Honestly, almost any hobby with depth has one, but I know of no good generalist sites. Here is a good example; Bobtheoilguy - Forum dedicated to automotive lu

Honestly, almost any hobby with depth has one, but I know of no good generalist sites. Here is a good example; Bobtheoilguy - Forum dedicated to automotive lubricants. Some very in depth analysis and company insiders on occasion. Many users regularly send in oil for testing and post results. Great for info on the changing formulations of oil standards, and common additive packages. Very useful for me, owning old and new cars and bikes.