Nope no tricks, just gotta have the right die for the tube. I assume you are doing mild steel, wall thickness is a big deal. If you get too thin it'll crink on you as well.
What you probably have is a pipe bender, they measure stuff different than tubing. Are you doing full cage? or a hoop? If full cage then 1 5/8 is right, if you are doing a hoop then you'll need 1 3/4". I find it is less expensive to get the auto-weld kit and bend only a few tubes for special concerns, you go bending the whole mess it'll take a whole lot more material than you think. Look them up on the internet, they may sell you just a few critical pieces and then you can do the rest yourself. Thier kits are very good and precise. They are in Pennsylavania, it is either autofab or autoweld - i get them confused. One is a race shop in MD and the other is the bender folks with the kits.