An estimated 93.5% of motorists in the EU are driving on under-inflated tires and causing an additional 18.4 million tons of carbon dioxide to be released into the environment, according to a recent analysis by Bridgestone Europe. That works out to an extra 6.9 g CO2/km for every car on Europe’s roads.
Based on the data collected in 2006, Bridgestone also estimates that 40% of vehicles consume an additional 2.8% in fuel due to their under-inflated tires, wasting 8.1 billion liters (2.14 billion gallons US) of fuel every year.
To collect data for the study, Bridgestone conducted free safety checks on 20,300 passenger cars in 19 EU countries during 2006. Only 6.5% of motorists had all tires correctly inflated, 54% had some degree of low inflation and 39.5% had at least one tire significantly under inflated (<1.5 bar or 21.8 psi). 12.0% of cars (1 in 8) were in danger of tire failure.
The free check-ups were conducted by Bridgestone at shopping centres and public car parks. They form part of the “Think Before You Drive” safety education campaign, a worldwide joint initiative between the FIA Foundation (Fédération Internationale de l’Automobile), Bridgestone Corporation and national motoring clubs, launched in 2005.
These results suggest that many motorists are unaware that a tire loses pressure naturally over time, like a balloon, and that driving on incorrect pressure can be dangerous. The loss of handling control and increase in vehicle drift rises sharply as tire pressure is reduced. Low tire pressure also has an extremely negative effect on tire durability, due to excessive shear stress in the shoulder and heat build-up from sidewall bending. The 12% of motorists identified with seriously low tire pressure face possible tire failure due to these factors.
The wear life of a passenger car tire is halved if pressure falls from 2.2 bars (32 psi) to 1.0 bar (14.5 psi). Based on this 2006 survey, Bridgestone’s Technical Centre Europe calculates that the almost 40% of motorists at risk are losing 19.3% of tire wear life—an average of 9,700 km or 9 months of tire usage (based on an average wear life of 50,000 km and annual mileage of 13,600 km).
A further 54% of vehicles are losing 5.2% of tire wear life; an average of 2,500 km or 2 months of tire usage. Adding these two groups together shows that 24.5% of tire wear is being lost through under-inflation in Europe.
Inflation pressure has a strong influence on tire rolling resistance, which is itself a key factor in determining vehicle fuel consumption. Depending on the type of road and driving style, rolling resistance represents 18% to 26% of the total force on a vehicle. Since low inflation increases rolling resistance, it has a direct effect on vehicle fuel efficiency and emissions.
Tire pressure sensors are one mechanism the EU is exploring in bridging the gap between the 130 g/km CO2 target and the 120 g/km per vehicle goal in upcoming legislation mandating CO2 limits. (Earlier post.)