Carbon roofs: load-bearing cages a necessity?

[MechaniX_034]

Hi there, new user here. Recently I've been looking at having a new roof panel made out of carbon fiber(yup, nicked the idea off of the new M3) However, one of my concerns is if it will sacrifice body rigidity even given that the roof can be mounted using the standard SPR(self-piercing rivets) that are original to the vehicle.

Will a load-bearing rol cage be necessary in order to use a part like this, and will the additional weight of such a cage simply offset the 6+kg saving of the roof itself?(I'm thinking that it will, since a lateral member at least will be needed)

Thanks for that, gents!

[TEAM78]

This is a seriously complex question, it depends on which products specifically you intend to use and the lay up process you go for. If you go autoclave and epoxy resin high skill process along with doing the usual calcs such as matrix calcs to check modulus and strength properties in every direction, then compare to original etc then the panel itself will be as strong/stronger than the original panel. The SPR rivet idea is good, i saw this done a uni with good results when used with carbon fibre however I would also bond the panel in as well and it will then probably improve the torsional stiffness of the chassis so long as you ensure the box sections along the roof are closed sections. should work a treat really if your prepared to put up a couple grand for the job. can you justify that expense? i.e. is 2k somewhere else needed more so than on a 6kg mass saving on the project.

[MechaniX_034]

Thanks so much for that; this question has been plagueing me for the good portion of a month. I agree; 6kg in the roof might be negligable on a Club Sedan(we aren't gunning for hundredths in any way) and yes, the 2 grand is needed in other areas that would yield a greater weight saving in total, as well as a greater overall laptime reduction.

Again, thanks so much!