main critique really is there cropped a bit tight, 1st pic you have clipped his helmet. second shot being a jump id would tend to have more space under the wheels rather than the biggest space above the rider, 3rd pic is the best of the bunch, 4th a bit tight to the left. Try shooting a bit wider then can crop to suit, also try shooting some landscape shots rather than portrait as that will allow more space especially for the cornering shots..
good effort though