Green Tires 

Precipitated Silica in Tires: A Beneficial Combination

As fuel economy regulations tighten and consumer demand for green transportation increases, tire manufacturers worldwide are adding precipitated silica to tread formulations to improve fuel efficiency, eliminate greenhouse gas emissions and enhance tire performance and handling.

Reducing rolling resistance, or the amount of energy spent to move a vehicle, is an increasingly important solution to decreasing fuel consumption. In fact, tires are responsible for 20% to 30% of a vehicle’s fuel use.

Switching a majority of the reinforcing filler in passenger tire treads to a combination of precipitated silica—a synthetic form of silicon dioxide that is produced as a white powder or granule—and other materials can produce up to a 30% reduction in rolling resistance. This translates into a 6% increase in vehicle fuel efficiency that, if applied to just the U.S. passenger tire market, would save up to 8 billion gallons of fuel and $24 billion in fuel costs annually.

As much as 25% of the pollution generated by a vehicle is due to overcoming the rolling resistance of its tires. By adding precipitated silica to tire treads, an annual reduction of up to 45 million tons of carbon dioxide emissions could be achieved in the U.S. alone.

Silica also significantly improves a tire’s responsive handling and steering capability in a variety of adverse weather conditions. For example, silica-containing treads have been shown to offer as much as a 15% increase in wet adhesion—or grip—that is crucial for driver control of braking, cornering and handling. These tires also have been shown to improve traction on icy roads.

Historical Perspective

For decades, silicas have been used as part of the tire filler package to enhance adhesion and improve tear, flex fatigue and chip & chunk resistance. They typically weren’t used as a significant part of the filler package for the tread portion of the tire because they were harder to process, cost more and reduced treadwear. However, in the early 1990s, new products called highly dispersible silicas helped overcome some of these deficiencies.

The use of highly dispersible silicas in tire treads first took hold in the early 1990s in Europe due to higher energy costs, a better understanding of environmental effects and consumer appreciation for better handling and safety. Demand is now increasing in the United States due to many of the same reasons: rising energy costs, increased consumer awareness of environmental issues, tighter government regulations regarding fuel consumption and a desire for improved handling and safety.

California recently enacted a law requiring tire manufacturers to report the rolling resistance properties and fuel economy effects of replacement tires sold in the state to provide consumers with information about potential fuel savings. In addition, new U.S. corporate average fuel economy (CAFE) standards were signed into law in December 2007 requiring a 40% increase in the per-gallon fuel average for new domestic vehicles, including SUVs and small trucks, by 2020.

PPG Silica Products

Pioneering the development of synthetic precipitated silicas, PPG became one of the first manufacturers to bring them to market in 1937. In the 1970s, the company’s scientists showed the impact that the appropriate combination of silane, polymers and silca dispersion had on treadwear, traction and rolling resistance.

Today, PPG is a leading manufacturer of precipitated silica for the rubber, battery separator, carrier and coatings segment. It also offers a product line specifically for the tire market to enable tire manufacturers to optimize productivity, processability and tire performance.

Source material for the information contained in this backgrounder includes the following:

  • Tires and Passenger Vehicle Fuel Economy. Transportation Research Board Special Report 286, National Research Council of the National Academies, THE NATIONAL ACADEMIES PRESS , Washington, DC, 2006.
  • Myers, A, TDA Research, Inc., Final Scientific Report, Improved Fuel Efficiency from Nanocomposite Tire Tread, Report DE2006-875756, US Dept of Energy, Inventions & Innovation Program, 2005.
  • Senator Charles E. Schumer (July 22, 2005), New Fuel Efficient Tires Could Save Upstate New Yorkers $225 Million, Conserve Fuel, And Reduce U.S. Dependency On Foreign Oil – Schumer Introduces Amendment To Energy Bill.
  • Greene, D., DeCicco, J. Engineering-Economic Analyses of Automotive Fuel Economy Potential in the United States. Annual Review of Energy and the Environment, Vol. 25: 477-535 (volume publication date November 2000).
  • Hankook Tyres continues to increase awareness in the Australian market…, Copyright © 2003, http://www.hankooktyre.com.au/V2/news/ad_display_marketing.asp retrieved on 2007-11-12.
  • Assembly Bill (AB) 844 (Nation, Chapter 645, Statutes of 2003), California Fuel Efficient Tire Program and Proceeding (Docket # 02-FET-1), http://www.energy.ca.gov/transportation/ tire_efficiency/index.html retrieved 2007-11-12.
  • Tyres-Online (November 2000), The Benefits of Silica in Tyre Design, A Revolution in Tyre Technology, http://www.tyres-online.co.uk/technology/silica.asp retrieved on 2007-11-12
  • Friedrich, A Fuel savings potential from low rolling- resistance tires, www.energy.ca.gov/ transportation/tire_efficiency/documents/2002-09-19_workshop/FRIEDRICH_FUEL _SAVINGS.PPT retrieved 2007-11-12.
  • Edsall, L. Michelin intensifies tyre r&d efforts, European Rubber Journal, August 1, 2005.
  • Goodyear Ice Tire and European Ultra Grip 5 Brrrrring Kudos, Goodyear Press Release, 11/02/1999, http://www.goodyear.com/media/pr/pr_1999/21941ti.html retrieved 2007-11-12.
  • Wagner, M. P. Reinforcing silicas and silicates. Rubber Chemistry and Technology (1976), 49(3), 703-74.