chassis strengthening question

[Dave Price]

Currently being off work following an Op, my brain is doing a lot of thinking.  I am looking to stiffen and strengthen my Phaeton chassis.  My knowledge of steel structure is in terms of construction,  a building has substantial steel frame that is then braced with very small section steel, such as steel rods or stainless steel cables.  My question is why when strengthening a kit car chassis people fit an additional steel member which is similar in section to the adjacent existing members, could bracing, triangulation, strengthening not be achieved by adding diagonal rods like in a building's structural frame? Thoughts and comments please

[Dave Adams]

Look at my S1 rebuild post. i strengthened my chassis using  1/2" square tube and 1" square tube. the difference in handling was staggering and the improvement huge!

I could tell the difference on my car with in 100yds of driving after the rebuild.

[James Doulton]

I think that rods are good in tension but pretty useless in compression because they buckle, whereas a tube of the same weight will be much stronger in compression before it eventually crumples. In a building then most of the forces act in one direction and are mostly steady but in a car there are regular reversals, side loads and impacts. In terms of ultimate tensile strength then rods or cables might be slightly stronger than tube in tension because of being easier to heat treat, maybe, but tubes make a more rugged construction.

[Paul Sheridan]

Or look at my rebuild here :-     http://www.godspeed.me/forums/viewtopic.php?f=3&t=1055

Similar to what Dave did, but I used the same size box section relative to where I strengthened.