Rolling resistance will use a classification from best performance (green category "A") through to the worst performance (red category "G") – category "D" is not being used.
Rolling resistance is the main key factor in measuring the energy efficiency of a tyre. It has direct influence on the fuel consumption of a vehicle. Fuel efficiency is important to reduce both CO2 emissions and the cost of driving.
The difference between each category means a reduction or increase in fuel consumption of between 2.5%-4.5%. That's a difference of about 0.42-0.56 mpg for a 36 mpg car per category.
This figure will increase even more for light and heavy trucks.