The secondary research process involved comprehensive analysis of regulatory databases, industry publications, automotive technical standards, and authoritative transportation organizations. Key sources included the National Highway Traffic Safety Administration (NHTSA), US Environmental Protection Agency (EPA), European Commission Transport Database, UNECE World Forum for Harmonization of Vehicle Regulations, Automotive Research Association (ARAI/ICAT India), China Association of Automobile Manufacturers (CAAM), and Society of Indian Automobile Manufacturers (SIAM).
Industry standards and technical sources comprised SAE International, ASTM International (specifically ASTM E855 for spring specifications), American Iron and Steel Institute (AISI), Organisation Internationale des Constructeurs d'Automobiles (OICA), SMMT (UK), Verband der Automobilindustrie (VDA Germany), Japan Automobile Manufacturers Association (JAMA), and European Automobile Manufacturers' Association (ACEA).
Government and trade statistics were extracted from the US Bureau of Transportation Statistics (BTS), Transport Canada, EU Eurostat Transport Database, National Bureau of Statistics of China, Ministry of Road Transport and Highways (India), and Brazilian Association of Automotive Engineering (AEA).
Commercial and proprietary automotive databases included S&P Global Mobility (formerly IHS Markit), MarkLines Automotive Industry Portal, JATO Dynamics, AutoForecast Solutions, Wards Intelligence, and International Organization of Motor Vehicle Manufacturers statistical yearbooks. These sources were employed to compile data on vehicle production statistics, suspension system specifications, raw material pricing, regulatory compliance standards, and aftermarket volume analysis for parabolic, elliptic, and semi-elliptic leaf spring technologies in the metal and composite material categories.