Unibody

Many new cars these days are "uni-frame", built as a one piece unit and so they have no chassis in the old sense. Older cars are built on a chassis.

Chassis

The chassis is usually a ladder-like construction of steel, usually the strongest part of the car. It is like the foundation of a house. In a house, everything rests on the foundation.

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Frame

The engine, the transmission, the various systems we have discussed, the exterior and the interior of the car are all bolted onto the chassis or onto parts that are in turn bolted onto the chassis. In uni-frame construction they are bolted directly onto the frame. The thing to know about the chassis is the importance of checking it if you are buying a used car. If a car has been in an accident the chassis or frame can get bent or cracked. This is very dangerous to drive. A car with a bent frame will not respond properly when steering and braking.

Exterior

The exterior of the car can be constructed of various materials, from heavy steel to light metal (known as tin cans) or even fiberglass. The heavier the material used, the stronger and safer in the event of a collision. On the other hand greater weight means more gas is consumed and the car is more expensive to run. Lighter materials have now been developed with more strength, but you will notice that the more expensive luxury cars are still constructed with heavy steel frames. An additional frame is often built these days around the passenger compartment and on some cars the outer frame is designed to deliberately collapse, thus absorbing some of the impact in the event of a collision. Of course the now collapsed car is not much use!

Decide for yourself what you want as far as safety and economy and choose your frame accordingly.