hiin cycle wheel inside the tyre rim is there and that has stokes. why that strokes ? why cant it be a complete disk? same in cars the disk has holes. why holes

there are many reasons for this.....the first and the most important one is cost efficiency...and then comes pressure,when airr passes easily between the rims there is no problem.but a complete disk offers more surface area for the air to collide and the cycle while moving at a high speed and taking a turn may topple down.......