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by Ken Myers
Whether your goal is to run HPDE or to be the next Mario Andretti,
you need to think about your safety while on track. This article
will explore the ins and outs of roll bars and roll cages.
NASA’s High Performance Driving Events (HPDE) are a very safe
way to learn how to handle your car and drive the line on the race
track. These events are not designed to teach you how to race, there
are other schools that will teach this. All you need to run a HPDE
event is your car (in good condition) and a helmet. In a convertible,
you will also need to have a roll bar. This roll bar must be strong
enough to withstand the forces of compression involved in supporting
the full weight of the car. A factory roll bar such as those found
on a Honda S2000 may fulfill this requirement, but “style bars”
or “show bars” found on some other cars would not work.
(If you have a question about your car, call the NASA office.) Road
racing with NASA requires a full cage (defined as 6 or more mounting
points).
Installing a roll bar or roll cage will bring some benefits and
some liabilities. A roll bar (defined here as a protection hoop
with 4 mounting points) will help protect the occupants in the case
of a roll over accident. Added benefits include chassis stiffening
and a place to mount your seat, harnesses, camera mount and more.
Liabilities include a heavier car, hard, unforgiving metal near
your head and less rear visibility. The benefits of adding a full
cage includes even more chassis stiffening, even more protection
(including side impact protection), road race rule compliance, and
a place to mount your window net and rear view mirror. The liabilities
include an even heavier car and poor egress/ingress of your car.
Roll bars and roll cages are not for everyone. Safety is a personal
decision that only you can make. I tend to err on the side of safety.
If something goes wrong on the track, I want to walk away from it.
On the other hand, I don’t want to tear up the inside of my
nice street car. So, safety has to be a compromise. Either I put
the proper safety equipment in my car, or I don’t push hard
on the race track. If I keep things under control on the track,
I can minimize my safety concerns.
If I want to push hard on the track, I know the car was not designed
to crash at the speeds we can achieve. For a school car that also
runs on the street, a roll bar would be appropriate. Here we can
achieve roll over protection, and all the other benefits mentioned
above. In a sedan with a back seat you can even get the diagonal
cross brace and shoulder harness bar made removable so that you
can access the rear seat when not racing. Never put a passenger
in a car with roll bar/cage bracing in front of them. This type
of bracing has known to cause severe injury and even death to passengers.
If the car will be a full-out race car, the better option is for
a roll cage. Here we will find that the benefits far outweigh the
liabilities. The added chassis stiffening will allow for better
and more predictable suspension. In turn, you will be able to run
more consistently and your lap times will lower. Adding harnesses
and a better seat will increase your safety and lower lap times
even further.
Running faster laps puts you and your car more on the edge of adhesion.
Driving more on the edge will mean that you will sometimes drive
over the edge thus putting yourself more at risk to having an accident.
Now you are going to be glad that you put in all that safety equipment!
The most frequently asked questions regarding roll bars and cages
have to do with the different types of materials used in their fabrication.
Generally, there are three different materials used: ERW, DOM and
Chrome-moly. ERW stands for Electric Resistance Welded and this
is a mild steel that is made from a flat sheet, rolled up into a
tube and welded. DOM stands for Drawn Over Mandrel. This tubing
is actually ERW tubing that has gone through an extra step to even
out the imperfections and make it stronger. Chrome-moly is an alloy
of steel which incorporates both Chromium and Molybdenum in the
process and is stronger still. NASA’s rule book is very clear
about what tubing is required for different weight cars and different
classes. The rule book will tell you what is allowed and narrow
down the choices.
The benefits of ERW tubing is simply that it is less expensive.
The liabilities is that it is not as strong and therefore you may
need to use a larger size tubing than either DOM or Chrome-moly
(or ERW may not be legal at all). Using a larger tubing size means
more weight and more weight mean a slower car. One must always balance
cost with competitiveness. Remember, almost always there will be
someone out there that can outspend you. A good racer knows where
to budget their money and what will achieve the most gain for the
dollar.
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