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Project on Self-Inflating Tires

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
FPInnovation - Forest Engineering Research Institute of Canada Division

Major Findings
Using manufacturer-recommended (optimized) tire pressures reduced fuel use on poor gravel roads by 5.6% for empty trucks and 2.0% for loaded trucks.

Project Timeline
September 2005 to April 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

Transport creates about a quarter of Canada's greenhouse gases (GHG). Freight transport creates about 44% of that total. Transport Canada has several programs to help freight transporters reduce fuel use and reduce GHGs. One such program was the Freight Sustainability Development Program (FDSP). The Forest Engineering Research Institute of Canada, now known as FPInnovation, received FDSP funding to study the fuel and GHG reductions gained by using automatic tire pressure control systems (TPCS).

Correct tire pressure affects fuel economy and tire wear for all types of vehicles. For example, we know that vehicles operating on highways should maintain optimized tire pressures to save fuel and prolong tire life. However, those operating on unpaved roads, such as logging trucks, can save fuel by reducing tire inflation to suit road conditions.

Project Description

It is well-known that on paved surfaces, maintaining truck tire pressure at manufacturers' recommended levels saves fuel, reduces GHG emissions and extends tire life. However, that same tire pressure does not provide the best fuel economy for gravel or roads surfaced with native materials. As shown in Figure 1, lower tire pressures distribute loads over a larger area. In soft road conditions, the larger tire contact area results in using less fuel because of reduced wheel slip, rutting and rolling resistance. Rolling resistance is the force required to roll a loaded tire. Tire companies seek to reduce the rolling resistance of their tires to improve the gas mileage of vehicles using them.

Figure 1. Drive-axle tire pressure control system arrangement and tire contact area (11R22.5 tire loaded to 2100 kg)

A TPCS is made up of an operator interface computer and air supply plumbing between a valve control assembly and each tire. The system allows drivers to monitor and adjust tire pressure to suit load, speed and road surface conditions while driving. TPCS optimizes both truck and tire performance and reduces loading stress on a road. In fact, TPCS offers the possibility of further reducing cost, energy, and environmental impact because off-highway roads could be constructed with less aggregate (thinner base courses).

While pilot testing identified potential benefits of TPCS, this project measured fuel savings. It also examined the effect of a tire pressure-maintenance system (TPMS) on fuel consumption. TPMS monitors and automatically maintains (inflates) tires, but has no operator control interface and cannot be used to deflate tires. A TPMS consists of a regulator-based control assembly and airlines to draw air from the truck's compressed air system and direct it to the tires, as required, to maintain a set minimum tire inflation.

Project Goals and Objectives

FP Innovation wanted to test self-inflating tires on fleets of trucks to find out:

• how much fuel these tires could save, and
• how well the vehicles would run during the spring thaw, when the roads were damaged by continual freezing and thawing, and could support less weight.

FPInnovation had two secondary goals, which were to find out:

• how much longer tires could last using this system, and
• how many fewer tires would fail.

Project Methodology

The original plan was to compare fuel consumption of test vehicles equipped with TPCS or TPMS against control vehicles without them. However, because of differences in routes, loads and drivers, early results were not clear.

FPInnovation then developed a standard test to measure fuel use by loaded and unloaded trucks operating on many road conditions (pavement, good quality gravel, poor quality gravel and muddy native-surface) with different tire pressures. Testing took place in 2005 and 2006. Fuel consumption was measured by weighing the truck's portable fuel tank at the beginning and end of each test trip. Each trip was repeated three to five times to calculate the average amount of fuel used for each set of test variables.

Two forest-product companies, J. D. Irving, Ltd. and Tembec Industries Ltd., provided TPCS-equipped trucks for the test. A third forest-product company, Sunbury Transport Ltd., provided two TPMS-equipped truck and trailer units used for the highway hauling of wood chips. During the project, 36 trucks of various types, duties and load capabilities were equipped with TPCS and tested. These vehicles were typically used for hauling logs from harvest sites to mills on both logging roads and highways. In addition, 25 TPCS-equipped off-highway log trucks were tested under off-highway conditions only.

TPCS settings are typically programmed to tire manufacturer-recommended minimum and maximum inflations to ensure operating safety and optimize tire performance and life. These pressures are specific to the tire size, operating speed and tire load. Each TPCS setting also includes a maximum safe operating speed (extremely low pressures can only be used at slow speeds).

Results

A standard test procedure (SAE J1321) was used to test how effective TPCS was for trucks operated by Tembec Industries Inc. at its Huntsville operations. The results are in Table 1.

 Table 1 Fuel consumption matrix test results for Tembec test trucks

	Trucks Empty			Trucks Loaded
Road Type	TPCS Off	TPCS on (drive/trailer)	Fuel Savings	TPCS off	TPCS on	Fuel Savings
Pavement	100 psi	55 / 48 psi	-0.1%	N/A1	N/A1	N/A1
Good gravel	100 psi	55 / 45 psi	6.6%	100 psi	80 / 83 psi	2.4%
Poor gravel	100 psi	27 / 30 psi	5.6%	100 psi	80 / 83 psi	2.0%
Mud	100 psi	30 / 30 psi	14.5%	100 psi	55 / 55 psi	30.1%

¹The recommended inflation for travel at highway speed was comparable to 100 psi and did not warrant evaluation.

The results show that as road surface conditions deteriorate, using TPCS saved more fuel. For example, a fuel savings of 5.6% was realized for empty trucks operating on poor gravel roads. In some tests, trucks with higher tire pressures became stuck in muddy conditions. When this occurred, drivers were told not to try to force the truck to move. Instead, they simply reduced tire pressures. This created greater traction and the trucks were able to continue their runs.

FPInnovations developed a spreadsheet based on the results in Table 1. It allowed users to enter the annual distance travelled per truck, average fuel consumption, fleet size, fuel price and time spent on each of the four road types. These inputs were used to predict fuel savings, expressed in terms of fuel volume, cost and estimated fuel savings possible with TPCS and optimized tire pressures.

Testing of two TPMS-equipped vehicles travelling on-highway provided no conclusive evidence of fuel savings due to the small sample size and variability in driver styles. FP Innovations felt that more accurate testing of TPMS would be too costly given that the expected fuel savings benefit would be relatively small.

Conclusion

The project measured the fuel savings from using tire pressure-control systems (TPCS). Lowering tire pressure to increase mobility under soft road conditions reduced the energy needed to move test vehicles on gravel-surfaced and muddy roads. Fuel savings increased as road conditions deteriorated. For poor gravel roads, TPCS reduced the fuel consumption of unloaded trucks by 5.6% and loaded trucks by 2.2%, for a round-trip average reduction of 3.9%. TPCS provided several other benefits for forest product companies. These included the potential to increase payloads on soft roads; reduce road construction costs; and haul full payloads for a portion of the seasonal load restriction period, which reduces inventory size and associated costs.

Although the TPMS results were inconclusive, FPInnovations concluded that the real advantage of this system would be reduced tire maintenance costs, with fuel savings as smaller added benefit.

Additional Information

• FPInnovation - Forest Engineering Research Institute of Canada Division:

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Date modified:

2012-03-08

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