SAE Engine Oil Divisions

[Jay]

I'm curious as to how the SAE came up with their grade divisions. Why aren't they nice even ranges?

20 weight covers a range of 3.7cSt.
30 weight 3.2cSt
40 weight 3.8cSt
50 weight 5.6cSt
60 weight 4.2cSt

Anybody know how they come up with this?

 

[MolaKule]

JAy,

Partly historical and mostly mathematical, i.e., the way the mathematics yield the resultant numbers.

When starting out to define viscosites, the main goal was not to have even numbers or numbers without decimal points, but to define a range of viscosities that met the International acceptance of the definition of dynamic and kinematic viscosities.

 

[Jay]

Thanks MolaKule.