Roll Cages - All you need to know

Roll Cages

The definition of a roll-cage is " a structural framework designed to prevent serious bodyshell deformation in the case of a collision or roll-over". But a rollcage is better described as a Rollover Protection Structure (or system). You, the competitor need to CAREFULLY think WHY are you fitting a ROPS to your vehicle. Is it because CAMS or other body said you have to or is it to protect yourself in the event of an accident? If you are only installing because you have to, unfortunately you won't find much support here. There a plenty of hobby and backyard ROPS builders that will sell you the bare minimum ROPS for a discounted price. Unfortunately, you get exactly what you pay for with ROPS manufacturers.

If you answered to improve my own safety, read on an we hope to teach you about ROPS systems and demonstrate why a Rollcage is not always a Rollcage.

The unfortunate thing about the definition of a roll-cage is that predicting the direction and magnitude of the loads encountered by the bodyshell in an accident is very difficult. It is often said by experts in this industry "you tell me how you're going to crash, and I'll design and build you the perfect cage". This is only true if the accident is not TOO big. History shows that even the most comprehensive roll-cages cannot prevent serious injury or fatality in some accidents. The important issue here though is to ensure a minor accident doesn't result in serious injury! The roll-cage structure will also effect the handling and suspension tuneability of the car by stiffening the bodyshell and allowing the suspension to work more effectively.

No matter which branch of motor sport you are about to commence the Roll Over Protection Structure (ROPS) is the most critical of part of the build up. The main things that effect your ROPS and its design and they are; Budget , Weight , Scope of design and intended use of the vehicle (not necessarily in that order though!). Generally your ROPS will end up being a compromise of cost/weight/complexity i.e. A very comprehensive ROPS that is light weight may be relatively costly and similarly if your budget is low a lightweight and basic ROPS won't offer as much protection.

Your first consideration, assuming you have a known budget, is which type of material to use to construct the ROPS. There are currently two types of material currently being used to construct ROPS in Australia. The first choice of material is a 1020 grade mild steel CDW tube which is approved for use by CAMS. The minimum strength of this material is 350MPa (Yield strength) If Roll cage design complies with standard design principles laid out in CAMSregulations then it only requires registration to be used in Australian competition. The second choice of tube is a Chrome/Molybdenum tube of around 650MPa yield strength. This tube is a higher tensile tube which is not approved by CAMS/FIA unless the scope of design is approved by an appropriately qualified engineer. Because these tubes are of a higher strength, clever design will enable the ROPS to be constructed using tubes with a reduced wall thickness. This is where the weight is saved but it must be said that the ROPS design and welding processes of these tubes is more critical.

The next consideration is the design which may be affected by the branch of the sport in which you compete ,budget and type of material. Without doubt the more comprehensive and well designed the cage is, the greater the chance of survival. Most people who wish to enter motorsport or are currently competing will recall some of the huge accidents that have occurred in the V8 Supercars such as Greg Murphy's hit on the tyre wall at Phillip Island or Craig Lowndes multiple rolls at Calder. Both these accidents highlight the security offered by designing the roll-cage as a Safety Cell. Roll-cage design ideologies are constantly changing so what you see in V8 Supercars this year will probably be different next year. It is advised you carefully consider the design as once the cage is constructed it may be very difficult or impossible to change.

Overall view of complex ROPS fitted to Commodore Cup racecar. ROPS manufactured from CrMn and comprises approximately 40 members. Note the horizontal member between the bends of the main hoop and the extensive use of triangulation members and nodes. This car was involved in a major accident at Phillip Island (into the embankment at the hayshed) and there was NO damage to the ROPS or injury to the driver.

Rear side view of Commodore Cup ROPS.

Detailed view of likely head impact areas in ROPS. Note provision of high density padding material and near vertical member from top of A pillar to floor to give upper A pillar support. A window net is required in many categories but is recommended in all as it keeps your limbs etc in the car in a violent accident.

Front ROPS leg support members substantially assist to prevent the crushing of the roof above the driver.

At this stage of your cars construction it is also worth considering strengthening other areas of the body shell. Seam welding (if permitted in your intended category) can stiffen the bodyshell to enhance handling as well as reduce the rate of deformation in an accident. It may well increase the life of the bodyshell over its future years of stress.

As you can see there is much to consider when preparing your car for competition and I hope this article encourages you to think carefully about what may one day save your life!

FabRaications is an established company with the resources of CAMS Technical department, Automotive Engineering experts and other ROPS manufacturers all available. Unbeknown to most people, there is a lot of interaction between all these people about ALL matters involving ROPS. In the case where a vehicle is involved in a major accident, information is shared between these organisations and people to ensure that the industry learns from the accident. Most hobby or backyard ROPS builders are not aware nor conversant with this ongoing interaction and are likely to build your ROPS as they have been doing for the last 10 or 20 years, even though the competition and vehicle developments have been advancing all that time.

The use of nodes to reinforce bent members is critical. Note here the windscreen bar is gusseted to the body and small members are provided from the bends to the front leg. A pillar reinforcement members are attached to this node.

Some things for you to look at when looking at a ROPS:

Does the ROPS use reinforced node points? A node point is a point where ROPS members ALL meet at one point, making the node a point of very high strength.
Are ALL ROPS member bends reinforced? As most members in a ROPS are placed in compression during an accident, it is imperative to reinforce bends in members in order for the member to withstand the maximum possible loads. The usual method of reinforcement of the bends is using nodes or gussets.
Welding and general fabrication - Depending on the material being used on the ROPS, there may be special processes required to correctly weld the ROPS together. ALWAYS check the qualifications and experience of the tradesmen doing the job.
Access to the car - Don't forget that you may need to get out of you car in a big hurry one day and poorly designed or positioned members may create a real problem.
Risk of injury - Always look carefully at where ROPS members are in regard to your seating position as it is possible that you could injure yourself in a relatively minor accident by contacting the ROPS.