In recent years, increased attention has been paid abroad by manufacturers of tractor equipment and its buyers from Russia to universal wheel-wheel-drive tractors of high power with a classic 4K4a layout with smaller front wheels than rear wheels.
The development of this layout has led to an increase in the role of the front axle due to an increase in the weight of the tractor attributable to it (from 25 … 35% previously to 35 … 40% at present), the use of tires of the front wheels of increased size to improve traction. Tractors of such a layout scheme provide good maneuverability of the machine-tractor unit with minimum angular and linear oscillations of the skeleton, have sufficient agrotechnical and ground clearance and protective zones necessary when processing row crops. In general, for the intended purpose, they are arable-tilled and can be effectively combined with both general-purpose implements (plows, stubble plows, cultivators for continuous tillage, etc.), and with implements and machines for inter-row cultivation of tilled crops (cultivators, thinners of crops and etc.), work with seed drills, fertilizer spreaders, trailers, various combined machines, including those that are hung in front, etc.
Compared, for example, with wheeled all-wheel drive tractors of non-traditional 4K4b ‘layout (with articulated frame) of similar power to them, wheeled tractors of 4K4a scheme are less material-intensive, more versatile and use these qualities in increased demand, and their maneuverability on average differs little from maneuverability tractors layout 4K4b ‘.
The share of 4K4a tractors among the wheel tractors of various layouts (classic with rear 4K2 drive axle, integral with front and rear identical driving wheels and 4K4b cab centrally located between the axles, as well as 4K4b mentioned) is now more than 90%.
The most effective use of wheeled tractors of high power 4K4a (over 280 hp) at work in the unit with energy-intensive, fully loading them with wide-gripping high-performance agricultural machine-tools in large areas with traction forces on the hook corresponding to the 3rd … 4th traction classes.
The leading manufacturers of Case IH, Fendt, John Deere, Massey Ferguson, New Holland and Valtra offered in the markets of the EU and North American countries are ten high-capacity 4K4a tractor models in the range 280… 335 hp, grouped by power and weight, are presented in tabl. 1. It can be seen that the upper power limit of modern high-power 4K4a wheeled tractors is shifted to the level of 335 hp, and samples of tractors of this scheme (from Massey Ferguson and Valtra firms) with even higher power — up to 340 … 370 and 354 … 370 hp respectively, prepared for serial production and demonstrated at the Agrosalon-2008 international exhibition.