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Building a Roll Cage: Design Tips & Tricks

August 30, 2022  -  Chassis, Steering & Suspension

44 People Found This Article Helpful

Building your own roll cage is one of the most important things you will do in your race vehicle to provide protection for you in the event of a crash. There are many things to understand and plan for when researching how to build a roll cage. There is nothing worse than showing up at the track and failing the tech inspection because specific rules were not followed. Below are answers to the most common questions about roll cages:

Two Purposes of Roll Cages

The primary means of a roll bar or cage is to protect the driver, but barring such an incident, those bars will serve a daily purpose of stiffening the entire vehicle up and creating less body roll and twist. Each bar added to a roll cage adds another dimension of structural support and rigidity. For example, the X-brace is not only stronger than the straight rear struts, but also provides added torsional strength to the car. The downside, however, is that the X-bar essentially eliminates your back seat.

The benefit of a roll cage is really two-fold. It's designed to protect you first and foremost, but the everyday bonus to the existence of a roll cage is improved stiffness of the vehicle, and that's a big plus for drag racers planting the tires to the ground.

Adding more bars to a roll bar/cage not only adds to the structural integrity from a safety standpoint, but each additional bar presents more rigidity to the chassis. The more points you put in the car, the stiffer the platform of the car is going to be. The more horsepower and torque the engine has, and the better 'bite' the car gets, and the more it's going to try twisting on the launch. More bars increases how rigid the chassis will be. Maintaining the stiffness within the body and chassis allows shock and suspension tuning adjustments to deliver results you can truly see.

How to Design a Roll Cage

There are many important decisions to make when learning how to build a roll cage for a race car. If you are planning to race in any event, the first thing to research are the rules for the roll cage in your vehicle. This can be accomplished by calling the racetrack and asking a tech official or by researching online for the rulebook and the corresponding class requirements that you will need to follow in order to race. Full-body, open-body, dragsters, and street vehicles all have their own specific regulations to comply with. Examples include the roll bar diameter, minimum and maximum distances from the driver, angles, and more. The number of mounting points also needs to be determined, based on the rules for the class you will be participating (for example, 4-point, 6-point, 8-point, 10-point, and 12-point). How the roll cage is welded is also defined in the rule book. How fast the vehicle is at the racetrack along with its top speed has an impact on the safety requirements as the faster the car is, the more safety and strength needs to be added. Faster cars will require certification by a NHRA official who will add a serialized sticker to your roll cage when it is approved. If you have any additional questions, contact us and a  JEGS tech specialist can also help you.

4 point roll cage
4-point roll cage
6 point roll cage
6-point roll cage
8 point roll cage
8-point roll cage
10 point roll cage
10-point roll cage
12 point roll cage
12-point roll cage

Buying a Cage For The Street Versus The Strip

Something to keep in mind when you're in the market for a roll cage is the fact that what's designed to save your life in a dedicated race car isn't necessarily optimum for a car that spends all or most of its life on the street. Most chassis builders generally build their roll bars/cages to NHRA specifications regardless, but these chassis builders also know there are safety discrepancies between a street and a race car. What's designed to keep you safe on the track can be your worst enemy on the street. Imagine getting broadsided and striking the cage without a helmet on. For this reason, many chassis builders will shy a customer away from a full roll cage if the primary use of the vehicle is street driving. There's no specific rule of thumb for track versus street split time, but if you're doing a considerable amount of street driving, a roll bar might be your best, and safest, bet.

What Size Tubing for Roll Cage?

The correct size tubing for building a roll cage depends on the race class you will be participating in. To find the correct size, either call the racetrack and speak to a tech inspector or research online the rulebook with all of the details on the size of the tubing as well as how it must be welded, and where it needs to be specifically located within your vehicle. The most common tubing diameters are 1-5/8” and 1-3/4”, depending on the requirements. For NHRA, all tubing has to measure 1-3/4-inch outer diameter, with mild steel .118-inch thickness and Chromoly .083-inch. Swing-out sidebars, popular for many cars that will be driven on the street and climbed in and out of, are permitted on cars running 8.50 and slower, with a number of caveats in terms of the clevis, bolts/pins, and more.

