Beginning from 1st April 2017 onwards all Indian car manufacturers will have to maintain an average fuel economy for the fleet of new vehicles they sell each year. This new regulation termed as CAFÉ (Corporate Average Fuel Economy) is in line with the existing standards in western countries. The current 2017-18 targets of 130 g/km is quite lenient and most of the manufacturers should meet it quite comfortably. However because it’s an average fuel economy, in order to sell big fuel inefficient SUV’s the vehicle manufacturer must also sell small fuel efficient cars. The vehicle manufacturer can be fined if their annual vehicle fleet doesn’t meet the set targets for the financial year 2017-18.
Impact of Rolling Resistance
Fuel economy is one of the most important buying factor for Indian customers. A tyre’s rolling resistance affects fuel economy. Rolling resistance is something that is a characteristic of a tyre and exhibits its importance while running in city and highway. Hence most of the car manufacturers are very focused on reducing the rolling resistance of the tyre. To meet the manufacturer’s demands, these tires are often designed with a priority on reducing weight and rolling resistance and are molded with slightly thinner sidewalls, shallower tread depths and use low rolling resistance constructions and tread compounds.
All car manufacturers in India test the vehicle in standard test conditions which could be different from the way we drive the vehicle in city or highway. Standard test conditions creates similarity and different vehicles can be compared. But how much influence does each of these elements have and when are their influences felt? Once you eliminate the fuel converted into heat by the engine, the relative percent of influence that these other factors represent during stop-and-go city driving are very different than during steady-speed, highway driving.
During stop-and-go city driving, it’s estimated that overcoming inertia is responsible for about 30% of the vehicle’s resistance. Driveline friction is about 40%, air drag is about 10% and tire rolling resistance is about 20%.
Impact of tyre pressure
The easiest way to reduce rolling resistance and enhance fuel economy is to make certain that the tires are properly inflated. A vehicle that requires its tires to be inflated to 35 psi (based on the vehicle’s tire placard) will have an increase in rolling resistance of approximately 12.5% if the tires are allowed to become under-inflated to just 28 psi. Therefore, maintaining the vehicle manufacturer’s pressure recommended for light load and heavy load conditions may almost be as important as the tires being used.