Two Guys Rally

Rollcage As Performance Mod [ July 23rd, 2008 ] By:Charles Smith

Many people tend to think that roll cages only provide safety and some extra weight, but they’re forgetting something: what they can add is stiffness.

Because roll cages were mandated as required safety devices in oh so many racing leagues, clever engineers figured out that they could use them to make their cars better. I don’t know who did it first, but they decided to connect all the suspension points together with a tubular space frame and call it a roll cage. Suddenly the mass of tubes becomes a way to stiffen up the car’s chassis.

You might not realize just how much a normal street car’s chassis flexes under any sort of acceleration (0-60, cornering, braking, etc…). This flexing acts much like the suspension, in fact most go-karts depend on frame flexing as the suspension (also the tires). However this flexing in a normal car changes the geometry of the suspension which can make a car less predictable and much harder to tweak (suspension wise).

Connecting the points where the suspension meets the frame with tubing (aka roll cage) can significantly increase the stiffness of a stamped sheet metal frame. This will keep the suspension geometry closer to normal under hard accelerations and allow you to more consistently judge how your suspension is affecting your car. However in most cars, connecting the suspension points (strut towers) will require to send tubes through the firewall of the car. Do you notice the tubes going through the firewall on the Subaru US Rally Team car? You should not be intimidated by the firewall, cut through it and reseal it around the tubes!

So, if you’re going to add a roll cage, don’t just add it to be within your competition rules. Take advantage of the rules and stiffen up your car so you can better adjust your suspension. Also, it results in less deflection in the chassis, which Mark tells me means you’ll end up with “smaller cyclic loading” on it. That means you’ll have more use of the chassis before it fails from normal race stresses. HOORAY ROLLCAGE!!!