Nick 241,
Your best bet is to obtain the 2004 Blue Book which gives you the full specifications and drawings applicable to all types of vehicles in racing.
The most important thing is that cold drawn SEAMLESS carbon steel with a minimum yield strength of 350 N/mm2 is used and that its minimum dimensions are 48.3dia x 2.6mm for sports racing cars. If it is circuit racing you are thinking of i can give you more definitive guidance on regulations if you care to contact me direct.
Regards,
Graham @ GTA Racing.
