Spikes are used to make your enemy robot back up. This happens by having the white part of your spikes go under their light sensors. Not only this, but you can also leverage their wheels. By doing this, they now have less traction which makes it easier to push them off the board.

To clean your wheels and get better traction on the board.

Weight Blocks

To add more weight above your wheels for better traction. 

Consider using wide wheels for better traction like these ones.