Extending the Lifespan of Tires

By

Shmuel L. Weissman and Jerome L. Sackman

Symplectic Engineering Corporation

and

David Gillen and Carl L. Monismith

Institute for Transportation Studies

University of California, Berkeley

Overview

• Motivation

• Factors contributing to tire life

• Proposed strategies

Motivation (Cont.)

Extending the lifespan of tires:is the best approach from an environmental

standpoint.is the largest contributor to reducing the

number of scrap tires.Problem: Tire life increase is leveling off.Objective: Identify ways to extend tire life

Factors Contributing to the Average Lifespan of Tires

• Maintenance

• Original Equipment (OE) tires

• Road condition and design

• High performance tires

• Budget tires

Tire Maintenance

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

92 93 94 95 96 97 98

Inspection YearNormal Wear Nothing Observed Abnormal Wear

Road Hazard Separation and Oxidation Other

Normal Wear: ~19% of removals

Abnormal Wear: ~50% of removals

Nothing Observed: ~9% of removals

Road Hazard: ~11% of removals

Oxidation and Separation: ~10% of removalsOther: ~1% of removals

Causes for discarding tires (Source: Michelin).

Tire Maintenance

• Alignment

• Rotation

• Tire inflation pressure

Tire Inflation Pressure

“Under-inflation is tire’s #1 Enemy.” (Source: RMA)

“Air pressure - Nothing else is more important.” (Source: Michelin)

“Improper inflation pressure may result in rapid or irregular wear.” (Source: Bridgestone-Firestone)

Tire Inflation Pressure (Cont.)

• National Highway and Traffic Safety Administration (NHTSA) survey found that, on average, tires are inflated to 6.1 psi below placard.

• NHTSA compared hot pressure to placard, which is intended as cold pressure.

Tires are actually inflated, on average, ≈10 psi below placard.

Tire Inflation Pressure (Cont.)

• For each psi below placard, tires lose 1.78% of their tread life (Source: Goodyear).

• Example: a tire with an 80K-mile limited warranty, maintained at 10 psi below placard, would lose 14K miles of its tread life.

Proposed Strategies

1. Technology: Auto-inflate systems

2. Public education

3. Corporate average tire life

4. Ad-valorem tire disposal tax/rebate

Strategy 2: Public Education

Educate the public to:

1. Better maintain its tires

2. Purchase longer life tires

Strategy 2 (Cont.)

• Advantages– Relatively inexpensive– Little opposition (both RMA and car producers

advocate proper tire maintenance)– Addresses existing vehicles

• Disadvantages– Not very effective in extending the average life

mileage of tires (NHTSA survey results)

Strategy 2 (Cont.)Contribution to extending tire life

Year

California population (Millions)

Estimated tires generated IWMB Data (millions)

New Level of Tires Generated

Tires Imported (millions)

Total PTEs (IWMB Data)

NEW Total PTEs (IWMB Data)

Reduction in Total PTEs Generated (millions)

2001 34.8 33.300 33.30 1.70 35.00 35.00 0.002002 35.8 34.835 34.50 2.00 36.84 36.50 0.342003 36.4 35.668 35.32 2.00 37.67 37.32 0.352004 36.9 36.425 36.06 2.00 38.42 38.06 0.362005 37.4 37.203 36.84 2.00 39.20 38.84 0.372006 37.8 37.904 37.53 2.00 39.90 39.53 0.382007 38.4 38.830 38.45 2.00 40.83 40.45 0.382008 38.9 39.681 39.29 2.00 41.68 41.29 0.392009 39.4 40.559 40.16 2.00 42.56 42.16 0.402010 40.0 41.570 41.16 2.00 43.57 43.16 0.412011 40.4 42.403 41.98 2.00 44.40 43.98 0.422012 40.9 43.372 42.94 2.00 45.37 44.94 0.43

Strategy 2 (Cont.)

• Present value of benefit: $1.6B

• 5% probability of meeting or exceeding the projected benefit.

• Conclusion: should be pursued, but in conjunction with other strategies.

Strategy 1: Technology: Auto-Inflate Systems

• Concept: automatically maintain air pressure at placard level (adjusted for temperature).

• Assumption: Introduced only as OE with new vehicles.

Strategy 1 (Cont.)

• Advantages– A reliable way to maintain proper tire pressure

– Maximize tire life

– Improves safety

– Improves fuel economy

– Reduces air pollution

– Applicable to both light and heavy-duty vehicles

Strategy 1 (Cont.)

• Disadvantages– Increases the upfront cost of new vehicles– Requires maintenance (e.g., replacing batteries

every 10 years)– Automakers may oppose (the Alliance of

automakers lobbied strongly to allow indirect TPMSs in the NHTSA rule)

Strategy 1 (Cont.)

Contribution to extending tire life

Year

California population (Millions)

Estimated tires generated IWMB Data (millions)

New Level of Tires Generated

Tires Imported (millions)

Total PTEs (IWMB Data)

NEW Total PTEs (IWMB Data)

Reduction in Total PTEs Generated (millions)

2001 34.8 33.300 33.30 1.70 35.00 35.00 0.002002 35.8 34.835 33.58 2.00 36.84 35.58 1.252003 36.4 35.668 34.36 2.00 37.67 36.36 1.312004 36.9 36.425 35.08 2.00 38.42 37.08 1.342005 37.4 37.203 35.83 2.00 39.20 37.83 1.372006 37.8 37.904 36.50 2.00 39.90 38.50 1.402007 38.4 38.830 37.40 2.00 40.83 39.40 1.432008 38.9 39.681 38.22 2.00 41.68 40.22 1.462009 39.4 40.559 39.06 2.00 42.56 41.06 1.492010 40.0 41.570 40.04 2.00 43.57 42.04 1.532011 40.4 42.403 40.84 2.00 44.40 42.84 1.572012 40.9 43.372 41.77 2.00 45.37 43.77 1.60

Strategy 1 (Cont.)• Benefit/Cost ratio: 1.24• Net present value: a profit of $1B• 60% probability of meeting or exceeding the

projected NPV.• Conclusion: Highly effective and reliable strategy

that also improves safety and fuel-efficiency, and reduces air pollution.

Strategy 1 (Cont.)

Implementation options

1. Educating the public to demand auto-inflate systems with new vehicles

2. Mandating a phased-in introduction of auto-inflate systems in new vehicles over a number of years (similar to the TPMS rule)

• Thank you

• Questions?