Facts
(or system).
Rollcages are actually a lot more complex than most people think, and as a competitor, you need to CAREFULLY think WHY you are 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 a ROPS for a discounted price. Unfortunately, you get exactly what you pay for.
If you answered to improve my own safety, read on and we hope to teach you about ROPS systems and demonstrate why a Rollcage is not always a Rollcage.
High Safety, Lightweight and Low Price. You can only ever choose two of these.
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. The important issue here though is to ensure a minor accident doesn't result in serious injury! The roll-cage structure will also affect 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.
4130 tube, often called Chrome-Moly, is no lighter than mild steel. A 4130 cage can be built lighter by using thinner members and clever design.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 the Roll cage design complies with standard design principles laid out in the CAMS regulations then it only requires registration to be used in Australian competition. The second choice of tube is a 4130 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 and tested by an FIA approved 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.
Cages are often described by the number of connection points to the chassis i.e. 4point 6 point.
Trouble with this is, if you add two diagonals and a side intrusion bar, it is still a
6 point cage.The next consideration is the design which may be affected by the branch of the sport in which you compete. Without doubt the more comprehensive and well designed the cage is, the greater the chance of survival. 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.
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 one day may 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 neither 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.
FABRaiCATIONS
19 Citrus Street
BRAESIDE VIC 3195
Phone: 613 9587 7772
Fax: 613 9587 0704
