This is often referred to as pushing, plowing, or refusing to turn in. The car is referred to as “tight” because it is stable and not something that wants to spin. It is a condition where the car responds slowly to the amount of steering wheel turn. If the car over responds to the steering wheel inputs then this action is called Oversteer.
Understeer determines the turning radius of the car. Lesser the under steer, sharper the turns that can be taken.
Unleaded petrol is manufactured without the addition of antiknock (a gasoline additive used to reduce engine knocking). The presence of antiknock in the petrol increases the octane rating and they are also harmful for the environment. The unleaded petrol therefore has less octane number and is mild on atmosphere. Cars fitted with catalytic converter uses unleaded fuel. Cars can be easily converted to run on unleaded petrol by changing the timing of the machine.
The use of unleaded petrol doesn't release harmful lead compounds into the atmosphere and is thus environment friendly.