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Ultra-light low-drag autos

The innovation key to transform the auto industry will be a shift to ultralight but ultrastrong auto-bodies, made of advanced materials. Not only will these bodies be simpler and cheaper to manufacture, they will also trigger snowballing weight savings. With drastically lighter platforms, propulsion systems can be smaller, lighter, cheaper, more efficient, and, for autos, electrified.

Some improvements in automotive fitness are so straightforward with existing technology that they are considered the industry’s quickest win. Achieving vehicle “fitness”—designing out weight, aerodynamic drag, and rolling resistance could together boost fuel economy by 50% with no electrification. But, it captures only a part of the prize, and automakers can go much further to capture competitive advantage and get us off oil

Explore Ultra-light low-drag vehicles further with the information below from the Reinventing Fire portion of the Knowledge Center.

Examples of carbon composite structures

The carbon fiber manufacturing market is very concentrated; six companies produce nearly 93% of the world’s supply of carbon fiber.


Basic characteristics of Revolutionary Plus autos

Our Revolutionary auto class is based on RMI’s extensive work on the Hypercar. We use a cost model for superefficient battery-electric and fuel cell autos for both cars and light trucks. These vehicles, described in this table, are designed to compete with EIA’s average automobile in price and all driver attributes.

Sales-weighted curb mass and density of new autos sold in U.S., 1986–2009

Autos in the U.S. have increased in weight by 16% since 1986 to an average of 3,533 lb. in 2009. Cars have also gotten denser, rising 14%—from 28 to 32 lb per interior cubic foot. Yet since 1986, U.S. adults got only 8% heavier.

Advanced composite energy absorption vs. other materials

Composites have dramatically improved energy absorption over both steel and aluminum. Composite-based crush cones and similar structures built into autobodies can absorb 120, even up to 240, kJ/kg, vs. about 20 for steel. Crush properties can also be optimized by mixing costlier carbon fiber with cheaper materials like fiberglass.

Comparison of carbon fiber vs steel manufacturing costs

Automotive manufacturing costs can be cut by 80% with carbon fiber-based autos vs. steel-based ones due to greatly reduced tooling and simpler assembly and joining. However, such cost savings are currently overshadowed with carbon fiber material prices upwards of $16/lb.

Traffic fatalities, vehicle weight changes, and vehicle size, based on 1999 U.S. fleet on the road

Crash-safety risk with lightweight materials in automotive applications is only perceived, not supported by evidence. Lighter autos are actually safer than heavier ones the same size.


Power to accelerate 0–60 mph in 9 seconds

Every 10% decrease in an auto’s weight can raise fuel economy by roughly 6%.



Vehicle retail price and curb weight, new U.S. car sales, model year 2010

Lightweight autos needn’t cost more. The MY 2010 U.S. new-car fleet shows little or no correlation between lighter weight and higher prices.



Tractive load formulas

Powertrain efficiency from tank to wheels can't exceed 1.0, and is around 0.17 in a typical modern car or 0.35 in a good "full hybrid," but the energy needed to move the car can be reduced severalfold by making it lighter and more slippery.


Energy flow through a typical internal combustion engine drivetrain

This chart shows why less than 0.5% of the energy in a typical modern auto’s fuel actually moves the driver, and only 5–6% moves the auto. An auto's weight is responsible for more than two-thirds of the energy needed to move it. All told, 86% of the fuel energy never reaches the wheels.

How to make advanced composite hypercar class autobodies

The Hypercar (shown) achieved 53% curb-mass reduction without compromising safety. Its 14-part structure was much simpler than its typical 100–200 part counterparts made of steel and aluminum. A paper by Oak Ridge National Laboratory drafted a concept of a composite intensive body-in-white with 18 parts.

Carbon fiber precursor basics

Raw carbon fiber is made from either polyacrylonitrile (PAN) or a petroleum pitch precursor. Rayon was used prior to the development of PAN. These fossil-fuel-based materials come from petroleum refining or natural gas processing.


Tire price and rolling resistance coefficient

It costs little or no more to purchase tires with dramatically improved rolling resistance. Going from the least to most efficient tires improves fuel economy by over 8%.


Carbon fiber market share by company

The carbon fiber manufacturing market is very concentrated; six companies produce nearly 93% of the world’s supply of carbon fiber.


Carbon fiber cost breakdown

Carbon fiber costs are primarily driven by manufacturing. Within the manufacturing process, petroleum-based precursors account for just over half the cost of carbon fiber. Across the industry, manufacturing costs are dominated by the high cost of carbon fiber precursor materials.


Horsepower to overcome aerodynamic drag

Each 10% decrease in an auto’s aerodynamic drag can raise its fuel economy by very roughly 3%.

Easing the Pain at the Pump

While increased domestic oil production may mitigate national security
issues, it does little to ease the pain at the pump— US oil reserves are considerably more expensive to extract than reserves from the Middle East or Venezuela.[3] In addition, these supply-side solutions are only a finger in the leaky dam of our addiction to oil. Instead of trying to produce more, we should focus on using less through the efficient use of energy—starting with transportation since it drives the majority of US oil demand.

Size Matters

Strong but lightweight materials such as aluminum (able to absorb about twice as much crash energy per pound than steel) or carbon fiber (only 1/3 the density of steel but able to absorb up to six times more crash energy than aluminum) enhance safety and reduce vehicle weight.

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