Plastic fuel tanks are highly popular with designers. There are a number of reasons for this. In the first place, plastic tanks can be shaped in almost any way and made to fit perfectly alongside surrounding parts. Moreover, the production of plastic tanks is cheaper, because it does not involve complex welding seams, as do metal tanks. At the same time, plastic tanks are generally lighter in weight, which eases handling, whether for a motorcycle or a lawnmower. And last but not least, plastic doesn’t rust.
One small drawback
Plastic tanks do have one small drawback: They are not completely impermeable. While there is no danger of a puddle of gasoline accumulating under the vehicle, a plastic fuel tank is unable to prevent the slow escape of gasoline vapor. This phenomenon is known as permeation and is a result of the polymer’s macromolecular structure. It can lead to substantial amounts of hydrocarbons being released into the atmosphere.
This explains why the U.S. Environmental Protection Agency (EPA) has now lowered the maximum permissible permeation of fuel from plastic tanks in motorcycles and other small items of equipment with gasoline engines. The maximum limit now stands at 1.5 grams per square meter of tank interior surface per day (g/m²/d). The UN Economic Commission for Europe is expected to follow the EPA’s lead here and likewise substantially reduce the maximum limit for motorcycle fuel tanks made of plastic.