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7. Effects of Nitrogen Tire Inflation on Canadian Long-haul Trucking

Effects of Nitrogen Tire Inflation on Canadian Long-haul Trucking

The analysis and conclusions contained in this case study are those of the authors alone and do not necessarily represent the point of view of the Government of Canada.

Organization
Drexan Corporation

Major Findings
The demonstration project showed that inflating truck tires with nitrogen results in 4 to 6% fuel economy and extends tire life.

Project Timeline
February 2006 to November 2006

Please note that some figures such as cost savings on fuel are based on data from the period that this project took place.

Introduction

Trucking is essential to freight transportation in North America. Proper tire inflation reduces fuel consumption and greenhouse gas (GHG) emissions, and laboratory and field-testing indicate that inflating new and retread tires with nitrogen results in greater fuel/emission savings and extends tire life. A well-known study, Million Mile Truck Tires published in 1985, was the first to identify the potential benefits of inflating truck tires with nitrogen.

Since tire rubber is more permeable to air than it is to nitrogen, tires inflated with compressed air deflate over four times faster than tires inflated with nitrogen. Deflation reduces fuel economy and increases rubber tread wear. In addition, the air and the associated water vapour that passes through the rubber, degrades the rubber and the steel belting, which shortens tire life.

Project Description

This project was undertaken with financial support from Transport Canada's Freight Sustainability Demonstration Program. Harris Transport Ltd. truck and semi-trailer tires were converted from compressed air to nitrogen inflated tires on a staggered basis between February and April 2006. The conversion to nitrogen inflation was done by West End Tire as part of normal tire maintenance at Harris Transport's Winnipeg depot. Tires were purged to atmospheric pressure and then inflated with nitrogen to set point pressure. The purity of the gas in the casing was verified using a hand-held oxygen analyzer, with a minimum purity of 95% nitrogen. Four tread depth readings were taken per tire with a hand-held electronic data collection system (Snapshot). Tread wear data was recorded during the test period as equipment cycled through the yard.

Drivers did not know which vehicles had nitrogen-filled tires and the routes travelled by trial and control groups were similar. Tires were converted to nitrogen at random, without regard for tire age or whether tires were new or retreaded. This way, any change in performance could be attributed only to the tire inflation gas.

Project Goals and Objectives

The purpose of this project was to prove that inflating tires with nitrogen not only saves on fuel and emissions, but extends tire life as well.

Project Methodology

Sensortracs, a truck-mounted system capable of tracking a wide range of information, recorded fuel consumption data in the test group. Fuel use was compared to baseline data that came from Harris Transport's fuel tax credit records.

The second set of data concerning tire wear also came from Sensortracs. Tire wear was compared to 2004 data based on tire pressure maintenance done by drivers and air-inflated tires. For 2005, the data was based on tire pressure maintenance done by a designated contractor and air-inflated tires.

By the end of the project period, 64% of the Harris fleet had been converted to nitrogen-inflated tires. They always tried to match trucks with nitrogen-inflated tires with semi-trailers similarly equipped. In rare instances where a truck with nitrogen-inflated tires was pulling a semi-trailer with air-inflated tires, the observed fuel efficiency of nitrogen-inflated tires would have been underestimated.

The control group was made up of trucks and semi-trailers with air-inflated tires and it, like the nitrogen-inflated test vehicles, was representative of Harris Transport's routes, payloads and operating equipment and, monitored by Sensortracs.

The baseline data for tread wear was taken from fleet records before the nitrogen inflation testing. During the project, tread wear was recorded for a sample of all tires, both nitrogen- and air-inflated.

Results

Fuel Economy

Figure 1 compares the seasonal fuel use during the trial period to two previous years of baseline data. The first sine wave (2004) shows fuel consumption per mile for a period when drivers maintained tire pressure and all tires were air-inflated. The shape of the curve shows the normal lower fuel economy in winter due to increased idling, lower engine efficiency and higher rolling resistance. The seasonal average was 4.58 mpg.

The second sine wave (2005) shows data for the period when a designated contractor was responsible for tire maintenance and all tires were air-inflated. The seasonal average was 4.66 mpg.

The third sine wave (2006) shows data for the nitrogen- and air-inflated tires during the project period. The seasonal average was 4.78 mpg based on 64% conversion of the fleet to nitrogen inflation.

When the results are prorated for 100% of the fleet, nitrogen inflation showed a 6.12% improvement over the 2004 data (air inflation and tire maintenance by drivers) and a 4.03% improvement over 2005 (air inflation and a designated tire maintenance contractor).

Figure 1: Fuel consumption comparison

Tread Wear
The tread wear assessment was based on over 110 million tread miles of data on 1,988 tire positions. Figure 2 shows tread wear for the nitrogen- and air-filled tires monitored in this project. It shows that, per 32^nd of an inch of tread wear, nitrogen-filled tires delivered about 50,000 km compared to 27,000 km for air-inflated tires. This means nitrogen inflation increased average tread life by about 85%.

Figure 2: Actual tire wear (new and retread casings)

Conclusion

This project proved that inflating tires with nitrogen and maintaining proper tire pressure reduces fuel consumption and GHG emissions while also increasing tire life. Comparing air-filled tires whose pressure was monitored and maintained by drivers or by contractors, yielded a fuel consumption reduction of 2.09% in favour of the tires maintained by contractors.

Nitrogen-filled tires reduced fuel consumption by 4.03% compared to air-filled tires (tire pressure for both maintained by a contractor). However, there is a 6.12% reduction in fuel consumption when using nitrogen-filled tires whose pressure is maintained by a contractor over air-filled tires whose pressure is maintained by the driver.

The trial determined that nitrogen increased tread life by 86% (new and retread casings).

Additional Information

• Summary of Report S4-85, Million Mile Truck Tires, Lawrence R. Sperburg
• Sensortracs (Presently unavailable)
• Harris Transport Ltd.
• Drexan Corporation
• West End Tire

Alternative Format

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PDF version (Size: 140 KB)

Date modified:

2011-11-07

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