Roll Cage Material

Your choice of material for a roll bar/cage comes down to one of two options: mild steel or Chromoly. Each one, when built within the specifications of the NHRA rulebook, offers the same amount of strength and protection. What it really boils down to then is a tradeoff between cost and speed. How fast do you want to go?

As pointed out above in the NHRA regulations, the minimum wall thickness on mild steel is more than that of Chromoly to achieve the same result, and that is because, by nature, Chromoly offers more strength pound-for-pound, so to speak.

All roll bars/cages constructed of 4130 Chromoly tubings must be welded using an approved TIG heliarc process, while mild steel must be done with an approved MIG wire feed or TIG heliarc process. Grinding and plating of the welds is prohibited, so keep these points in mind if you're a do-it-yourselfer.

Roll Cage Material Weight

By nature and pound for pound, Chromoly is a stronger material than mild steel, and that allows for Chromoly to be a thinner wall tubing (.083″ compared to .113″). This gives Chromoly a distinct advantage in terms of weight, but that advantage comes at a cost that customers must weigh (no pun intended) before they build.

Mild steel is far less expensive than Chromoly but comes with the disadvantage of more weight. For the grassroots racer on a budget that we're targeting here, that cost versus weight decision can be a big one.

Using a 12-point roll cage as an example, the mild steel version will tip the scales about 50-60 pounds heavier than the Chromoly, but is nearly double the price.

Where to Buy Roll Cage Tubing

JEGS offers mild steel roll bar tubing in both 1-5/8” and 1-3/4” sizes as well as chrome moly steel tubing. A JEGS tech specialist can also help you find the tubing you need for your application as well as information on how to build roll cage.

Typical drag car chassis with added "Funny Car" roll cage configuration

How to Build a Tube Frame Chassis

When building a tube frame chassis, there are many important decisions to make, similar to building a roll cage. If you are planning to race in any event, the first thing to research are the rules for the chassis in your specific vehicle. Calling the racetrack and asking a tech or researching online for the rulebook and the corresponding class requirements that you will need to follow in order to race is the best option. How fast the vehicle is at the racetrack along with its top speed at the track has an impact on the safety requirements as well as the type of vehicle you are building. The size and thickness of the tubing is also dependent on the vehicle and class. JEGS offers many different roll cage kits to help make the installation process easier. There are also rules on how the chassis is welded that you need to be aware of. Faster cars will require certification by a NHRA official who will add a serialized sticker to your chassis when it is approved. If you have any additional questions, A JEGS tech specialist can also help you. Once you have the rules and details on what the tube chassis requirements are, you can begin locating components and building the tube chassis. JEGS offers many roll cages and tube chassis components to help you complete your next build.

alston racing pro gas tube chassis
tube frame chassis

NHRA Regulations You Should Know

The National Hot Rod Association, the premier governing body in the sport of drag racing, outlines a number of requirements for roll bars and roll cages for racers competing at sanctioned tracks and events the world over, based on elapsed time and, in some cases, on speed.

Vehicles running 11.00 to 11.49 in the 1/4-mile or 7.00 to 7.35 in the 1/8-mile (including those with T-tops), convertibles running 11.00 to 13.49 (7.00 to 8.25), and dune-buggy-type vehicles running 12.00 and slower are required to have a roll bar installed in the vehicle.

Stepping up the performance ladder, a roll cage is mandatory for any vehicle running 10.99 (6.99) or quicker or exceeding 135 mph. In any full-bodied vehicle however that maintains an unaltered firewall, floor, and body running between 10.00 and 10.99 (6.40 and 6.99) a roll bar is permitted in place of a roll cage.

Despite the regulations, nothing says you can't overdo your setup and run a full 12- or 14-point cage on a 12-second car. The fact is, you can never be too safe.

If you're working with a car with an OEM frame, the roll bar/cage must be attached to the frame, while in uni-body cars (which make up most late model cars), a 6-inch square steel plate measuring 1/8-inch thick must be welded to the floor as a base for each bar that makes its point of contact inside the car. Bolted-in bars require a pair of 6-inch steel plates — one underneath and one above, with four 3/8-inch bolts through the rocker sill to hold the two plates together.

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