The article presents the results of researches conducted with the use of computer that allow to estimate the influence of tractor unit parameters on possibility of self-excited oscillations of wheeled tractor frame in the case of its moving under load that causes significant slipping of driving wheels.

The method of computer calculation allowing to determine conditions of self-excited oscillations of frame in longitudinal plane is developed. It is applied in the case of moving of tractional wheeled vehicle on even surface with load that causes significant slipping of driving wheels.

Experimental results of flotation of GAZ-66-40, KamAZ-4350, Ural-4320-30 and Ural-5323-20 all-wheel drive vehicles on snowy wild land are given. Comparative assessment of flotation is carried out on basic indicators such as specific drawbar force, specific force of resistance to towing of car, maximal speed of rectilinear uniform motion without towed load and minimal car turning radius without flotation loss.