It is difficult not to notice the fact that the rear wheels of the tractor are almost always much larger than the front ones. Well, or the front wheels are much smaller than the rear ones - that's how you look at it. The question is different: such a difference in wheel diameters is clearly dictated not by "design delights", but by some kind of technical necessity. So why does a tractor need such a wheel shape and no other?
Large rear wheels and small front wheels on agricultural tractors are really not made for beauty. This shape and dimensions allow you to achieve several positive results at once. As you know, tractors have to travel a lot in rough terrain or in the absence of a solid road surface. In such places, there is always a high risk of getting stuck, skidding in place. In addition, dirt, sand, mud and snow are not the best "soil" under the wheels for driving pirouettes. All these problems are solved by the tractor wheels.
At first, large rear wheels with pronounced ground lugs are needed by the tractor in order to have good, reliable grip on the ground or snow and confidently wade over rough terrain. As is known, the contact patch between the tire and the ground increases not only by increasing the width of the wheel, but also by increasing its diameter. This is especially evident in the example of various all-terrain vehicles. Secondly, large wheels allow to increase the ground clearance in a natural way, which is also extremely useful for off-road vehicles.
ThirdlyLarge rear wheels make a huge difference in terms of torque. The bottom line is that the larger the wheel, the smoother the tractor under the influence of traction. At high torque, the tractor pulls away slowly, which protects it from slipping on rough terrain. At the same time, this arrangement of wheels also has its drawbacks: tractors have the custom of tipping over around the rear axle. Therefore, the tractor driver should always carefully monitor how the hitch of the trailer, plow or any other agricultural equipment is installed.
As for small front wheels, then they are also made in this form for a reason. The point is, the smaller the wheel, the easier it is to manipulate with the steering device. Turning with large wheels, especially outside the asphalt, would be very difficult. Therefore, to improve the maneuverability of tractors, the front axle is equipped with wheels of a smaller diameter. These are especially useful when driving in snow or mud.
If you want to know even more interesting things about cars, then you should read about why are Russian tanks still driving on engines 90 years old.