RE: Tamiya KT - A beginners build
Proof will be in the pudding when you put metal tracks on. Spring has to be pretty stiff for them, and the idler support drum has to move freely in it's axis of movement to work well. I use straight 10W-40 oil to lube the one Tiger I have spring loaded idlers in. Works, but of course with the talc fine powdered dust we have here in summer, needs cleaning after long runs.