Generation 1: 1948-66
The characteristics of the car were simple. A strictly stock frame and body; doors strapped or bolted shut and seat belts required; and heavy-duty rear axles required to keep cars from flipping during the race.
Generation 2: 1967-80
The first overall modification of the car came for the 1967 season. The car had a stock body with a modified frame and modified chassis. Holman-Moody, Banjo Matthews and Hutchenson-Pagan built chassis for the teams.
Generation 3: 1981-91
In 1981 came a more race-centered series of vehicles. The wheel base was reduced to 110 inches; and NASCAR downsized cars to better resemble cars on the showroom floor, though body panels were still purchased through the manufacturers.
Generation 4: 1992-2006
NASCAR altered the look of the race car significantly in this generation. It had a highly modified body, leading teams to spend hours in the wind tunnel to gain an aero edge. The bumpers, nose and tail were composed of molded fiberglass based off production counterparts.
Generation 5: 2007-2012
The so-called Car of Tomorrow introduced a new era in car safety. It featured a common body and chassis for all manufacturers designed to reduce the need for track-specific race cars. It included a front splitter and rear wing to offer teams aero adjustment options.
Generation 6: 2013
The Generation 6 car marks the return of the showroom look, as seen with this 2013 Ford Fusion. Manufacturer-unique body panels are placed on the existing chassis. Enhanced body designs are built to more closely resemble the cars found in showrooms across the US and the design aims to put the stock back into stock-car racing.
Alan