Ok guys I was going to see if someone could help me out here. I have a 1970 triumph T100R with a David Bird hard tail 6" stretch 2.5" drop. I plain on running a 21" wheel front and rear. My question is what size springer would I need to keep the frame nice and level to the ground? My guess is 4 under... Let me know any other info you may need. Thanks for any help anyone could give.