Jim Hill wrote:
>
> All true. You can, as Irv notes, have a roll bar made up (or a "street" roll
> bar strengthened) by a welding shop or a circle track shop, but make SURE
> that they understand precisely what the requirements are. The rules of most
> racing organizations require the use of certain materials, in addition to
> design specifications.
>
> The truth is that a roll bar made for serious SCCA road racing performs a
> number of functions besides simple roll-over protection. There are serious
> chassis-strengthening considerations involved. Under some circumstances, a
> roll cage may be necessary.
It's important to note that there are some shops out there which believe
that the higher tensile strength material used, the better, and for a
roll bar or cage, that thinking is quite wrong. The material used has to
absorb loads, rather resist them. For that reason, the steel chosen
should be either 1010 or 1020 mild seamless tubing, rather than
something like 4130. The thickness and section modulus of the tubing
will determine the resistance to deflection, rather than will the
material. Mild steel will deform, and therefore, absorb more energy
before failing. That's important--Young's Modulus is the same for most
steels--and the higher the tensile strength, the lower the elongation.
That means that the less ductile the material, the more brittle it is,
and the more likely it is to break under load, rather than bend. One
doesn't want shards of broken metal flying around the cockpit as the car
is rolling over. (!)
If one is thinking of having a custom unit made, or buying one from a
specialty shop, be sure to ask about the materials used. Most race specs
are fairly specific about such. If you are in any doubt about what to
use, get the race class rules first, and then go shopping for a roll bar
or cage. That way, you can be sure about the materials required, and the
attachments necessary to meet the rules of whatever class in which you
intend to run, even if occasionally.
Cheers.
--
Michael D. Porter
Roswell, NM
[mailto: mporter@zianet.com]
`70 GT6+ (being refurbished, slowly)
`71 GT6 Mk. III (organ donor)
`72 GT6 Mk. III (daily driver)
`64 TR4 (awaiting intensive care)
`80 TR7 (3.8 liter Buick-powered)
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