34 projecting into gap 30 projection 34 ensures that the belt does not slip off the wheels as can be seen both in fig1 a and fig2 in this retracted configuration the belt extension assembly is confined to space 32 reference is now being made to fig3 a and 3b showing another embodiment of the invention similar to that shown in fig1 a 1d with the addition of an angular limiters 80 and 82 intended to limit the angular displacement of the belt stretching arms the traction configuration in fig3 a and 3b correspond to those of fig1 a and fig1 b and the same reference numerals as those used in fig1 a and 1b used herein as well to indicate the same components reference is now being made to fig4 a 4g showing a traction system in accordance with another embodiment of the invention in a variety of views and in different successive traction configuration reference is first being made to fig4 a showing a traction system generally designated 100 with a traction belt support 101 that includes two cooperating and coaxial support wheels 102 with a gap between them these two wheels 102 define between them a track belt stretching assembly confining space that houses a track belt extension assembly generally designated 104 some components.