Rollcage

Rollcage building

This is a major undertaking and will require careful attention to get it right. First step is to check the rule book, but basically if you follow the FIA rules you will pass with any organization. Try to get in contact early with the scrutineer of the sanctioning body that will inspect your cage and issue a logbook so that your design choices can be valdated along the way.

You can try to do the cage yourself if you have a bender, tube notcher and appropriate welder and skills. It is usually cheaper, faster and safer to let a professional do the work, there is still plenty to do on the car besides the cage. The cost of a cage will vary depending on the complexity of the cage and how much stripping of the car you did (prices range from ~1000$ to 6k+$). Don't expect to go with a cheap bolt on cage, you need a welded in cage. Seam welding the chassis could also be a good option.

The cheapest option is to entirely strip the car yourself (remove all the interior parts, dashboard, wiring, etc... anything that is in the way of building the cage) which also sometimes require removing the front windshield and/or the roof of the car.

Come up with a detailed plan of what you want for a rollcage, provide pictures from existing builds and a copy of the rules to your builder to show exactly what you want. Here are a few examples::

• • Corvette rollcage design document  (note this is a road racing cage, not compliant for rallying): https://drive.google.com/file/d/0BzRipEXLp5msbG13SUxJdFFmODg/edit?usp=sharing

  • Subaru rollcage design example from http://www.hotrodjim.com/service_roll_cage.php (note that the sketch below does not show the required gussets)

  • Audi RS4 rollcage design document: https://tinyurl.com/33m7y29u

Once you have come up with a design, consult with the scrutineer who is going to issue the logbook to make sure he is ok with the design. Keep him updated during the build process too so that he can spot any issue before it is too late to fix them.

You can also check the North America Rally Cage Builder Map to find a fabricator near you: https://www.google.com/maps/d/viewer?mid=zP97LPvuElJ4.k55vLkhn6mps&hl=en_US

There are a number of factors to consider when building a cage like weight, clearances with occupants, ease of egress, reinforcement based on original chassis stiffness, etc... Here is an excellent video showing tradeoffs and analysis of the deformation of the cage:

Tubing material

The FIA requires Cold drawn seamless unalloyed carbon steel (CDS) tubing for rollcage construction (see table below for specs). they also specify 'In selecting the steel, attention must be paid to obtaining good elongation properties and adequate weldability'. 

Typical cage design for a new build

The base structure of the cage has to follow one of the 3 basic structure designs with 253-3 usually being the preferred design (see picture below). The cage is fixed to the chassis to 6 mounting feet, a main rollbar, a main rollbar (in red), 2 lateral half-rollbars (in blue), a transverse member over the windshield (in yellow) and 2 backstays (in green).

The next step are the diagonals in the main rollbar which are mandatory for all new builds and most grandfathering rules. The choice of backstays depends on your choice of roofbar., The FIA regulation is confusing because the rules are also provided for series that don't use a codriver. The mandatory 253-20 bar is mandatory if you don't have a codriver but for stage rally with a codriver you will need either 253-21 or 253-22 which will pair with roof bar designs 253-12 and 253-14 respectively.  See in the next section why we think no one should build a cage with a 253-13 design.

The 253-13 roof bar design does not offer any support in the front roof corners where impacts are most like to happen in case of a rollover or impact with a leaning tree. Here is an example of an incident at a US event (100 Acre Woods) where a relatively low speed impact with a tree caused the cage to collapse. Despite the windshield support bar, the lack of a roof bar in the corner to counteract the forces applied to that corner of the cage compromises the cage integrity immediately. Also note that in this case, the front lateral was not gusseted to the A pillar. 

We think that this roof design should be banned and if you buy an already caged car with that design, think about upgrading it with a 253-12 or 253-14 design (see the section on buying an already caged car below)

Doorbars

The door bars must be at least two bars and the design must be the same for driver and codriver, no asymmetrical design like for road racing. Some sanctioning bodies have a mandatory requirement for the sill bar (the bar in red in the 253-9 drawing below:

Winshield reinforcement bar

The windshield reinforcement bar is now mandatory in all cases for ARA, for most cars it is required anyway, Just make sure the bottom of the bar is less than 100mm from the foot of the cage (see 253-52 on where to measure). This is a common issue if the mounting plates are on the floor and the doorbars are relatively high. It is much easier to reach the monimum distance if a box is used for the footing of the cage.

Optional bars

A number of optional bars are common but depend on the car configuration:

• 253-17: often used to transfer the forces from the door bars to the rear strut towers

• 253-18: often used to limit the flex of the chassis between the strut towers and rear side impacts

• 253-25: also called anti-intrusion bars, they must connect to the top of the front strut towers

• 253-29: the dash bar is optional and oftentimes it is easier to retain the factory dashbar and weld or gusset it to the laterals. But it is sometimes better to upgrade the dashbar and integrate it to the rollcage.

• 253-31: those extra reinforcement gussets often referred to as temple bars are pretty common, there are however dimension restrictions as mentioned in the next section.

Dimension constraints

One of the most common mistake in the bar design is the door bar being too high in the door opening (must be less than half of door opening) or the temple bar attachment points (see dimensions A, B and C in the 253-49 drawing below).

Rollcage padding

Rollcage padding is required on all the roof bars (see drawing below from ARA rule that mimics the FIA rules). Also think about protecting your elbows from the door bars by preserving as much as you can from the stock door cards. Think about using dual durometer padding (https://www.rollbarpadding.com/product/id-38) on bars that you could hit with your arms.

 (~$20 for 3ft, plan on 15 ft for a good coverage): SFI rated mini-padding where the helmet can reach the bars (http://www.jegs.com/i/Allstar+Performance/049/ALL14112/10002/-1), high density padding for door bars, winshield bar and bottom of a-pillar reinforcement bar (http://www.jegs.com/i/Longacre+Racing/441/65162/10002/-1). You might find cheaper padding from Pegasus (https://www.pegasusautoracing.com/productselection.asp?Product=2395)