Wondering ‘how to build a roll cage?’ Well, roll cage designing isn’t as complicated as you might have imagined. Still, you shouldn’t take it too lightly.
Roll cages are a necessity for a variety of race cars and off-road vehicles. The reason why is the aggressive driving style involved. They are an integral part on which the driver depends. Therefore, you cannot take any chances with its structural design, can you?
Fortunately, you do not need a professional to construct a race car roll cage for you. You can even purchase DIY roll cage kits from manufacturers complete with all the information, components needed, and assembly instructions. What you need is expert advice and guidance, which you will find here in abundance.
In this article, you are going to learn all there is to know about race car roll cage designs for race cars and other vehicles. You can learn how to build a race car roll cage, along with some expert advice that only a pro can provide.
So, read this article till the end to learn everything about the basics. You will also get to know about the mistakes to avoid when making a roll cage.
We are going to cover the following topics:
- Part 1: What is a Roll Cage?
- Part 2: Types of Roll Cages
- Part 3: What Makes a Good Roll Cage?
- Part 4: Which Type of Steel is Used for Roll Cages?
- Part 5: What Fabrication Tools Do You Need to Make a Roll Cage?
- Part 6: What is the Cost of Building a Roll Cage?
- Part 7: Steps to Build a Roll Cage
- Part 8: Roll Cage Basics: Things to Keep in Mind
What is a Roll Cage?
In layman terms, a roll cage is a protective cage or frame designed to keep the driver of a vehicle safe. For instance, in the event of a crash (which is pretty common in off-roading, high-performance drag racing, and car racing), the roll cage prevents the vehicle from crumbling, saving the driver.
While they are usually applied to race cars, tractors, and off-road vehicles, many streetcars today also use them.
Some people confuse a roll cage with a roll bar, but there is a difference between the two. For one thing, a roll bar is a single bar or hoop behind the driver that protects the driver’s head and shoulders.
On the other hand, a roll cage is a construction of multiple metal tubes that offers the driver significantly greater protection than a roll bar.
Types of Roll Cages
There are many different models since specific applications call for a specific design.
An important thing to understand is that you cannot randomly join together metal tubes to make a frame and call it a roll cage. How well a roll cage protects the driver is greatly dependent on the design.
For this reason, there are many different designs available, applicable for various uses. We will cover some design basics in Part 7.
Even the classification of these structures can be done in multiple ways:
2.1 Roll Cage Classification Based on Installation
Based on how they are installed, there are two types:
Bolt-in kits are installed in vehicles with the help of bolts. It means that the bolts and structure can be removed and reinstalled with ease. Another advantage is that these come powder coated, so no added paint layers are required.
However, they do not protect as well as welded versions. They are generally used on rally cars or in non-racing applications.
These require a professional welder to weld the roll cage into a car. This makes the roll cage considerably stronger to withstand collisions, as compared to bolt-in versions. All major sporting events require this type.
2.2 Classification based on X-Point System
When you try buying a roll cage in the market or learn fabrication techniques to build a roll cage, you will often come across terms like 4 point roll cages, 5 point roll cages, 8 point roll cages, and so on. So what exactly do these terms mean?
In simple terms, a roll cage that has ‘X points’ is a roll cage attached to the car body at X number of points. Different sporting events require different point versions for cars to be eligible to participate.
While the basic 4-point cage provides only overhead protection, variants with more components such as an 8 point roll cage also protect the driver from other sides. Additionally, diagonal sidebars in high-end roll variants prevent the roll cage from collapsing under the vehicle’s weight.
Below are 3 examples of various roll cage designs based on the x-point system:
What Makes a Good Roll Cage?
When it comes to making a good roll cage, you need to focus on multiple factors and ensure your cage satisfies all the criteria. Some of the factors that contribute toward making a perfect roll cage are:
- Legality and Eligibility – First things first, the roll cage that you are building should satisfy the legal requirements of your country or state. After that, make sure that the particular cage material and design are eligible for the purpose. For instance, different racing events have different eligibility criteria.
- Material – A roll cage is all about structural integrity. Therefore, the craftsmanship, fabrication techniques, and materials will decide if it is a good roll cage or not. We will talk about the best material for a roll cage in later sections.
