Safety is always a concern when driving, especially if you take any “spirited” drives around mountain touge roads. One way to protect occupant safety is to install a roll bar or roll cage which will add rigidity to a car as well as protect the people inside in case of an accident or rollover. In my accident, I especially discovered kei cars are made of cheap, light metals, so having some protection in my Alto Works will be especially important.

Overview
A roll bar is a simple bar that prevents the roof of a car from caving in, in case of a rollover. You can find aftermarket bars most commonly on open-top convertible roadsters or mildly-modified sports cars used on tracks in non-wheel-to-wheel racing events. In fact, a roll bar is a legal rule requirement for open top cars, as the chance of rollover and roof cave-in are quite high. Certainly, a front windscreen will definitely crush with the weight of a car.

Roll bars are typically simple 2 or 4-point bars that go behind the driver and mount to the chassis of the car. An overly simple 2-point bar is a hoop. While this might be cheap and light, it can be dangerous as it can fold over given enough lateral pressure. It may also be referred to as a “style bar,” as it is essentially more style than safety function. A 4-point roll bar also adds to legs that mount further behind a 2-point hoop, creating 4 points of hard mounting, which will strongly resist any folding should the worst happen. Some roll bars have cross bars that add strength to the whole system.

A roll cage is the next ultimate step in ruining a perfectly streetable car. They are so-called a cage because it essentially surrounds passengers with a metal cage that can protect during a roll-over or from impacts.

Roll cages start at 6-points and increase in complexity and cross mounting points based on safety needs. 6-point roll cages add two arms that go in front of the driver, mounting near the footwell. There are two variants of this, bent arms that follow the curvature of the front dash and through-dash arms. The “standard” bent arms are easier to install, but eat into the cabin space a bit, making ingress and exit a bit more cumbersome. The through-dash cage requires permanent holes to be cut into the stock dashboard or removal of the dash entirely.

While there are nearly infinite designs and options, many cages also offer some cross braces that add rigidity. Some more serious folks who may do wheel-to-wheel racing will add side bars that protect the occupants in the case of a side impact. This isn’t even including the cages that are completely welded in to the chassis.

Material Types
There are two primary materials used in bar construction, mild steel and chromoly. Essentially, both are steel, but have differing weights and strengths. Mild carbon steel is much heavier, but is cheaper to produce and low alloy chromoly is lighter. There are some arguments that claim because mild steel is “softer,” it is more durable after stress or impact, but I don’t know the real facts about that. Racing regulations typically allow either material to be used in cages.

Western or Japanese Differences
In addition, there are further important options to note between “western” and Japanese roll cages. (I am defining them as “western” and Japanese simply for the sake of brevity. There are western companies that follow the primarily Japanese design cues of roll cages and vice versa. Note this also typically only applies to off-the-shelf bolt-in and not custom-designed weld-in.)

In all English standard safety guidelines, the “points” of a roll cage are where the cage is mounted into the chassis. However, companies like Cusco also define those “points” of a roll cage as points where bars cross and connect. Here is a chart from their website. I definitely do not agree with their way of counting points, but I suppose we’re just nitpicking semantics here.

Western companies often minimize the number of bolts used to assemble the cage. Some off-the-shelf companies still require some welding to connect the major hoops of the bars. Unless you are doing professional wheel-to-wheel racing, most Japanese circuit racing rules still allow multi-piece bolted assemblies, which also eases production and shipping costs.

Probably as a result from the more solid design of Western cages, harness bars are often integrated into the cage itself. This results in the more proper harness angle of < 20 degrees from the shoulder, according to many safety harness manufacturers (more in a later post). In the case of a multi-piece bolt-in, I would definitely not trust mounting a harness to it. Hence, typical Japanese harnesses are installed via eye bolts to the rear passenger seat belt mounting points.

Many current racing regulations for cages in the west require 45 to 50mm diameter piping, whereas Japan still commonly uses 40mm. Whether the additional strength and width of the pipes are a necessity is also arguable.

General Advantages
So all these bars are great, but why would anyone want to add a cage? Besides the aforementioned safety advantages in case of a roll-over, having protective bars could prove a literal life-saver in the case of an accident. Keep in mind that kei cars in particular have a thin, sheet metal chassis which will no doubt crumple completely in any higher-speed crash. I’ve seen some post-accident and they don’t look pretty. Undoubtedly the newer models are better designed, but not my Alto. A 21+ year old, lightly rusted car based on a 1980s body will definitely not have such protection.

Beyond the safety aspect, a roll cage will definitely add body rigidity, essentially more than compensating for all those interior braces offered by various manufacturers. This should theoretically aid in handling and minimizing torsional stresses of a flimsy frame.

There is a ton of properly employed safety methodology here. Two guesses as to who the manufacturer of the base car is…

General Disadvantages
Unfortunately, roll cages have plenty of drawbacks themselves. On the flip side of the beneficial safety aspect, a poorly designed roll bar could potentially result in additional injury because exposed bars are extremely dangerous compared to softer plastic interior panels.

Even through-dash types of roll bars compromise interior space and make getting in and out of a roll caged car more difficult, not to mention some cages eliminate the rear seats entirely. This not only reduces passenger and interior space, it is also an issue come shaken time, as the number of passengers can not be changed. (Unless the paperwork is redone, but that is a several hundred-dollar proposition.) Shaken with a roll cage also requires it to be well-padded to pass inspection. (According to sources online. I’ll update this information when I have to shaken again.)

Lastly, a roll cage adds weight, even if it is the lighter chromoly type. This will negatively affect fuel economy, speed, and braking distance. In reality, this weight is probably pretty negligible given that most Cusco cages only weigh 30kg (67 lbs) or less, but in racing (as well as to my little 63 HP kei car), every ounce counts.

For me, the pros definitely outweigh the cons.