four feet of clearance, and they also now have fiberglass bodies that attach to the chassis separately and are designed to be easily removed and easily replaced when damaged. The use of fiberglass panel bodies has allowed monster truck owners to develop a wide variety of thematic concept trucks that scarcely resemble the modified stock trucks that became early monster trucks. Engines are now typically mounted behind the driver on most trucks and are typically supercharged, run on a methanol-based fuel, and have displacement of up to 575 cubic inches (9.42 L). Axles are mostly taken from either heavy-duty military trucks or road vehicles such as school buses, and are modified to have a planetary gear reduction at the hub to help turn the tires. All trucks have hydraulic steering in both the front and the rear (four wheel steering), with the front wheels controlled by the steering wheel and the rear wheels by a toggle switch. The tires are typically "terra" tires used on farm equipment, and are of size 66-inch in diameter, 43-inch in width, and fit on 25-inch diameter rims (168×109–63 cm). Most trucks utilize a modified or custom-designed automatic transmission, such as a Turbo 400, Powerglide, Ford C6 transmission, or a TorqueFlite 727. A limited number of trucks utilize a Lenco transmission, which traces its roots to drag racing. Most of the automatic transmissions are heavily modified with transbrakes, manual valve bodies, and heavy duty gear sets. Trucks running a Lenco use a centrifugal clutch as opposed to a torque converter, which are used in automatic transmissions. Lenco transmissions are usually found in two-speed or three speed configurations, and are commonly shifted using compressed carbon dioxide. The trucks have many safety features, several of which are required just to run in the indoor arenas that the trucks frequent. Trucks are equipped with three shut-off switches: a remote ignition interrupt (RII), which allows event stewards to stop a truck remotely, a switch within the driver's reach in the cab, and another at the rear of the truck so that all electrical power may be shut off in the event of a rollover. Many trucks are constructed with the driver sitting in the center of the cab for visibility. Most cabs are shielded with Lexan or comparable polycarbonate, which not only protects the driver from track debris, but also allows for increased visibility. Drivers are required to wear