im building a frame like you would see on maybe a exotic or a baja truck or dune buggy. what diameter should i use

 

Each of the types of cars you mentioned has different requirements. What size of tubing you use depends on how much the car will weigh, what type of loads go into it (the pounding of a baja truck or the smaller loads of an exotic car,) and most importantly is how well you engineer it. If a frame is poorly designed, the tubes will be overloaded and the welds will fail. If a frame is well engineered, it will be indestructible.

You need to read "Chassis Engineering" by Herb Adams. Lots of pictures that show what works and why, and lots of good advice.

I have built roll cages, car hauling trailers, and many other structural things. Designing a car chassis is not an easy thing. It is like the foundation of a house: if you screw up your foundation, then everything you build on top of it will be bad too.

 

http://www.amazon.com/exec/obidos/tg...books&n=507846

$10.60

 

thanks for the reference

 

Second Herb Adams' book, lots of good info. I'll point out one fact: large diameter tubing with a thin wall is stiffer than small diameter thick wall. For instance, 1 1/2" .095 wall tubing is stiffer than 1" .095 wall. To get a comparable stiffness, you'd have to use thickwall (say, 1 1/8 .120 wall) small diameter tubing, which is more expensive and heavier.

Also: Buy a tubing notcher, it saves a LOT of time and aggravation. I just got through building rear lower control arms for my rotary Spitfire (I used 1 1/16 .105 wall tubing for that, BTW) and the notcher saved a bunch of time and aggravation. The other advice: measure THREE times, and cut once.