eli5 Why tractors have unproportionally big rear wheels?
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Because if you had large front wheels that are very hard to turn, they will hit the frame and engine of a tractor. So a large rear wheel for traction and load and a small one in front so you can turn is common. You can see the same for lots of horse-drawn wagons.
The wheel is large because it spread out the loaf on the soft ground better and makes it easier to drive over uneven ground. For a tractor the load is usually on the back having large wheels there is an advantage.
There are back loader tractors where the large wheel is in front, The design is a regular design. It is the drive compartment that is reversed. The design is used for digging and material moving applications not plowing fields, The loo like [like this mode](https://sv.wikipedia.org/wiki/Baklastare#/media/Fil:Volvo_Back_Loader_1976_front_q.jpg) The rear wheels turn and the front are fixed
There is also an articulated tractor [like this](https://static.agriculture.com/styles/width_550/s3/image/2021/04/02/International%20Harvester%204366%20hero%20image.png) where the wheels are all large and equal size. The wheels are all fixed to the frame. It is the frame that is split between the model so the front and rear can point in a slightly different direction. Because the wheels are fixed you can have large both from and back.
You can make the very large for farming with multiple wheels at each spot [like this](https://www.rbauction.com/cms_assets/category_images/1502501470/1502501470_W_S.jpg)
Articulated tractors have to a large degree replaced the backloaded design for large loaders. They look soothing [like this](https://power-equip.com/wp-content/uploads/2016/08/WLO_L90H_3_W_14394_01_Right.jpg). The articulation can be seen and is just below the driver’s cabin.
The back-loaded design is still used today in skid-steer loaders [like this](https://en.wikipedia.org/wiki/Skid-steer_loader#/media/File:Bobcat_S650_skid_steer_loader_(15084521732).jpg) the right and left side wheels can run at a different speed, that’s how you steer them. In applications where you have size limitations, they have a clear advantage over articulated tractors
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