Back to this topic again. My 5x5 tube ended up having a 3/16" wall and weighs a ton. My biggest concern is torsional ridgidity. Ladder frames are the worst type but that's what I've got to work with. I thought of going with two 2 1/2 " dia tubes space frame style but they end up being the same weight as a single piece of 6x3 tube. I'm running a '97 T-bird rear IRS and an '06 crown vic front susp. I'm thinking of running the 6x3x.125 tube as the main rails with 3x3x.125 tube extensions front & back. I want to put an X through the center too. The large tube should greatly increase stiffness but because of its size I can go with the thinner wall. I don't want my Studebaker truck to weigh more than 3500 lbs. Stock was 2900. It will run a beefed 300"-6 so no super power. I see a lot of frames made from 2x4 beer can but I can't imagine them being too stable. I calculate that the frame should weigh around 450 lbs. How does that compare to what's normal? By the way, 5x5x.187" would add another 80 lbs.