That is the regen/braking feature of the PDS carts. You can change out (the chip/jump pin) and get 20 MPH out of it down hill the regen kicks in. If you have a volt meter wired in you will see the batteries area charging when going down hill. Ours is set up to slow down from 13 MPH to 10 MPH when you let off the pedal. I went with the hill chip because we have hills and kids riding on them.