What size tubing is used for a roll cage?
In practical terms, most roll cages are built from steel tubes ranging from about 1.5 to 1.75 inches in outer diameter, with wall thickness typically around 0.065 to 0.120 inches. The two most common materials are mild steel DOM and chromoly (often 4130). Exact sizes depend on the car, the class rules, and the engineering calculations behind the design.
Tube materials and typical sizing
There are two main materials used for roll cages, each with typical sizing tendencies. Understanding these helps buyers and builders choose tubes that meet both safety goals and regulatory requirements.
- Mild steel DOM tubing (drawn-over-mandrel): commonly 1.5 to 1.75 inches in outer diameter, with wall thickness typically around 0.095 to 0.120 inches. This option is generally easier to work with and more affordable.
- Chromoly steel tubing (commonly 4130): commonly 1.5 to 1.75 inches in outer diameter, with wall thickness around 0.065 to 0.083 inches. Chromoly provides higher strength-to-weight and is favored for performance-oriented builds, but welding and cost are considerations.
- Aluminum tubings are rare for full roll cages due to different strength and crash-energetics behavior, but may appear in specialized, weight-focused applications. Always verify material choice with rules and a qualified engineer.
These sizes reflect common practice in many racing families and DIY builds, but exact specifications must align with your sanctioning body’s rules and the car’s load paths. Designers may adjust diameter or thickness for space constraints, headroom, and impact requirements.
Choosing between mild steel and chromoly
Choosing between mild steel DOM and chromoly 4130 depends on factors such as budget, weight targets, welding capabilities, and the safety rules of the class. Chromoly tends to yield a higher strength-to-weight ratio, which can allow for lighter cages or additional members, but it is more expensive and requires careful welding and heat treatment. Mild steel DOM is usually cheaper and simpler to weld and replace, making it a common choice for street-legal builds and lower-cost race programs. Regardless of material, all cages should be designed in consultation with a qualified engineer and built to the governing rules of the series in which you intend to compete.
Sizing guidelines by application
The exact tube size used in a roll cage is influenced by the competition rules, vehicle weight, intended speed, and crash safety requirements. The following are common baselines seen in many clubs and series, but always verify with the current rulebooks and an engineer.
- Street and light competition (track days, basic club events): 1.5 inch to 1.75 inch outer diameter tubes, typically 0.095–0.120 inch wall if using mild steel DOM; chromoly options in the same diameter range may use 0.065–0.083 inch walls depending on rules.
- Standard race builds (club and regional series with stricter tech): 1.75 inch outer diameter tubes are common, with wall thickness around 0.065–0.083 inch for chromoly or up to 0.095–0.120 inch for mild steel DOM in some classes.
- FIA-compatible or highly regulated builds: diameter and wall thickness are determined by the specific homologation rules; typical practice centers on 1.75 inch tubes for primary hoops with 0.065–0.083 inch chromoly or 0.095–0.120 inch mild steel DOM, plus carefully engineered cross-bracing and door bars as required by the regulation. Always rely on the official rulebook and professional input.
In all cases, the load paths, headroom, door clearance, and seating position influence tube placement and sizing. A one-size-fits-all number is not appropriate for every car, and an engineer should validate any design before fabrication.
Practical takeaways
For most amateur-to-intermediate builds, expect to see 1.5–1.75 inch diameter tubes, with 0.065–0.120 inch walls depending on whether you’re using chromoly or mild steel. For stricter competition or FIA/Hans-compliant builds, sizes tend to follow the rulebook more closely, often favoring 1.75 inch tubes with chromoly in the 0.065–0.083 inch range, though alternatives exist based on the rules. Always prioritize compliance with your class regulations and engagement with a qualified roll cage fabricator or engineer.
Summary
Roll cage tubing is typically 1.5 to 1.75 inches in diameter, with wall thickness around 0.065 to 0.120 inches. The material choice—mild steel DOM or chromoly 4130—drives exact sizing and weight, and regulatory rules largely dictate final specifications. Always consult the current rules and a qualified professional when designing or purchasing a roll cage for your vehicle.
