Impact of Wheel Design on Fuel Economy
There has always been an effort to manage wheel weight with respect to predetermined targets provided by the automotive OEM. The benefits of reducing un-sprung weight and the corresponding positive affect on noise, vibration, and performance are well known. However, there has been little effort in managing the distribution of the weight found within the wheel.
The wheel and tire assembly is a system of rotating masses that takes a greater amount of energy to accelerate due to a combination of translational and rotational forces required to get the assembly moving and keep it moving. The majority of the mass of a vehicle is accelerated on a linear force vector. A general rule of thumb has been:
100 lbs mass reduction = 1.5% fuel economy improvement
Wheels are subject to the forces of both linear mass and rotational mass. The location of mass with respect to the point of rotation becomes as important as the total mass itself.
Mass at the outer diameter (OD) of the wheel requires a greater amount of energy to accelerate than mass at the inner diameter (ID) or hub area. Alcoa accounts for this effect by designing wheels with respect to the rotational mass moment of inertia.
1 lb of rotational mass = 4 lbs of sprung weight.
Every wheel Alcoa designs is tracked and compared as a benchmark to assure the lowest rotational mass moment of inertia available within that design envelope. Alcoa wheels forged from one piece of 6061-T6 aluminum also provide a 20% strength advantage over comparable A356 cast wheels further allowing for optimized weight distribution. The increased strength of forged aluminum allows Alcoa to reduce weight (especially at the outer diameter) and provide fuel efficiency and economy by reducing the energy required to accelerate the wheel.
Alcoa also applies Department of Transportation (DOT) acceleration profiles to determine the amount of energy required to accelerate each wheel. While many publications have noted that the DOT acceleration profiles greatly under-predict the habits of the average driver (i.e.: aggressive acceleration and air conditioning usage), these are the best industry resources currently available. Look for more stringent testing results from DOT soon.
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DOT city acceleration profile.
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Alcoa combines all of this data to optimize city and highway fuel economy performance from each wheel design. In side by side comparisons, Alcoa has decreased the energy required to accelerate a forged wheel by as much as 17% compared to a cast counterpart with respect to the DOT city acceleration profile. Not only does a forged aluminum wheel offer ultimate strength and durability with design flexibility, but also provides the important benefits of weight savings, efficiency and fuel economy.
For more information please contact your Alcoa wheel expert or e-mail us at
www.AlcoaWheelNews.com.
During the recent World Congress, held on April 14th, SAE held a Detroit Section Meeting featuring the 2008 Dodge Challenger SRT8. The event was attended by over 900 current SAE members as they were entertained by key Chrysler personnel responsible for the launch of the new Challenger. Alcoa not only attended the event but sponsored an evening reception to pay tribute to the new Challenger and showcase the technology behind the 20” forged Alcoa aluminum wheels fitted to each SRT8 Challenger.
The Mid-American Truck Show, held in Louisville, Kentucky, has become the premier regional commercial vehicle and consumer event for Alcoa Wheel and Transportation Products. The three-day show offers the opportunity for Alcoa to showcase our latest products and new innovations to customers and end consumers.
For 2008, Alcoa took the opportunity to announce our 60th anniversary of inventing the forged aluminum wheel with various new product introductions and innovations. The Alcoa booth featured wheel and transportation products including Dura-Bright® technology, Dura Flange®, Wide Base, light truck wheel designs and a new Retro® wheel reflecting the design of the original 1948 wheel with today’s technology.
Alcoa also presented several light truck and SUV wheel lines including Classic, Pro Series and Adventure Series wheels while taking the opportunity to publicly showcase a new point-of-purchase display concept for a Dodge Mopar 20” wheel fitment soon to be available with Dura-Bright® technology. 
