which includes instructions to not ride on the sidewalk. Given that the laws regarding motorized scooters vary from state to state, the scooter sharing instructions can differ from the local law. Mechanics Wheels and tires Stand-up scooters may have solid tires, pneumatic tires with tubes, or tubeless pneumatic tires. There is variety within each kind; solids generally have a honeycomb structure of some sort, often surrounding a hard-plastic insert. Sizes vary between and usually, and scooters with larger are available, for both road and off-road use. There are some with unusually wide tires especially for off-road use. Most of them use a steel or aluminum split rim. Drive and transmissions The simplest drive mechanism of stand-up scooters is the electric direct drive, where the motor directly drives the rear wheel. Some electric scooters have two motors, one for each wheel. Brushless motors can be extremely efficient this way, especially when regenerative braking is implemented. A large proportion of newer so-called "e-scooters" are designed this way. When electric direct drive is not the rule, the simplest is the spindle drive, which puts an extension of the engine's output shaft, the spindle, in direct contact with the scooter's rear tire. To work correctly, the tire must have a clean, dry surface with which the spindle can effectively interact. Scooters with this type of direct transmission can be pull-started with the rear wheel off the ground, or "bump"-started by forcefully pushing them with the rear tire in contact with the ground. Simple chain reduction drives are also used to transfer energy to the rear wheel, generally incorporating a type of centrifugal clutch to allow the engine to idle independently. Belt reduction drives use the combination of wide flat "cog" belts and pulleys to transfer power to the rear wheel. Like chain drives, belt drives include a centrifugal clutch, but are more susceptible to breakage in off-road conditions. Suspension The suspension systems of stand-up scooters range from nothing at all, to simplistic spring based fork systems, to the complicated, dampened cam-link and C.I.D.L.I (Cantilevered Independent Dynamic Linkless Indespension) suspension mechanisms or a hybrid combination of wooden deck, coil spring, and dampers. Brakes Brake systems of kick scooters include disc brakes; magnetic brakes; and less efficient hydraulic brakes. Brakes can be placed on the front and/or back wheel(s). Many newer e-scooter models also have Kinetic Energy Regeneration System (KERS), which also acts as an electronic