Why is the wheel not solid?
If it is car tires, due to fast speed, friction and heat a lot, coupled with a strong centrifugal force, tires easily torn apart, but shorter life expectancy. (There are special industries need this solid tires, but the application is too narrow, too far away from our lives, do not consider)
If the wheel is solid, then the person in the car will be a great beating
Because he wants to drive and ride people to bring comfort,
