Chassis stiffness and weight/cost

Hey Guys,

My datsun replica has a locost-type frame (i.e., mostly one inch square tubing.) The area where a real 1930s street rod would use frame rails has two horizontal tubes, separated by 1-inch high spacers (also made of 1-inch square tubing) I know that I'm going to weld 1/4 inch x 3 inch flat rod along the outside of this area so it looks like a normal frame rail when you look at the car from the outside.

What should I do to the inside of these "frame rails"?
- Should I weld flat rod along the inside surface to provide additional stiffness?
- Should I weld thick 2x3 tubing along the inside for even more stiffness?
* - Should I leave it open on the inside so I don't create little pockets where rust can develop?

Keep in mind that I plan to use this car for many years long after the $2011 challenge. The expected use is 1) car shows, 2) local autocrosses (...where I don't anticipate having any competition in my car class)

[edit - stupid formating....]

More pictures of what you have to work with now... and I like where this is going.

fill the gaps with foam to eliminate rus and cover inside with 1/16th sheetmetal to make it all look perfectly clean.

ronholm wrote: More pictures of what you have to work with now... and I like where this is going.

Yea more pics I am having a hard time visualizing what you are talking about with the one pic and the text. maybe a sketch?

I think 1/4" on anything on that car is overkill. I would use 14 ga (.075ish) Max. on both inner and outer, 16ga would be fine too. I would probably drill 1/4" holes and plug weld it to your vertical portions just for stiffness's sake. Realistically what you are adding is primarily for style as your overabundance of vertical pieces should provide a good amount of stiffness in those members. If you wanted minimum weight and max long term life you would only fill the areas that are open now with sheet similar in gauge to the tubing and grind it all smooth. This will leave you with no radius's on the top of the bottom tube to collect water between it and the vertical sheet.

Good luck, the car looks great. Something similar is on my list of "someday" projects.

Capt Slow wrote: Yea more pics I am having a hard time visualizing what you are talking about with the one pic and the text. maybe a sketch?

Maybe this will be more clear.....This is the portion of the frame I was discussing.

You can also see it closer up in this picture.

nocones wrote: I think 1/4" on anything on that car is overkill. I would use 14 ga (.075ish) Max. on both inner and outer, 16ga would be fine too. I would probably drill 1/4" holes and plug weld it to your vertical portions just for stiffness's sake. Realistically what you are adding is primarily for style as your overabundance of vertical pieces should provide a good amount of stiffness in those members. If you wanted minimum weight and max long term life you would only fill the areas that are open now with sheet similar in gauge to the tubing and grind it all smooth. This will leave you with no radius's on the top of the bottom tube to collect water between it and the vertical sheet. Good luck, the car looks great. Something similar is on my list of "someday" projects.

+1