Why Slick tires?
The Trikke tires have a small diameter and have a round profile (not flat like a car). The resulting contact patch is the size of a quarter dollar coin. Also, Trikke is a cambering vehicle, which uses variable 90 degrees arch of contact.
The speed the vehicle travel is very slow and will not face aquaplaning issues. The torque on the wheels is very low and will not benefit from threads.
We have tested knobby and slick tires for the past 18 years, and the conclusion is that knobby offer an inferior traction on cornering, braking, slippery or wet terrain. Also the noise and vibration under your feet are very noticeable compared to the smoothness of the slick tires.
The slick tires proved to perform really well under all conditions, on and off road.
The consistency of the contact line enhances safety and traction at all conditions.