frame building

I know there a way to bend steel, but I need to know what is best way to do it because i ask for my a cruiser bike frame has a two inch tire and 3 inch of clearance but i want to have a 3 inch fat tire to 4 inch fat tire depending how much i can bend the steel. I want at least 1/2 inch...

I maybe trying to reinvent the wheel right now but when it comes to frames do the they have to be welded, I've always wanted a motorized bicycle that had a more of a cruiser look to it and while a beach cruiser comes close I wonder what if you where to drop the bottom bar where the engine mounts...