Yes, as the API standards for motorcycle engine oils progress from SA to SN, there is generally a reduction in the use of viscosity index (VI) improvers/modifiers. The API (American Petroleum Institute) sets these standards to ensure the quality and performance of engine oils.
Viscosity index improvers/modifiers are additives used in oils to enhance their viscosity-temperature relationship. They help maintain consistent oil viscosity across a range of temperatures, ensuring proper lubrication and protection for the engine.
As the API standards advance, the focus is on formulating oils with improved base oil quality and additive packages, reducing the reliance on viscosity index improvers. This is because relying too heavily on VI improvers can have certain drawbacks, such as shear stability issues, increased susceptibility to mechanical breakdown, and decreased oil performance over time.
The newer API standards, such as SM and SN, emphasize the use of higher-quality base oils and more advanced additive technology. These formulations are designed to provide improved protection, better high-temperature stability, and enhanced fuel economy without relying heavily on VI improvers.
Different oil manufacturers may use different approaches and formulations to meet the API standards while achieving their desired performance characteristics. Therefore, it's important to refer to the specific oil's specifications and consult the manufacturer's recommendations for the best oil choice for your motorcycle.