- Contact Points – Many people make the mistake of welding the roll cage to the vehicle floor since it is the easiest thing to do. However, in the event of an accident or overturn, the vehicle floor can tear easily from the weight of the roll cage. Therefore, the best fabrication technique is to weld the roll cage to the boxed sills.
- Weld Quality – For maximum safety, and to make sure that the roll cage will hold together in the event of an accident and prevent injury to the driver, you need to weld it properly. For this purpose, Tungsten Inert Gas (TIG) Welding is the best way to go. However, Metal Inert Gas (MIG) Welding is also popular for welding.
- Minimum Gap With Car Body – In a good roll cage, the gap between the cage bars and the car body should be as little as possible. The greater this space, the less internal space is present in the vehicle. This gap also reduces the safety protection provided by the roll cage. So make the necessary adjustments to keep this gap down to a minimum.
- Don’t Forget to Paint – How will painting a roll cage make it stronger? Well, it won’t. However, painting the roll cage is going to make your vehicle a lot more aesthetically pleasing than using an unpainted roll cage with the ugly color of metal and weld splatter visible.
Which Type of Steel is Used for Roll Cages?
There are a lot of options for the type of mild steel or other you can use to build a roll cage. Many people often compare Cold Drawn Seamless (CDS) or Drawn Over Mandrel (DOM) to other grades of mild steel. However, it is not the correct thing to do as CDS/DOM are methods of manufacturing rather than a type of mild steel. The most commonly used high-strength mild steel tubing material used is made by the CDS and DOM methods, so you will see that used to describe many roll cage materials. Please remember that is NOT an alloy/metal, it is a process sued to make tubing.
We wrote this article for users in the USA and abroad, so please consider the specified locations (in parenthesis) if we are restricting the availability or common use of any material to certain regions. You should always use what your racing regulations or safety inspector require, but some of the best steels that you can use to make a roll cage are:
1020 Mild Steel (Common in the United States)
1020 DOM is a medium strength alloy designated by the American Iron and Steel Institute. The number is a series (1000), and a percent of carbon by weight (20 in this case, which is .2% by weight). This is a general purpose steel that was not designed specifically for motorsports use. It is highly weldable, has great bending properties, and is also easy to machine. It is used for a broad range of structural applications from suspension parts to bridges to hydraulic cylinders.
This steel offers a minimum tensile strength of 85,000 PSI (586 N/mm2), a minimum yield stress of (77,000 PSI (530 N/mm2). We gathered this data from the Machinery’s Handbook, 28th Edition.
ROPT510 Mild Steel (Common in Europe/Asia)
Roll Over Protection Tube 510 has a special high-quality rating specially designed for its safety application in roll cages and car chassis. This material meets the official specifications of most authorities, so it is a good choice when it comes to building cages for drag racing and speed racing events.
ROPT510 is strong as well as highly formable. This means that it is easy to bend this material while making a roll cage without worrying about cracks or breaks. It also leads to high impact absorption during collisions.
It offers a minimum tensile strength of 510 N/mm2, a minimum 0.2% yield stress of 370 N/mm2, and a minimum elongation of 25%.
BS4 T45 to BS5 T100 Steel (Common for FIA and in Europe)
BS4 T45 to BS5 T100 is commonly called T45 steel. It has been popular for a long time, being used in multiple applications, especially for FIA and stage rally racing. It is stronger than mild steel tubing and is even used in the aerospace industry.
T45 is ideal for cars for racing events. It is carbon-manganese steel of very high tensile strength. That means that a thinner wall thickness of this variant can make a sufficiently strong roll cage (when allowed by regulations for your racing application). It is much stronger than regular mild steel.
It offers a minimum tensile strength of 700-900 N/mm2, minimum 0.2% yield stress of 620 N/mm2, and a minimum elongation of 15%.
15CDV6 1.7734 (most common in Europe)
15CDV6 is a steel of chromium, molybdenum, and vanadium alloys. This steel is famous for its high degree of toughness, bendability, and ease of welding. It is interesting to note that 15CDV6 is one of the most expensive roll cage materials. But it is also much stronger than simple mild steel.
