The base unit is the body of the scooter.  Generally it consists of a steel, aluminum, or composite frame with a fiberglass or composite floor to support the feet and batteries.  Some scooter bases include a shroud over the front wheel and drive head, giving the scooter a bullet-shaped appearance.  Certain scooter models also use the shroud to create a dashboard housing some of the instrumentation (such as a key lock for turning the scooter on and off and a battery-level indicator) for the scooter.  The base also includes the wheels and the drive train.  In some scooters, the seat post is part of the base.  The scooter’s maneuverability and its suitability for indoor or outdoor use largely depend on the characteristics of the base unit such as its turning radius, the size of its wheelbase, its ground clearance, and its overall dimensions.

The base unit also affects the comfort and safety of the rider.  When evaluating a scooter, it is important to be certain that the base can accommodate the user's needs.  The floor should provide enough space to comfortably support the feet at a natural angle, and the overall dimensions should permit the controls to be easily reached and manipulated.  Some manufacturers offer models with optional extended bases for tall people or shorter bases for small adults.  Some models also offer optional extended footrests for those who wear leg braces or who have difficulty bending their knees.

It is important to evaluate the base for safety features, including its overall stability.  A scooter should not tip easily during sharp turns or on inclines such as curb cuts (if the scooter is designed for outdoor use).  Anti-tip wheels should be included as part of the frame to help support and stabilize the scooter.  On front-wheel drive units, anti-tips are often located laterally just behind the front wheel because they generally lack the power for steep inclines.  Because most rear-wheel drive scooters are intended to negotiate more rugged terrain, they are usually equipped with rear anti-tips to support the scooter on hills.  Side anti-tip wheels are sometimes offered as options.  It should be noted that lateral anti-tippers may cause difficulties on curb cuts and ramps.

Some scooters can be disassembled into modular units for transport and storage.  Modular design may also allow the scooter to be converted from a 3-wheeled to a 4-wheeled model or from indoor to outdoor use.

Source: ABLEDATA Fact Sheet on Scooters