You're probably looking at the title to this piece and saying to yourself, "Bracing what?" Well, hold on a minute and allow us to explain. If you're like us, you like to get out in the sand or rocks or mud or whatever you wheel in and have some fun, while looking for a challenge. But before you leave pavement you'll want to ensure your rig has been built to take the abuse you're going to dish out to it.
This means adding strength where strength is needed. So, we'll discuss some of the areas that may need some attention, discuss some of the fabrication options, and show some actual examples of building to survive.
Much of our vehicles are made of metal and when choosing type and size there are several characteristics to consider. Material comes in a variety of shapes. For example you can have round, square, or rectangular tube, or flat strap steel or plate. Each of these has different uses and strength characteristics.
At first it may make sense to make structures as strong as possible to avoid breakage. However, this results in the excessive use of material, driving up both cost and weight. We'd like to minimize both of these where possible. Remember that weight steals speed and places greater strain on parts.
Also, recall that any grouping of components is only as strong as its weakest link, so leaving a substandard part in the chain can cause it to break too easily. Whenever one part is made stronger, you'll need to consider where the next weak point might be. If something breaks, rather than just patching it together and indiscriminately beefing it up, look to see how it failed and what may be the future consequences if something is changed.
Strength In Shapes
Some geometric shapes are inherently stronger than others and can better withstand forces before failure. For instance, when building a rollcage or other structure, there are several ways to configure the individual pieces to make the whole structure. In 'cages, triangles are inherently the strongest shape, and strategic bracing will help ensure vulnerable impact points can take a beating and distribute the force into the structure.
Tubing Strength
How does the size and wall thickness affect how well a tube resists flexing? Much is based on the outside diameter of the tube. Let's take a quick look at some relative strengths of some sample tubing sizes. Say you have a tie rod made of 1-inch-diameter, 0.120-inch-wall-thickness tubing. We'll consider this to have a normalized strength of 1. This represents the force necessary to deflect the tube some distance or the amount of tubing bend as the result of some applied force, such as pushing it against a rock on the trail. The bending strength is a function of (D4-d4), where D is the outside diameter (O.D.) of the tube and d is the inside diameter (I.D.).
| TUBE O.D. |
WALL |
RELATIVE |
|
THICKNESS |
STRENGTH |
| 1" |
0.120" |
1 |
| 1" |
0.250" |
1.4 |
| 1" |
0.500" (solid rod) |
1.5 |
| 1.25" |
0.120" |
2.1 |
| 1.25" |
0.250" |
3.2 |
This table shows the relative strengths of several tie rod size examples. It's easy to see that strength rises with increases in either tubing outer diameter or increases in wall thickness. There are a few interesting numbers to note. First, observe that increases in diameter provide the greatest jump in strength. Just changing the 0.120-inch-wall tubing from 1 to 1.25-inch O.D. more than doubles the strength, from a relative strength of 1 to 2.1.
Conversely, excessive wall thickness increases strength to a lesser extent. Added metal towards the center of the tube axis does less to increase strength than increasing diameter does. Hence, a solid rod is only slightly stronger than a heavy wall tube. Note the relative numbers of 1.4 for 0.25-inch-wall versus 1.5 for a solid rod. There's not much difference in strength, but you can bet the solid rod is heavier, adding unnecessary weight. As we mentioned before, we want great strength but without making everything excessively costly or heavy.
 Consider a tubular cage structure...  Consider a tubular cage structure such as the one shown to the left. A plain square shape such as this offers decent strength but can collapse or distort if hit from a corner. By simply adding an extra tube (middle diagram), the square becomes comprised of two triangles and is much less likely to collapse its shape. An impact such as that shown by the red arrow will tend to spread the impact load across more of the structure, rather than bending the corner. Further, by adding more tubing as shown in the right image, each of the four corners can better withstand impact and the entire structure has been sub-divided into four smaller triangles. |  Tubing is the basic element...  Tubing is the basic element used to build racing chassis and 'cages. When constructing rollcages, the strongest methods are those that can have tube ends merge together at a common junction or node such as the location shown here, and these nodes are often best located at likely points of impact loading or where chassis stresses are high. |  When adding bracing in any...  When adding bracing in any structure, consider the three dimensional benefits of the type you're using. For example, a flat steel plate could have been used to further brace these intersecting tubes instead of the smaller piece of tube shown. However, the tube provides material in three dimensions so the bracing can add more strength over the surface of each tube rather than along a straight, narrow line as a plate would. Additionally, the tubular mating points provide greater weld bead length to better spread the load. |
 This lifted Jeep Cherokee...  This lifted Jeep Cherokee uses a tierod with two bends in the tierod tubing to improve the joint angle at the rod ends. Note that this ultimately weakens a tube in this configuration. With compression forces pushing from the ends, a bent tube is more likely to bend further and collapse than a tube without a bend. This might be a good candidate for the addition of a plate brace spanning a portion of the bend, depending on wall thickness and tubing strength. |  One way to make an assembly...  One way to make an assembly stiffer and add strength where flat pieces are concerned is to use two thin sheets of material instead of one thicker one. Lamination such as that used in this rear suspension arm will make the assembly stronger than if a single, thicker plate was used. |  There was a time when many...  There was a time when many truck framerails were fully boxed on all four sides. But with the recent emphasis on building them to be lighter and lighter, a lot of frames are built from C-channel rails, or boxed over just a portion of the total length. In cases where you'll be increasing tire size and pushing the truck harder off-road, it may make sense to fully box the rails for added strength and rigidity. |
 On this race truck, the coilover...  On this race truck, the coilover shock mounts are welded to a point on the chassis where a number of tubes converge, and an additional tube is bolted onto tabs nearby as well. Bringing all these stress forces together at one point, and from a number of different directions, keeps the assembly much stronger. Note that the shock mount needs its greatest strength in the vertical direction and less in any side-to-side direction. |  Here a structure has been...  Here a structure has been assembled from aluminum sheet to support the fiberglass hood of a race truck. Flared holes are used to make each panel more rigid. Two sheets have been bent and then welded together to form a complex structure in several planes that is very light, while still offering good support strength. |  This serves as a good illustration...  This serves as a good illustration of why a competitive race chassis is so expensive. Many lightweight custom cut sheets and tubes have been combined to build a TIG-welded structure that provides maximum strength with minimum weight in key areas. Straight edges (prone to cracking) are avoided and the curved surfaces and interior holes provide lengthy areas to help increase the weld bead length. |