Some of its properties include a minimum tensile strength of 980-1180 N/mm2, minimum 0.2% yield stress of 790 N/mm2 and a minimum elongation of 10%. You will have to see if your tech inspector will allow you to use this material in your cage (of course).
4130 Chromoly (common world wide)
You might know 4130 by its more popular name- Chromoly Steel. As the name suggests, 4130 is steel created with alloys of chromium and molybdenum. Some of the other representations of 4130 are Chrome-moly, CrMo, CRMO, and CR-MOLY.
4130 has a high strength per unit weight than most other carbon-based steels. However, it presents some challenges in the welding process compared to the other steel types you just read about. The biggest drawback to 4130 is that it becomes brittle in the HAZ (heat affected zone) where you weld. This makes 4130 most likely to break right next to welded joints if it is ever under enough stress to fracture. Heat treating the cage after final welding is the only way to reduce this risk (when done correctly).
Some racing organizations, such as the SFI, require very tight gaps in fit-up prior to welding when chromoly is used. Since the SFI allows thinner walled tubing when 4130 is used, the fabrication must be top notch. This is why they require TIG welding and close fitting notches at all junctions. When we last checked, the SFI/NHRA defined the permissible weld gap as “no more than the thickness of the TIG filler rod used to weld the joint”. That means that if you are using a filler rod that is 3/32″ (about 2.4mm), you can’t have a gap anywhere in the notch larger than that measurement. This care in fabrication will take extra time, but also yield a stronger finished product than a cage made with larger gaps.
This steel is also commonly used in bicycle frames.
Its properties include a minimum tensile strength of 470 N/mm2, minimum 0.2% yield stress of 435 N/mm2, and elongation of 25.5%.
Docol R8 Steel (common world wide)
Docol R8 was designed and produced specifically for motorsports safety applications. Similar to 4130, it is a steel alloy made with chromium and Molybdenum. This material was developed for three key features – high yield strength, ease of bending, and ease of welding. The result is a material that is 10-15% stronger than 4130 chromoly, just as easy to bend, and with a smaller heat affected zone when welded. It is better in every way when compared to 4130. Most racing regulatory bodies (including the NHRA and SFI in the United States) allow it to be used anywhere where they allow 4130 to be used. Verify any material allowance prior to building your cage (of course).
Docol R8 is “weldable” enough that some racing organizations will allow you to MIG weld the entire cage (instead of TIG welding it). This makes Docol allowed as a substitute for 4130, but with the welding process of the thicker mild steel cages in some motorsports. Check with your tech inspector… But if they allow this, you get the ease-of-welding like a 1020 DOM steel cage with the light weight thin-wall-tube of a 4130 cage! The best of both worlds!
Common tensile strengths of Docol R8 are 116,000 PSI (800 N/mm2). The yield strength tested on Docol R8 are 100,000 PSI (689 N/mm2). This data was furnished to us by the manufacturer of Docol, A.E.D.
What is the best material for a roll cage?
As you can see, there are a lot of variations in the properties of different steel types. If you want a material of higher tensile strength, the price will be higher. However, for racing events where the budget is not a concern, top-grade materials like 15CDV6 and Docol R8 (or 4130) are used. Our #1 recommendation is to call your tech inspector or regulatory comitee for the racing you will be doing, and ask them for their top choice. For example, we called the lead tech inspector for safety at the 24 Hours of Lemons in 2023, and he told us that his #1 choice is Docol R8, and not by a small margin!
What is the worst material for a roll cage?
