what kind/size/thickness of tubing is best for a mini bike frame?

the bottom bike has a lawn mower engine from the 80s. its a victa 160cc 2stroke engine, its from australia. this engine was modified to run a tillotson carb. i didnt mod it though i got it from school this engine was on a gokart. it was pretty good but at the time i didnt know anything about carbs or performance so it never ran at its best. if it was tuned properly and had a tuned pipe it would have been really fast. if you want a similar engine lawn boy still makes 2 stroke lawn mowers, its very similar to that.

also some of my first few minibikes were 3d and out of square tubing. but i found that its very hard to make the frame straight with so many pieces. personally i cant have a crooked frame so i started to make flat frames because i can just lay it out on a table and it will be straight.
Well i bought the tubing today. I went with 1/8 inch thick 1 inch square tubing. I will just cut the angles and weld the pieces together rather than bending anything. I also have purchased a magnetic angle finder to keep everything symmetrical. I will start a thread in the project section for my progress from here on in.

One more question though. What is the average length of a larger sized mini bike frame from front to back?

I measure an existing mini bike berore I build a frame. Then draw it full scale on cardboard and alter as I please. You will have to decide on rake angle and other things like frame width and etc. Draw in the wheels and engine. If you don't you could end up with a gas tank hitting a tire or some such problem. In your first post you mentioned that you are going to use a swing arm at the rear. That will, for sure, require a jackshaft be used. Locate all that stuff in the drawing and you will make a lot fewer mistakes and re-dos. Honest.
i would also like to add to the above that you should have your back wheel before you do anything. have your brakes and sproket all put together with the back wheel and have the tire on. with this you will be able to know how wide the rear end should be and where the brakes will go. as mentioned above you should also have an idea of how it will be made, draw a little drawing of everything or at least know how everything will go together. also plan out the rear suspension if you are going to have any. figure out the travel and make sure that the chain pivots between the swing arm pivot point symmetrically. in short the geometry should be good. also plan out the trail otherwise it wont steer well.
I wonder if he got it done yet lol
I wish he had and then sold a few, the Grattan Hound Dog is in the top 3 on my minibike bucket list as is the Hot Dog. Seen you on FB Bryan, the Predator page. If a dude named Andy sends you a friend request it will be me, one of your many fans here and on Youtube. Perhaps you could build one, I can see you pie cutting the square tubing and making it look like you bent it as I type here. Should I ever attempt it that will be my method although is will look like hell because my hands shake worse now and it's progressing, I need a cure or a to hire a welder one or the other.