first used as a four-speed and now as a five-speed. Although the five-speed unit (usually air-shifted) is still used in ADRL and Mountain Motor Pro Stock Association and in air-shifted three-speed units in pro modified, NHRA pro stocks utilize Liberty or G-Force five-speed clutchless manual transmissions. Body NHRA pro stock racers use NHRA-approved carbon fiber bodies. Windows are manufactured from polycarbonate. Some have complained that the "stock" portion of "pro stock" is not really all that accurate anymore, because so little, if any, of the race cars' bodies have their origins in the respective manufacturers' factories. Chassis Pro stock chassis are welded 4130 chrome-molybdenum alloy steel tubing, with an integrated "funny-car style" cage around the driver that, combined with the safety restraints and helmet produce a very rigid and safe driving environment that was brought upon after a violent rollover crash suffered by Bob Glidden during the 1986 Commerce, GA, round. Suspension Pro stock cars are required to use automotive-type suspension systems. Since the 1970s, front suspensions have utilized MacPherson struts with control arms; for rear suspensions, the design of choice is a four-link suspension with coil over shock absorbers connected to a fixed rear axle. Both the front and rear shock absorbers can be adjusted automatically during the run by air circuits that are controlled by an electronic control unit. Brakes The primary means of slowing the cars from their top speeds of around 213 mph are the drogue parachutes. As cars have exceeded the 200 MPH barrier, two parachutes are required as NHRA mandates twin parachutes when speeds exceed that. The chutes utilize either springs or compressed air launchers to get the chutes into the air as fast as possible and to avoid the dead air behind the car. Four-wheel disc brakes made by aftermarket manufacturers are also used. The brakes have single calipers on the front and double calipers on the rear with carbon fiber rotors. Fuel The factory hot rods may use only racing fuel (octane rating: 118), which is tested and certified by chemical analysis at events with the sanctioning body's approval. Some organisations will mandate a specification fuel. The NHRA will mandate a specification Sunoco racing fuel, but it is unknown if the specification fuel will be unleaded racing fuels as they are in other classes of motorsport where they are official fuel, or allow alcohol in the official NHRA fuel (as has been