I found that the shorter springs the better suit for E4RS. I tried some a bit longer ones like Tamiya and HPI, the soft worked ok but the stiff didn't work well when I tried to set 5mm ride height, I even moved up the retainer to max but the min ride height I could get was about 7mm. Well I could use droop setscrew to achieve 5mm, but then I will not have any down travel. That is not a good setup.