CDS vs T45 Rollcages

[tsinc]

I'm sure this has been discussed before but after a quick search online, and on these forums, I couldn't find a resounding answer.

I'm looking at having a weld in cage fitted to my E46 M3 and wanted to ensure it meets MSA/FIA spec for future resale value as well as ensuring it meets minimum safety standards.

The MSA Bluebook states:

Minimum Material

Cold Drawn Seamless Unalloyed Carbon Steel

Minimum Dimensions

Mandatory tubular members
45mm x 2.5mm (1.750″ x 12swg) or 50mmx 2.0mm (2.000” x 14swg).

Optional tubular members
38mm x 2.5mm (1.5” x 0.095”) or 40mm x 2.0mm (1.6” x 0.083”).

So whether you are using CDS, T45 or anything stronger, you HAVE to meet the minimum thickness, correct? So what is the point in spending the extra money on a T45 cage when it will weigh the same as the CDS as they both are required to be of the same minimum thickness? The T45 cage will be stronger but from a weight saving perspective, they will both weigh the same won't they?

Weight could be saved by using thinner walled tubing on the optional members, but a big chunk of the cage is made up of mandatory members which have to meet the minimum thickness.

So how do some cage manufacturers sell a T45 cage, that weighs 20kg less than it's CDS counterpart, is below the minimum thickness stated above in order to save that 20kg, yet it is being sold as MSA/FIA spec and certified?

I was solely looking at a T45 cage to save 20kg but from reading the Bluebook I don't understand how it can be certified yet be below the minimum thickness…

Happy to be educated on the use of T45/CDS and MSA /FIA specs as I know little other than what I have read online recently.

[tsinc]

So a thinner walled T45 cage can still meet MSA/FIA spec even if it is below the minimum diameter/thickness stated in Bluebook?

I've read you can get a bespoke cage certified but a four figure cost seems excessive.

[tsinc]

boy said:

I guess a mass manufactured cage will be cad designed/ FE analysed and then certified by the fia/msa. You can then play tunes with the material dimensions to minimise weight etc quiet easily.

So an exception to the minimum dimensions of the mandatory members is if the design was tested and certified? But to do this on a bespoke design would cost well well in to four figures as the design has to be tested at MIRA and then certified by MSA.

I was going to opt for a bespoke T45 TIG welded cage but if I wanted to use the 38mm or 40mm throughout it wouldn't meet MSA/FIA spec as mentioned in the first post. But only for thickness, not strength. I don't really understand how they can set a minimum thickness regardless of what material is being used, using something with the same strength but 50% of the thickness (for arguments sake) produces the same performance but wouldn't technically meet their requirements due to it being based on thickness and not strength..

The options seem to be either use a certified off the shelf cage, ie Custom Cages, or have a bespoke cage designed, tested at MIRA, certified and then built in to the shell. The latter being much more expensive due to the testing/certification process.

Is it the design that is certified rather than the actual cage itself? Could a bespoke cage be built that matches the design of an off the shelf T45 cage that has a ROPS certificate?

boy said:

Are you confident welding a self assy flat pack cage? do you need to remove the roof to weld around any of the joints?

I wouldn't be welding the cage myself but having a professional do it. The car would be stripped to a bare shell with roof removed.