There are many other materials that some fabricators may consider for roll cages. Aluminum has been brought up many times. It has a low yield strength (6061 yield is around 40,000 PSI) and is very brittle, making it a terrible choice for a roll cage. Stainless steel is also discussed for roll cages. While not allowed by any racing organization we know of, it is not the worst choice. It is challenging to weld (TIG and back-purging with shielding gas is a must). The main drawback is it’s low yield strength (35,000 PSI per the Machinery’s Handbook, which is less than half of 1020 steel). This low yield strength means that you would need to build a roll cage from substantially larger diameter and thicker material to have the same strength as a cage made from proper material. There are many grades of stainless, some with higher yield strengths. They get very expensive and usually have other drawbacks. Another material that would be tough to use for a roll cage would be magnesium or one of it’s alloys (uncommon to find in tubing, tough to weld, can be flammable, and is very brittle with a low yield strength). Titanium looks appealing for a roll cage due to it’s excellent yield strength and low weight. It is tremendously expensive, usually brittle, and notoriously challenging to weld. For these obvious reasons, no racing organization that we know of will certify a cage made from titanium, and we don’t blame them. After considering all these materials, we think magnesium wins the trophy for being the absolute worst material to make a roll cage from. You would likely break the cage and have a massive chemical/metal fire risk if you ever tried!
Should you care about weight?
In theory, the weight of a roll cage can be a factor for racing events since heavy ones can impact the speed negatively. An extra thick frame can adversely affect performance. However, most authorities have minimum diameter and wall thickness specifications set for such safety structures.
When you need to meet these specifications, all of the popular materials above will weigh essentially the same. They are all steel alloys. Their densities are all within a negligible percentage. Therefore, your focus should be on choosing a higher grade material than choosing a lighter material.
If you wonder which is the lightest roll cage material you can use without compromising on integrity, it would be the T45, but by a very small margin.
What pipe size should I use for a roll cage?
Do not use pipe! Use Tube! We explain the difference in the tech section here on our web page. Commonly, 1.5” x 0.12” thickness or 1.75” x 0.12” thickness DOM tubes are used. DOM tubes provide the benefit of an extremely tight ID and OD tolerance. We discuss the metal types in great detail earlier in this very article.
On the topic of pipe… There are many off road recreational vehicles built in garages using ASTM A513 grade B pipe. This (in the USA) is a structural pipe, and it is reasonably strong. It is still weaker than every tube we discuss using here in this article and not safe for racing anywhere. We can’t stop people from doing this, but it is safer (and usually far lighter) to build cages and vehicles using the right material.
How much tubing do you need for a roll cage?
The length of tubing for a roll cage depends on its design. For a basic 4×4 roll cage, it is recommended to have 4-6 tubes of 20 feet each. Remember that some material is always wasted in the building process, so it is good to have one spare tube.
What Fabrication Tools Do You Need to Make a Roll Cage?
To make your perfect roll cage, you will require the following fabrication tools:
- Tubing notcher or pipe notcher: Cuts round notches at the end of tubes
- Tubing benders or pipe benders: For corner tube bending fand curves
- Tape Measure
- Carpenter Angle finder
- Metal pipe cutter: For cutting tube into smaller segments
- Hand grinder: Used to make fishmouths and add finishing touches
- Permanent marker
- Level (many smartphones have this feature)
- Welder: Both MIG and TIG welding can create a roll cage
- Protractor or Carpenter Square
If you are a regular DIY enthusiast, you will have many of these fabrication tools already. The rest can be obtained online or through any local hardware store.
What is the Cost of Building a Roll Cage?
Since there are many types of material options available for construction and many different roll cage designs, there is no fixed price for building a roll cage.
Interestingly, the materials for the roll cage are a minor part of the cost. The central part of the cost comes from the tools you require for the job.
For instance, a tube or pipe bender can set you back somewhere between $400-$4200, depending on the thickness of tube you need to bend. The welder will cost you somewhere around $1000.
At the same time, the total cost of materials for a 4 point roll cage with 5-6 bars of steel, footplates, and minor expenses would be about $700.
Other tools like carpentry tools, the tubing notcher, and the grinder are cheaper and will cost you about $100-$200 per tool.
If you use the basic tools instead of their high-end counterparts, the price of a simple roll cage will be about $2000-$2200. This is still considerably cheaper than opting for a store-made roll cage, with the added benefit that the tools you buy can be used multiple times.
Steps to Build the Roll Cage
Various governing bodies authorize and legalize the formal specifications of a roll cage. Before you build a roll cage, you must check the regulatory laws of the rules that will apply to you.
These rules are generally event-specific and are created to protect the life of the driver. For example, a roll cage built for a streetcar will not offer the required security on a track race.
