In this latest FOX Academy video installment, we dive into some of the structural, tuning, and ride characteristic differences between a standard shock and our three terrain-tuned series of Jeep aftermarket shocks.
What are some of the main differences between standard shocks and FOX shocks?
Several, actually:
- The intended application and tune
- Steel vs. aluminum body construction
- Consistency and the internal floating piston (IFP)
- Rebuildable and tunable
What’s the intended application of standard shocks?
Standard (or stock) shocks are designed around use on the road, which has very different frequencies and magnitudes of forces than driving off-road.
While your completely stock Jeep is going to be more capable than a sedan (for obvious reasons), it will largely be because of tire size, four-wheel drive, and increased ground clearance, not because the shocks are designed to absorb the higher frequency and larger magnitude forces that come from driving off-road.
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What’s the intended application of FOX shocks?
A FOX shock is intended to be driven off-road. The entire shock is designed and tuned to absorb the higher frequency and larger magnitude forces that come from driving faster off-road.
The intended off-road application is why FOX makes Jeep shocks out of aluminum, uses an internal floating piston (IFP) for consistent performance, and designs them to be rebuildable and tunable so that the shocks can evolve with your Jeep.
Why make the shock body out of aluminum instead of steel?
The standard shocks that come on your Jeep are usually made of steel. Steel is cost-effective and great for insulating. This is one of the reasons why it is used in vacuum-sealed water bottles and travel mugs. Steel keeps hot things hot and cold things cold.
But shocks should not insulate heat; they should dissipate it into the atmosphere. Shocks need to be able to cool down to have consistent performance and comfort, especially when driving off-road.
In addition to its insulating properties, the low carbon steel used on standard shocks has a propensity to rust. To prevent this, a layer of paint is added to help the shock last longer. But the issue with a layer of paint over steel is that it insulates heat inside the shock even more than steel alone.
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FOX Jeep shocks are made of aluminum because 6061 aluminum’s thermal conductivity value is over four times that of low carbon steel. This means that aluminum FOX shocks are able to cool much better than painted steel shocks, and they are extremely resistant to rust.
How can a shock be more “consistent”?
To grasp the concept of “consistency,” you need to know a bit more about the oil and gas inside of a shock.
Shocks use oil to control vehicle movements. The oil also absorbs the heat that is converted from the movement of the shock shaft and your vehicle. In order for the oil to do its job well, it needs to consistently maintain its viscosity in all driving scenarios and temperature ranges. Viscosity is “the state of being thick, sticky, and semifluid in consistency.”
If the oil is too viscous, the shock won’t move enough. Conversely, if the oil is not viscous enough the shock will move too much. In both cases, a vehicle will be uncomfortable and less likely to be in control.
Now, think of a ball being dropped into a full glass of water. When the ball contacts the surface of the water, water flows over the edges of the cup and onto the surface the cup is resting on. This is because the ball entering the cup consumes space previously occupied by the water and it pushes the water out of the way.
Read "Getting to Know Your Shocks"
When the shock shaft enters the shock body, the same type of scenario occurs. But there are two key differences. First, the shock is closed and doesn’t have an opening for oil to flow out of. And second, you don’t want oil to leave the shock body.
To solve this, shocks will use various methods to allow for oil to be displaced. Pressurized gas, coil springs, and expandable bladders are a few examples.
Most shocks will use some form of internal pressurized gas to allow for oil to be displaced by the shaft. As a shock is compressed, the shaft entering the shock body consumes space previously occupied by the oil. To accommodate the displaced oil volume, there is a gas chamber within the shock that is able to compress. During rebound, the gas expands as the oil reoccupies the space that the shaft once consumed.
Now that we better grasp the importance of oil viscosity and the purpose of the pressurized gas, let’s get back to the consistency conversation.
Most standard steel shocks will not have a physical barrier between the pressurized gas and the shock’s oil. When you drive off-road, the higher frequency and greater magnitude forces can cause the shock oil and pressurized gas to mix together.
This is a similar to shaking a half-filled bottle of water. Once you stop shaking the bottle, air bubbles are still trapped inside the water as they travel back towards the top of the bottle where the rest of the air is.
When the shock oil and pressurized gas mix together, the shock oil’s viscosity changes and becomes “not viscous enough.” This is typically because the oil will foam or trap bubbles of gas. When oil is not viscous enough, it does not provide enough resistance against the piston assembly on top of the shaft as it moves through the oil. The resistance between the oil and the piston assembly is what controls the movements of your vehicle to provide comfort.
Without a barrier between the shock oil and pressurized gas, the shock becomes much less effective at controlling the movements of the vehicle during compression and rebound, especially when driving off-road.
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When we say “controlling the movements of the vehicle,” we mean controlling oscillations. If you’ve ever hit a bump and noticed the front or back of your vehicle continue to bounce up and down after the initial impact, this is a sign of lack of control. The shock is not applying the right amount of damping force to bring the body of the vehicle back to rest after absorbing the impact.
A “less consistent” shock is one that is not able to maintain its effectiveness at controlling the movements of your vehicle while driving off-road. A standard shock is less consistent than a FOX shock.
An IFP is a barrier between the pressurized gas and the shock oil that prevents the two from mixing and foaming. All FOX Jeep shocks have IFPs because they prevent oil from foaming and ensure consistent performance over long, hard, and fast miles off-road. The IFP allows your FOX shocks to maintain their effectiveness at controlling the movements of your Jeep and ensuring your comfort.
If you want to learn more about IFPs, oil, compression and rebound adjustments, and the specifics of “how a shock works,” we’ll be releasing videos and posts on these topics soon.
Like what you see? Check out all the FOX Academy videos for powered vehicles and mountain bikes here.
