Merriam-Webster’s Dictionary defines articulation as follows …
1 a : a joint or juncture between bones or cartilages in the skeleton of a vertebrate
b : a movable joint between rigid parts of an animal
2 a : the action or manner of jointing or interrelating
b : the state of being jointed or interrelated
3 a : the act of giving utterance or expression
b : the act or manner of articulating sounds
One may be wondering, “What exactly does this have to do with Jeeping?” Well today we’re going to be focusing on ole’ Webster’s second definition here and how the vehicle’s ability to flex and move relates to its capability on the trail. The theory is simple: the more your wheels can travel up and down the more likely all 4 wheels will be touching the ground. As we discussed recently, most vehicles will transfer torque to the path of least resistance (open differential), and if a tire ever leaves contact with the ground, that axle will cease to be effective in moving the rig forward. But how do you know how much articulation your vehicle has and how can you improve it?
The number one factor that affects the amount of articulation is suspension design. These can be divided into two major categories: Independent and Solid Axle. The solid axle design is as old as the horse and buggy, with the independent designs being a lighter weight, modern, and better performing in most everyday driving situations. The independent suspension has become the standard of the industry for most modern 4 wheel drive vehicles. The biggest downside to the modern independent suspension is its lack of wheel travel. While independent systems can be modified to have a much greater level of articulation, the old-fashioned solid axle systems are generally considered the best for off-road capability.
Modifying for Articulation
Many aftermarket suspension systems are designed to increase wheel travel dramatically. Key components include longer control arms, longer shocks, flex joints, and sway bar disconnects. Contrary to common belief, a lift kit alone will not increase wheel travel, and can sometimes reduce articulation due to stiffer springs. The single most effective component to increase flex is the sway bar disconnect. The sway bar is a piece that helps the vehicle corner well, but inhibits wheel travel. Disconnecting it can often double the articulation.
So how do you know how much your vehicle can flex? The test is simple. Drive one wheel up a ramp as far as you can go until one of the other wheels starts to lift off the ground. The distance traveled up the ramp is then measured and divided by the vehicle’s wheelbase, then multiplied by 1000 to give a final number called a Ramp Travel Index (RTI) score. Typical RTI scores can range between 300-1000 points.
Our club, the CSC4W, had our 4X4 kickoff get-together this past weekend. We had 23 vehicles try out the ramp, and they scored a low of 238 and a high of 880, respectively. The low scoring vehicle was a Nissan pickup with a stock front independent suspension; the top performer was a buggy with a custom, long-travel suspension and solid axles. I scored 3rd, with score of 688 – a very impressive score for a mildly modified TJ Wrangler!
Knowing how flexible your vehicle is, is crucial to understanding its overall capability. Check it on a RTI ramp when available, then test it to see what may be inhibiting wheel travel. With a little trial and testing you can help modify your vehicle for maximum articulation.