While there are many manufacturers and
suppliers of roll bars, some of the bars offered
on the market are of poor quality and
construction and could be more of a danger than
an asset in an accident. Here are a few points
to observe when choosing a roll bar to assure
you obtain the best quality available
First, the tubing should have a minimum
outside diameter of 1.5" x .120" thickness in
seamless mild steel for a Spridget or 1.75" x
.120" for a MGB. The mild steel should have the
specification CDS or DOM. If you want to go
absolutely first class, then a chrome molly
alloy steel, SAE 4125, or SAE 4130. For the
maximum protection, T45 should be used. For home
constructed roll bars, mild steel is recommended
due to the welding problems involved in
fabricating chrome molly.
The hoop should be built from on continuous
length of tubing and show no evidence of
crimping at the bends, and have two braces of
equal length attached as close as possible to
the top of the hoop. Certainly, no more than 6"
below the top, and with an inclined angle of 30
degrees. The braces can be made of slightly
smaller diameter than the main hoop, but
certainly no smaller than 3 quarters of the
diameter. A good quality bar usually has the
braces the same diameter.
While most people choose street bars which
will enable them to retain use of the
convertible top, it should be kept in mind that
for maximum protection, the bar should extend
above the driver's head by at least 2". Usually,
roll bars have mounting plates welded to the
bottom of them. The mounting plates should be a
minimum of 3/16" thickness and 4" x 4" with
equal size back-up plates and be attached at
each point with four bolts at least 3/8" in
diameter and with a minimum grade of SAE 5.
Welding should be of the heli-arc type showing a
nice, clean continuous bead without any burn
holes or cavities. Also, be sure when purchasing
the roll bar, that the manufacturer states
clearly that the seat travel and top operation
are not effected if that is of importance.
Usually if a roll bar is purchased through
one of the larger supply houses, the
specifications can be obtained ahead of time and
you will not be disappointed.
Finally, one word of warning. Stay away from
low priced chromium plated roll hoops which are
made of thin tubing and in the event of a
serious accident or roll over, could result in
the roll bar wrapping itself around your neck!
Your life is not worth saving a few bucks!
If you are using you Spridget for slalom and
gymkhana type events, the organizers may require
additional specifications and if you are
contemplating constructing your own roll bar,
then an excellent source of information is
contained in the SCCA General Competition Rules;
Appendix "Z", from which some of the foregoing
information was extracted.
UPDATE:
The UK Motor Sports Association, the FIA
associate for the UK, stipulates minimum
safe dimensions for a simple roll cage as:
one hoop, braced to the rear wheel arches, the
minimum is 48.3mm (1.9") diameter x 2.6mm (.1")
thickness.
(MSA regulation Q:1.5.2)
Remember, this page is meant to general
information only. Always double check with
Sanctioning Bodies for the latest safety
requirements. Remember, your safety should
always be of paramount concern; never a place to
save a few bucks!