Ultralight Hybrid Vehicles: Principles and Design

The paper presents a technical case for 'ultralight hybrid vehicles' (UHVs), asserting that fuel efficiency can be improved 3–4x over conventional cars without compromising marketability. It emphasizes that reducing tractive loads—through mass reduction, aerodynamic optimization, and low-rolling-resistance tires—is the most critical factor in making hybrid drivesystems cost-effective. Using the SIMPLEV model, the author demonstrates a design with a curb mass of 585 kg and a drag coefficient of 0.19 that achieves high fuel economy (up to 115 mpg on highways) and low emissions, while meeting strict performance criteria for acceleration and gradability.

• Whole-system engineering is necessary for commercial viability because optimizing parameters in isolation—such as focusing only on drivesystems or only on mass reduction—fails to capture the synergies required for superefficient vehicles.
• Tractive-load reduction is the most significant untapped opportunity for improving fuel economy and is a prerequisite for making hybrid drivesystems commercially viable.
• Hybrid-electric vehicles (HEVs) are superior to battery-electric vehicles (BEVs) for mass marketing because they avoid the 'snowball' effect where massive batteries increase the size, cost, and mass of all other vehicle components.
• Series hybrid drivesystems offer advantages over parallel hybrids and conventional vehicles by decoupling the auxiliary power unit (APU) from peak power requirements and vehicle speed, allowing the APU to operate at optimal efficiency.
• Recursive mass decompounding—where reducing the mass of one component allows for the downsizing of others—can lead to curb mass reductions of 45–55% or more, far exceeding standard industry multipliers.
• Advanced materials, particularly polymer composites, can reduce body-in-white (BIW) mass by 60–67% and provide specific crash-energy absorption two to five times that of steel, ensuring that lightweight vehicles can surpass current safety standards.
• Modeling of a proposed ultralight hybrid design (curb mass 585 kg, CD 0.19) indicates fuel economy of 105 mpg (FUDS) and 115 mpg (Highway), with emissions approximating the California Air Resource Board's Equivalent Zero Emission Vehicle requirements.

APA

Moore, T. C. (1996). Ultralight Hybrid Vehicles: Principles and Design. RMI. https://rmi.org/app/uploads/2017/05/RMI_Document_Repository_Public-Reprts_T96-10_UHVPrinDsn.pdf

Chicago

Moore, Timothy C. Ultralight Hybrid Vehicles: Principles and Design. RMI, 1996. https://rmi.org/app/uploads/2017/05/RMI_Document_Repository_Public-Reprts_T96-10_UHVPrinDsn.pdf.

Wikipedia

{{cite report |last1=Moore |first1=Timothy C. |title=Ultralight Hybrid Vehicles: Principles and Design |publisher=RMI |date=1996 |url=https://rmi.org/app/uploads/2017/05/RMI_Document_Repository_Public-Reprts_T96-10_UHVPrinDsn.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{moore1996ultralight, author = {Moore, Timothy C.}, title = {{Ultralight Hybrid Vehicles: Principles and Design}}, institution = {RMI}, year = {1996}, url = {https://rmi.org/app/uploads/2017/05/RMI_Document_Repository_Public-Reprts_T96-10_UHVPrinDsn.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }