Undersoil ripping action. It is hard to describe without a visual. Here goes.... Rolling tines enter the soil at about a 45 degree angle with the tip pointing towards the direction of movement. As the wheel rolls forward the tine goes from 45 degrees forward to 90 degrees or vertical in the soil. As the wheel continues forward the tine will exit at a 45 degree forward with the tip pointing in the reverse position. This action of the tine under the soil rips and fractures the soil making is loosen the tearing roots. Torn roots put off new growth and the fractured soil allows the plant growing room and breathing room. Oxygen and nutrients pass more easily into and gasses out of the soil. Hope this helps Consider that. Piston type aerators plunge straight in and out. They tend to copact the bottom of the hole and sides if it is wet.