Since you are a non-professional, there are many design parameters involved so I won’t go into details here.

It’s a very simple question. The reason why the front wheels protrude outwards is because they have to be equipped with brakes. , you need to leave space, do you understand this?

If the front wheel understands the rear wheel, you will understand half of it. In fact, the rear wheel in the double rear wheel is also protruding outward for the purpose of installing brakes. , the outer tire is concave inward because it facilitates the connection between the axle and the wheel, and because the connection point is on the vertical line between the center of the two wheels and the ground, it can ensure the balance of the wheel.

In this way I Draw a simple picture

This is a wheel with convex sides on both sides. The connection of the wheels must be like this [-[-frame-]-]

This is a convex side and a concave side. The wheels are connected like this][-frame-][

I found that there is no such concave and convex design. Not only is the structure compact, the center of the wheel is connected to the axle, and the wheels are rigidly connected to each other like a wheel. It maintains the balance of the wheels.

You want to ask why the above group is also rigidly connected?

You won’t understand this question if you explain it in depth. Simply put, forget it. When a single wheel rotates, the inner ring and outer ring of the wheel rotate at different speeds. Therefore, according to the design with protrusions on both sides, the outer wheel and the inner wheel will rotate at different speeds, which will reduce the strength of the axle and cause it to collapse. Twisted and deformed, causing hidden dangers to driving safety!