I have a glass fibre car with a rotten mild steel space frame chassis. Is it feasible to replace (partially replace) with your carbon fibre tubes and sections? I mean would they be strong enough. The main rust is in the main backbone chassis and the sections that come out along the sills. If i have a 1inch mild steel tube section what would i replace that with for same strength?

I would replace complete section for instance the whole backbone not just patch up the rusty bit.

Graham

simpler solution might be to repair the old chasis then get it hot dip galvanised. Then powder coat/paint it then fill all the voids with a good corrosion inhibitor.

If you had the time, money, space and engineering knowledge, you could build a carbon chassis.   However, if you do a bit of research into carbon chassis technology you will find most are either a complete carbon monococque or a central carbon tub with bolt on front/rear subframes.

F1 cars are an obvious example but there are quite a lot of sports/race/supercars knocking about with carbon monococques/centre tubs.

As Matt eludes to, using just a tubular carbon copy of the steel spaceframe would be difficult and leave issues surrounding crash design.  Hence why most carbon cars are a monocoque design which best utilises the strengths of the carbon/composite material.

Also in terms of failure modes, a conventional steel structure it is allowable in the design to have crumple zones and an element of deformation to absorb the energy. With the failure of carbon structures generally being a total failure of the part, it means you need to make the part stronger so that the essential central tub does not fail and hence protects the occupants.