I have seen a lot of different formulas about the forces acting on a wheel. So now I don't know what to use. So, I have a vehicule with 4 wheels ( Ø 200 x 50mm) with a load of 900KG. I want to know 3 things: 1. What power I need to start the vehicle to move. 2. What power I need for constant speed 6km/h? The rolling resistance. 3. What force ( pressure) the wheel gives on the floor? When the wheel stand still and when the wheel is rolling? In N/mm². The wheelcore is made in cast iron and the tread is polyurethane 92 shore A. Tread can be Rubber 68 shore A. The wheel can also be completely made in polyamide 72 shore D. The floor can be concrete, wood, linoleum. What are the influences when we double the wheels? What are the influences when we increase the diameter by 2? I'm almost sure it's impossible to calculate this. But, I'm satisfied when I have a good 'direction'.