One of my coworkers just took part in the soap box derby in Portland, OR last weekend. My kids went and watched the thing.
those are some serious box carts.
Back in the days, we used a piece a wood (2x12). Nailed a 2x4 to make a fixed rear axle. Another 2x4 for the front axle fastened with a single 6' nail (or if we were fancy, a machine screw, nut and washers) to allow the front axle to pivot.
For wheels, we used ball bearings assemblies. We whittled each end of the front and rear axles to match the inner diameter of the bearing assembly and forced the "wheel" onto the axle. Then shims and nails to keep the bearing from sliding off. Yes, the wheel was metal on road.
For brakes, we used our father old shoes and hammered the toe of each shoe to either side of the front axle. Adjacent to each shoe, we attached the end of a singe piece of rope. By grasping the rope in both hands, we could pull the front axle to the right or left to steer. We would stick our feet into the oversized shoes and to brake, we would press down and jam the shoes to the street.
So here is the bill of materials
1 piece 2"x12"x48" wood (body)
1 piece of 2"x4"x36" wood (rear axle)
1 piece of 2"x4"x24" wood (front axle)
1 pair of shoes (brakes)
4 ball bearing assemblies (front and rear wheels)
1 piece of rope for steering
nails to fasten axles to body
and a spotters at the bottom of the hill to give the all clear before you let gravity take you down the hill. We used to use two roads off La Horquette Valley Road in Glenco as our tracks.
Very similar to the illustration above except for the body design and the use of two wheels on the front axle instead of one.