Therefore, make sure that you have gone through the roll cage specifications and they pass the rules and regulations of LEMONS Tech Inspection, FIA, SCCI, NHRA, NASA, Champ Car, or any sanctioning body overseeing the event in which you participate.
The steps listed here will provide general guidance based on the standard specifications, without taking any particular authority rules in mind.
Step 1: Measuring
The process of measuring can be divided into various subparts. Make sure you note down each measurement instead of trying to remember it.
Main Hoop Measurement
Us your tape measure to take the following measurements:
- Height of the car: Height of the roof from the floor. This will be the height of the roll cage.
- Width of the roof: Measure the width of the roof for the roof bar. Also, use an angle finder to measure the angles between the roof and the side of the car. These angles will be used to bend the tubing.
- Car Width: Measure the car width from side to side. Keep in mind that you need to account for any obstructions as well.
- Roof To Side: Determine where you want the roof bar to finish and the sidebar to start. This distance will measure the length of the tube bend.
Door Brace and Rear Brace Measurements
- The horizontal distance between point X (where the braces will join the base plates) and point Y (the hoop).
- The vertical distance between point Z (where the brace will join the hoop) and Point Y.
Once you have these two measurements, you can find out the length of the diagonal brace (XZ) by using the Pythagoras theorem:
XZ2 = XY2 + YZ2
- The horizontal distance between the side tubing and the main hoop. The seat crossmember is positioned between the bars.
- The inside of the main hoop: horizontal distance between the side tubes of the main hoop.
Base plates will join the roll cage with the car floor, acting as the anchor point, or foundation of the structure. Generally, base plates of 3 mm thickness are recommended for most requirements. For a sturdier assembly, thick base plates can provide more stability to the roll cage.
Each base plate is installed at a different point. For example, a base plate is placed near the firewall for door braces and another base plate behind the front car seats for rear braces.
Once you have all the necessary measurements, you can consider the design aspects, as we explain next.
Step 2: Design
Design is a multi-step process in itself, which includes:
Evaluate the cage structure carefully. Every frame is designed to provide maximum protection. Avoid tinkering with any element of the structure to make the cage ‘look cooler’.
Minimum Tube Bending
Remember that a bent tube is weaker than a straight unbent tube, so use bend tubing only where necessary.
In a basic cage design with fewer or no diagonal bracing elements, make sure that you use a gusset where necessary to reduce the stress on the corners.
Triangles are an essential concept of roll cage design. Squares by themselves are structurally weak. So diagonal bar is used in squares to split it into two triangles to provide lateral support to the roll cage. The best practice is to make sure that every tube can be a part of a triangle.
T-junctions are places where a tube joins perpendicularly with another tube. T-junctions are very weak since they can break or bend during an accident. Therefore, avoid T-junctions as much as you can.
It is not a good idea for the down bars to have an excessive lean angle. Additionally, a tube can be added between down bars to provide extra rigidity to the structure. For even greater integrity, an A-pillar can be added between the down bars.
Kicker bars provide added rigidity to the roll cage. They run from the top of the rear hoop towards the down rear of the car.
Roll cage padding is done with high-density foam to provide softer impacts. This padding can add to the aesthetic appeal of the cage.
Step 3: Bending Tubes for the Roll Cage
The process of bending the tube mostly depends on the particular tube bender and die you are using. Even so, there are some general guidelines you should always keep in mind.
An important thing to remember is that you should always use lubricant while bending. Bend All 002 is a good choice, or you can go with coconut oil for a homemade solution. The lubricant will increase the life of your tools and make sure that your bends are clean, with minimum scrap metal.
Most authorities inspect tube bends. You should make sure that any bend is smooth and without deformities in shape. Also, a bend with a deformity is a clear rejection when it comes to safety products.
Also, when you go through the rulebook, check if any particular bends are required. For instance, SCORE and some other regulations insist on Mandrel bends.
Check our video on how to measure and bend 4 point roll cage tubes for more information:
Step 4: Cutting / Notching the tubes
Use a tube notcher to make sure that there are no weaknesses in the weld joint. A tube notcher is essential for precise notching which will make sure that the tubes fit together tightly.
