"Old school" motorcycle front suspension regularly used "fork oil" with advertised weights of 20 - 30. When the more sophisticated cartridge-style forks using tunable stacked shims came into play, those units were typically spec'd to use 5 - 7.5 suspension fluid. One of the reasons was because the heavier weight lubes broke down so much faster when exposed to on-track demands. I just found this list of various manufacturers' suspension fluid specs to use for reference. Maybe it'll help. https://transmoto.com.au/comparative-oil-weights-table/