Both roll bars and roll cages are safety devices installed in vehicles, especially race cars, to provide protection for the driver and passengers in the event of a rollover accident. While they serve a similar purpose, there are some key differences between roll bars and roll cages in terms of their design, placement, and level of protection offered.
What is a roll bar?
A roll bar, also sometimes called a roll hoop or rollover bar, is a simple curved bar installed behind the driver that is designed to prevent the vehicle from completely crushing the cabin in a rollover accident.
Roll bars are typically a single bar, or sometimes two bars, that run from one A-pillar (the support alongside the windshield), over the roof, to the other A-pillar. They act as a “roll-over hoop” to stop the roof from collapsing onto the occupants if the vehicle flips onto its roof.
Roll bars are commonly found in convertible sports cars as an essential safety device. They are also frequently installed in off-road vehicles used for activities like off-road racing.
Benefits of roll bars
– Provide basic rollover protection at minimum cost and weight
– Don’t obstruct the driver’s access or visibility
– Easy to install as a simple addition to the chassis
Limitations of roll bars
– Only protect from roof collapse, not side impacts
– Limit driver’s ability to get in and out
– Can obstruct rearward visibility
– Not suitable for high speed crashes
What is a roll cage?
A roll cage, sometimes known as a safety cage, is a more complex tubular structure built around the driver to provide enhanced protection in the event of a crash or rollover.
Roll cages surround the occupants on all sides with multiple bars, bracing, and structural supports. They are typically constructed using steel tubing that is welded together to form a safety cell around the cabin.
More extensive than a simple roll bar, a roll cage provides a full protective frame around the occupants designed for serious racing applications. They reinforce the entire chassis and body shell rather than just a single hoop behind the driver.
Benefits of roll cages
– Provide 360 degree protection in crashes
– Strengthen the chassis against impacts
– Prevent body panels collapsing into cabin
– Allow vehicle to withstand multiple rollovers
– Essential safety for high speed racing
Limitations of roll cages
– More expensive and complicated to construct
– Add considerable weight to the vehicle
– Can make vehicle harder to get in and out of
– Reduce forward visibility for driver
Differences between roll bars and roll cages
While a roll bar and roll cage both provide rollover protection, there are some important differences:
Installation
| Roll Bar | Roll Cage |
|---|---|
| Usually a single bar or hoop added as an addition to an existing chassis | Fully integrated cage surrounding the occupants, welded into the chassis |
A roll bar is relatively simple to install as an addition to the vehicle chassis and requires minimal modification. A roll cage needs extensive installation work fully integrated into the body of the vehicle.
Coverage
| Roll Bar | Roll Cage |
|---|---|
| Provides protection directly overhead but not to the sides | Surrounds occupants on all sides with tubular bars |
Roll bars give overhead protection in a rollover, while a cage provides full coverage around the cabin to protect from side impacts and intrusions.
Suitability
| Roll Bar | Roll Cage |
|---|---|
| Suitable for convertibles and off-roading at lower speeds | Essential for high speed racing and competitions |
Roll bars offer basic protection for street use. Roll cages are engineered for extreme crashes and multiple rollovers in professional racing.
Strength
| Roll Bar | Roll Cage |
|---|---|
| Usually a simple tube framed hoop design | Reinforced tubular steel structure braced for maximum strength |
Roll cages are stronger, strategically braced structures built to withstand high speed impacts from multiple angles.
Visibility
| Roll Bar | Roll Cage |
|---|---|
| Minimal obstruction to driver’s vision | Can partially obstruct forward and side visibility |
The extensive tubing of a cage can block sight lines for the driver, while a simple roll bar has less impact on visibility.
When are roll cages required?
Most race sanctioning bodies and circuits have regulations specifying when vehicles must be equipped with roll cages rather than simple roll bars, depending on factors like:
– Type of racing (oval track, off-road, etc)
– Speed of competition
– Use of harness restraints instead of seat belts
– Convertible or open top vehicles
Some examples of mandatory roll cage requirements:
– NASCAR requires full perimeter roll cages for all vehicles
– FIA regulations mandate roll cages for any convertible competing in circuit racing
– Baja off-road races require cages for all truck and buggy classes
– Many drag strips require roll cages once certain elapsed times are reached
Roll bars are only approved for lower level amateur and club racing where average speeds don’t exceed 100 mph. For wheel-to-wheel professional racing, a full roll cage is generally viewed as an absolute minimum safety requirement.
Key design elements of a roll cage
While designs can vary between vehicle types and racing disciplines, most roll cages share the following essential elements:
Tubing
– Constructed from welded steel alloy tubing
– Tubing is typically 1.5″-2″ diameter with wall thickness of 0.095-0.120″
– Chromoly or DOM tubing offers the best strength-to-weight ratio
Main hoop
– Located behind the driver, follows the roof line of the cabin
– Designed to bear the brunt of impact forces in a rollover
Front pillars
– Run along the A-pillars down to the floor mounts
– Provide roof support and side impact protection
Rear braces
– Join the main hoop to back of the chassis
– Help distribute impact loads toward the rear
Diagonal cross braces
– Connect rear braces to main hoop or front pillars
– Triangulate the structure for stiffness and strength
Door bars
– Run along the length of the driver/passenger side
– Prevent body panels from collapsing inward
Harness bar
– Cross bar for mounting shoulder harnesses
– Often doubles as a diagonal cross brace
Gusseting plates
– Reinforce joints between tubes
– Distribute stresses and reduce bending
Mounting plates
– Bolt or weld cage to reinforced mounting points on chassis
– Spread loads into the vehicle’s structure
Driver extraction
– Quick release doors/windows allowing emergency access
– Sections of tubing cut with saws if needed
Certification and approval
– Roll cages must be certified to meet technical regulations set by sanctioning body
– Needs approval by scrutineers before competition use
– Regular re-inspection required to detect any cracking or faults
Poor construction or outdated designs can lead to cages failing in crashes, often with fatal results. Using an uncertified cage is never worth the risk.
Should you choose a roll bar or roll cage?
Deciding whether you need a roll bar or full roll cage comes down to intended vehicle use and level of competition:
| Roll Bar | Roll Cage |
|---|---|
| Street use convertibles | Dedicated race cars |
| Off-road recreation | High speed track racing |
| Low speed club racing | Demanding off-road competitions |
For serious racing, the choice is clear – a roll cage is a must. Roll bars only provide adequate protection for street-driven convertibles and casual off-roading. If choosing a roll bar, ensure it meets minimum guidelines for dimensions and mounting points specified by the vehicle manufacturer or a racing sanctioning body.
Conclusion
While roll bars and roll cages both provide rollover protection, roll cages are integrated multi-point structures engineered to withstand extreme crashes from all directions. Roll bars offer basic overhead hoop protection for low speed driving. For professional racing, roll cages are an essential piece of safety equipment to protect drivers from serious injury in the event of an accident.