In fact, some rules and regulations are strict about the notch/weld/fitment gap. As an example, the SFI has specified that the maximum notch/weld/fitment gaps between all welding joints can be just as much as the diameter of the welding filler rod material used on TIG welded joints (applies to 4130 and Docol R8 steel structures only).
Step 5: Welding
For high-quality joints, TIG welds are the way to go. Institutions such as the NHRA have even made it compulsory for roll cage construction. Additionally, certain steels like Chromoly tubing are only suitable for TIG welds.
Mild steel can be TIG welded as well as MIG welded. But even with mild steel, MIG welding provides the advantage of costing less than TIG welding.
Before you start welding, make sure that the tubes fit well with each other. Making fishmouths on the tube ends will make this job easy.
Ensure that the welds are fully penetrated; just welding over the surface will not provide a strong joint. Never make the mistake of cleaning welded joints with a grinder, as this will weaken the integrity of the welds.
Roll Cage Basics: Things to Keep in Mind
Now that you have been through the whole guide, here are a few takeaways that you should remember when building a roll cage for your car:
Safety over Aesthetics
When designing a roll cage, many people try to take the ‘cooler’ approach instead of the ‘safer’ approach, as we mentioned in the cage structure section. This is never a wise choice since aesthetics can compromise some aspects of safety gear and security.
Specific over Generic
The majority of vehicles that require accident or rollover safety measures are off-road vehicles or racing cars. These vehicles are designed for an aggressive driving style and a higher risk of accidents. Since these are generally required for high-risk competitions or events, it is important to follow the specific dimensions and specifications of the event instead of generic guidelines.
Costlier is not always better
Of course, costlier materials can be sturdier and costlier tools can have more features. However, you don’t always need these added features for low-level requirements. At times, even a cheaper material can offer more than sufficient protection.
You only have to make it once, and your life depends on it. Therefore, make sure you do everything that your roll cage requires. If gussets are needed, use gussets. If a windshield brace or cross bar is needed, add it. If subframe struts, side bars, seat crossmembers, or door bars are needed, use them. Don’t skimp on the little things as the little things are going to save you.
Weld only if you know-how
Welding is the thing that will hold the cage together. In fact, most structural failures happen due to poor welds. Therefore, take over the welding only if you are confident about it. Otherwise, get the welding done by a professional MIG or TIG welder.
It is a good idea to order more of something now than have to order something over and over when you run out of fit. If you want the whole process to go smoothly, keep spares for the metal tubes, base plates, and the little consumable parts.
A properly constructed roll cage can be the thing that stands between life and death. If you read this article carefully, you will have learned by now everything you need to make a roll cage and how you can build one yourself.
An important takeaway that I would like to reiterate is that the exact specifics of a roll cage are different for different governing organizations. Therefore, check the rulebook of the sanctioning body that applies to you before starting the DIY project.
Frequently Asked Questions
Are half and full roll cages illegal for public roads?
The legality depends on the local laws where the vehicle is being driven. For instance, some cars now come with either half or full rollover protection pre-fitted because it is legal in the region. At the same time, there are other areas where such structures are illegal for public roads.
Are roll cages TIG or MIG welded?
Both TIG and MIG welding can provide welds that are strong enough for a roll cage. Even so, many authorities recommend TIG as it is considered superior.
Are roll cages really worth it?
Yes, they are indeed worth it. And much better than a roll bar. A roll cage protects the driver in the event of a rollover, saving their life.
Is TIG easier than MIG?
Actually, MIG is a lot easier and faster to grasp than TIG. However, TIG welds are cleaner and more precise.
Should I install a roll bar?
No, do not just install a roll bar. A roll bar as a safety product is inferior because a roll bar doesn’t provide as much protection in the event of an accident. A car with only a roll bar will bend and deform more than one with a full safety cage, potentially causing injuries, especially since car occupants don’t always wear safety harnesses or shoulder belts.
The outside surface of a full-cage design has extra welds and tubing for strength, so if you collide from the front (for example), the frame can absorb some energy by flexing before your head makes contact with something hard – something that a roll bar does not do – not good! This is why a roll cage is recommended in place of just a roll bar.