I don't know much about car setup at all, but after my first (and only) online race at Feldbergring, someone sent me their setup for the Porsche 718RS60. When I tried it out, it was like my dream car - it behaved exactly as I could have hoped for. I was able to make it turn sharper by making the back step out, heavy braking into hairpins was vastly improved, it was just a joy to drive.
I looked at what he changed, how this guy managed to turn this lovely but understeery car into a nimble, lively racer, and tried to apply the same changes to the Lotus 25, and it worked!
(I also tried it with the Masterati 250F 6-cyl too).
I have attached the Lotus 25 setup I use for all tracks now, but I mostly drive on twisty turny German roads from the 1950s