Insructables user murphtron writes:

My son started riding a 16″ bike at 4 years old without training wheels. (He was first on a push bike without training wheels or pedals at about 3 1/2.) One day he decided to build a jump in the back yard. So he found a piece of 2 x 12 ramp (with random lumber laying around) and piled up some logs. He discovered it was a bit tricky to ride in the grass and hit his narrow ramp. So I said, ‘hey, let’s go in the street (dead end) and try this.’ First one brick was used to provide vertical lift, and then a second brick. He loved it.

With two bricks, the ramp becomes a bit wobbly. Plus, a 2 x 12 is a bit narrow, and a few times he rode off the ramp’s side. So I decided to build a jump with the following qualities:

  • Wider ramp
  • Adjustable height, so it will last for a few years as he grows
  • Portable, so I could drag it to the dead end or local schoolyard playground.
  • Safer (while still providing ample opportunity for skinned elbows and broken bones)