fig1 of the bosch publication , or by the actuation of suitable lever systems from the mechanical outlet of each adjusting cylinder 1a , 1b they bring about the deployment of special chains at the applicable wheels of the vehicle . to provide further detail on this point , how this works is that extra wheels , provided with sets of chains , are pressed against the sides of the tires of the driven wheels , for instance via a lever system as shown in fig2 a , and 2b or a rack and spindle drive as shown in fig3 a , and 3b , by the terminal elements , here preferably embodied as pneumatic adjusting cylinders 1a , 1b ; this simultaneously causes these wheels carrying the sets of chains to rotate , and the sets of chains are centrifugally thrown under the tire treads of those wheels of the motor vehicle . alternatively , or in addition , the gravel spreader can be used as a second traction - promoting system ; in that case , via rotary slides , the pneumatic adjusting cylinders 1a , 1b open the drain openings of gravel bins mounted ahead of the driven wheels and spread gravel over the road to the width of the tires . fig1 , 3 , and 4 show a pressure supply source 10 , which supplies the pressure , stored in it and kept at predetermined , preferably constant values , of the ( pneumatic ) pressure medium to a traction control or asr valve 4 , known per se ; for traction control , via its outputs 4a , 4b in a conventional manner , this valve 4 triggers suitable brake cylinders or preceding components 11 of the wheels at which spinning has been detected , for instance by abs sensors 20 , during starting or while driving . the triggering of the asr valve , which may be embodied as a double - acting valve , is effected via electrical signal lines 4c , 4d by a suitably embodied asr control unit or by a computer , in which certain parts of the program region are occupied for the sake of achieving traction control . the triggering may also be effected by a combined abs / asr control unit . it can be seen that upon activation of the asr valve , not only are the wheel brake cylinders finally supplied with pressure medium from the pressure source 10 , but via pressure medium lines 12a , 12b leading on to the adjusting cylinders 1a , 1b , these cylinders are acted upon by the pressure medium as well , so that a corresponding activation of the traction - promoting systems connected to or controlled by the asr valve is effected . in an advantageous embodiment , throttles 2 are incorporated into the lines 12a , 12b and provide for a time lag in the triggering of the adjusting cylinders 1a , 1b , so that brief or transient asr demands are filtered out , and the traction - promoting systems are not switched on unnecessarily , which with a gravel spreader for instance could empty it quickly . in the alternative embodiments shown in fig1 a , 2a , 3a , and 4a for activation of the traction - promoting systems via the adjusting cylinders 1a , 1b , separate electromagnetic valves 3a , 3b are provided , the pressure inlets of which are connected , via a branch line 13 with further branches 13a , 13b , directly to the line from the pressure supply source 10 , still upstream of the asr valve . the triggering of the electromagnetic valves 3a , 3b is effected parallel to the asr valve , in that its electrical signal lines are connected on either side via branch lines 14a , 14b to the corresponding electromagnetic valves 3a , 3b . in this embodiment , it is possible , via a double switch 5 connected via the electrical trigger lines 14a , 14b , to completely interrupt the delivery of the asr signals to the electromagnetic valves 3a , 3b , so that the supply of pressure medium to the adjusting cylinders 1a , 1b is prevented under driving conditions in which the use of traction improving systems is not at all necessary , such as when there is a firm surface or under other than wintry road conditions . finally , in the embodiments shown in fig1 b , 2b , 3b , and 4b it is possible for the electromagnetic valves 3a , 3b , which supply the adjusting cylinders 1a , 1b with pressure medium from the supply 10 via the throttles 2 , to be connected directly to the abs / asr control unit for electrical triggering , once again with the interposition of the ( double ) interrupter switch 5 . any of the features shown or described herein may be essential to the invention either singly or in any desired combination with one another . the foregoing relates to preferred exemplary embodiments of the invention , it being understood that other variants and embodiments thereof are possible within the spirit and cope of the invention , the latter being defined by the appended claims .