|Alcoa aluminum truck wheels vs. steel wheels (average use case). Source: Alcoa. Click to enlarge.|
Alcoa last week released the findings of a peer-reviewed life cycle assessment (LCA) which concluded that Alcoa aluminum wheels substantially cut the carbon footprint of commercial vehicles.
This analysis, performed by PE International and Five Winds Strategic Consulting, is the most comprehensive and transparent comparative LCA ever conducted on aluminum and steel truck wheels, according to Alcoa. It analyzed the entire “cradle-to-grave” production process of commercial vehicle wheels—from bauxite mining to wheel manufacturing, through a truck wheel’s use phase and end-of-life, including recycling and land filling. The study incorporated the latest available information on energy and material consumption, greenhouse gas emissions and other environmental releases.
The LCA was conducted based on a functional unit of “coupling truck tires to vehicle hubs” for an estimated wheel lifetime mileage of 1,000,000 miles under North American boundary conditions or 1,500,000 kilometers under European boundary conditions. Mass-restricted, volume-restricted, and average use case scenarios were evaluated.
Major findings of the study include:
Using aluminum wheels on an 18-wheel truck/trailer allows for a net cradle-to-grave reduction of 16.3 metric tons of CO2e emissions under North American boundary conditions. That means that substituting 18 conventional steel wheels by aluminum wheels with a weight advantage of 414 pounds saves 16.3 tons of CO2e over their total lifetime.
Under European boundary conditions, 13.3 tons of CO2e savings over the steel wheel baseline are achieved over the total wheel life cycle. The truck model for Europe employs 12 wheels with a total weight advantage of 474 pounds (251 kg), which is even higher than for the US scenario due to different wheel geometries.
The EU use phase savings in the average use case are nevertheless smaller than in the US since it is dominated by the mass-restricted results, which produce higher fuel savings per tonne-km for the US truck due to its lower fuel economy. However, the European scenario is not to be considered “worse” than the North American case as the total CO2e savings per wheel in Europe (1.11 tons CO2e) are actually greater than the savings per wheel in North America (0.93 tons CO2e).
The savings from switching one truck from steel wheels to forged aluminum wheels in the US average use case is approximately equal to the average annual carbon footprint of a four person household.
For volume-restricted vehicles in North America that are unable to add additional payload, switching from steel to Alcoa forged aluminum truck wheels produces an average lifetime savings of more than 520 gallons of fuel. In Europe, these savings amount to more than 1,942 liters.
While aluminum wheels require more energy to manufacture than steel wheels, the light weight and recyclability of aluminum allow for a net energy savings throughout the life cycle of an aluminum wheel. A truck with aluminum wheels can see a CO2 “break even mileage” as early as 205,000 miles, or about two years. Once this mileage is reached, all the travel on aluminum wheels produces CO2 and energy savings.
Alcoa wheels maintain their value throughout their lifetime and have an end-of-life scrap value that is nearly equal to that of primary aluminum.
Based on the above results and taking into consideration the rather conservative assumption about wheel lifetime and the negligence of rotational inertia effects on fuel economy, the use of Alcoa forged aluminum wheels over steel wheels can be seen as an active and highly efficient investment into the reduction of greenhouse gas emissions in the commercial vehicle sector.—“Comparative Life Cycle Assessment of Aluminum and Steel Truck Wheels”
Alcoa and PE International presented the findings of the LCA at the 12th Annual American Center for Life Cycle Assessment Conference in Tacoma, Washington on 25 September.