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So, you've decided that the white shocks aren't cutting it anymore. Well, congratulations and welcome to the family. A lot of this info (and all the pics) was borrowed from Bill Vista's Coilover Bible on Pirate4x4. Read the whole article for more info that I left out for simplicity's sake.
Let's start with the basics. A shock absorber is basically a hydraulic piston pump that converts the energy of motion (kinetic energy) into heat energy. One end of the shock, the shock body or “tube”, is the cylinder of the pump, the other end of the shock is the rod and piston. One end of the shock is connected to the chassis and the other end is connected to the suspension. As the wheels move up and down relative to the chassis the piston pumps up and down in the cylinder.
Because of the valves and the fact that the piston orifices are so small, only a small amount of fluid, under great pressure, passes through the piston as it pumps up and down. The resulting resistance slows down the piston and creates heat from friction. This in turn slows down spring and suspension movement and converts the spring’s kinetic energy to heat in the oil that is then dissipated as the oil cools.
The amount of damping a shock absorber provides depends on the number and size of the orifices in the piston as well as the valving. By changing the design of the valves, the pressure at which they open and close can be altered and a shock’s damping characteristics can be tuned as needed. The higher the opening pressure, the firmer the shock. The lower the opening pressure, the softer the shock.
Shocks work in two directions- compression and rebound. Compression (which only holds unsprung weight- axles, tires, etc), and rebound (which holds the entire vehicle's weight). This is why shocks are made to have more resistance during compression than rebound (Ex. 255/70, 170/60...) Obviously custom valving comes into play for uber-lightwight buggies running giant heavy axles/tires.
The cylinder (shock body) is a tube filled with hydraulic oil. When the piston pumps up and down through the hydraulic oil, the oil is forced through holes in the piston, called orifices. The flow of the oil through the orifices is further regulated by the deflection of special spring-loaded metering valves, or deflection discs, located on either side of the piston.
It doesn't take a rocket scientist to figure out that all this oil flowing through the shock at a high rate of speed through tiny holes is going to create heat. When the oil heats up, it gets thinner (duh) and thus flows more easily. When it comes to shocks, this is a bad thing, the thinner oil allows the shock to compress and extend with much greater ease, worsening the control you have on your vehicle. This is called "shock fade." More on this later.
You'll often see shocks that are "Nitrogen Charged" that are usually a few dollars more than the cheapo hydro ones. The nitrogen is there simply to help prevent cavitation and aeration of the shock oil. When the shock cycles, it creates an area of low pressure behind the piston, and the oil risks changing from its liquid to gas state- cavitation. And when this happens, air bubbles can form in the oil - aeration. This process happens faster the faster the shock cycles, and if the shock doesn't have a chance to cool, the oil turns to a foam and loses a lot of it's ability to dampen. In extreme cases the shock is turned momentarily useless. The gas is used to prevent these pressure changes, and fight shock fade, as well as allow for improved valving.
Now, mono-tube or twin-tube? Well obviously the more expensive ones are monotubes so they have to be better, right? Yup. Twin tubes are popular because they're cheap to make, can be made very compact,and their flaws aren't necessarily a bother in 90% of their application. Most cars on the road have twintube shocks. Twin tube shocks have essentially two tubes, or rather, a tube within a tube. The oil is displaced to the outer tube during compression, and in nitro twintube shocks, that is also where the 100-150psi of gas is stored. Twintube shocks use a base valve AKA compression valve at the bottom of the shock to control fluid movement during the compression stroke of the shock by metering the flow between the pressure tube and the reserve tube. Since the outer tube blocks the inner tube, it prevents the shock from being adequately cooled.
Monotubes have only one tube (genius nomenclature), and are longer than twin-tube shocks because the single pressure tube must have sufficient length to store the hydraulic oil that is displaced as the rod travels into the pressure tube as well as provide space for the fluid as its volume expands due to heat during use.
Monotube shocks are gas charged, so they must also have a place to store this high-pressure nitrogen. There are two methods of accomplishing this. In some shocks, the nitrogen is stored with the oil in the pressure tube. The gas and the oil are, in effect, mixed together in an emulsion. This style of gas-charged mono-tube shock is known as an emulsion shock (again, genius nomenclature). The better way to store this gas in an external reservoir. The reservoir not only keeps the shock cooler, but allows the body of the shock to be MUCH shorter. Instead of a base valve, all of the valving in monotube shocks during both compression and extension takes place at the piston. Since the piston and rod are easily removed from the shock, the monotube design can be taken apart, rebuilt, and re-valved by the consumer, provided you have someone to charge it with nitrogen.
Another benefit of the monotube design is that the shock oil is in direct contact of the outside body of the shock, allowing for much better cooling characteristics, as the shock body act as a heatsink.
Lastly, a side-to-side comparison:
Now you are informed as to why either,
A: Your shocks suck
or fortunately
B: Your shocks rock
Hopefully, the answer is B, otherwise I will laugh at you and your boiling hydraulic oil when you choose to drive quickly over uneven terrain.
Adam
Let's start with the basics. A shock absorber is basically a hydraulic piston pump that converts the energy of motion (kinetic energy) into heat energy. One end of the shock, the shock body or “tube”, is the cylinder of the pump, the other end of the shock is the rod and piston. One end of the shock is connected to the chassis and the other end is connected to the suspension. As the wheels move up and down relative to the chassis the piston pumps up and down in the cylinder.
Because of the valves and the fact that the piston orifices are so small, only a small amount of fluid, under great pressure, passes through the piston as it pumps up and down. The resulting resistance slows down the piston and creates heat from friction. This in turn slows down spring and suspension movement and converts the spring’s kinetic energy to heat in the oil that is then dissipated as the oil cools.
The amount of damping a shock absorber provides depends on the number and size of the orifices in the piston as well as the valving. By changing the design of the valves, the pressure at which they open and close can be altered and a shock’s damping characteristics can be tuned as needed. The higher the opening pressure, the firmer the shock. The lower the opening pressure, the softer the shock.
Shocks work in two directions- compression and rebound. Compression (which only holds unsprung weight- axles, tires, etc), and rebound (which holds the entire vehicle's weight). This is why shocks are made to have more resistance during compression than rebound (Ex. 255/70, 170/60...) Obviously custom valving comes into play for uber-lightwight buggies running giant heavy axles/tires.
The cylinder (shock body) is a tube filled with hydraulic oil. When the piston pumps up and down through the hydraulic oil, the oil is forced through holes in the piston, called orifices. The flow of the oil through the orifices is further regulated by the deflection of special spring-loaded metering valves, or deflection discs, located on either side of the piston.
It doesn't take a rocket scientist to figure out that all this oil flowing through the shock at a high rate of speed through tiny holes is going to create heat. When the oil heats up, it gets thinner (duh) and thus flows more easily. When it comes to shocks, this is a bad thing, the thinner oil allows the shock to compress and extend with much greater ease, worsening the control you have on your vehicle. This is called "shock fade." More on this later.
You'll often see shocks that are "Nitrogen Charged" that are usually a few dollars more than the cheapo hydro ones. The nitrogen is there simply to help prevent cavitation and aeration of the shock oil. When the shock cycles, it creates an area of low pressure behind the piston, and the oil risks changing from its liquid to gas state- cavitation. And when this happens, air bubbles can form in the oil - aeration. This process happens faster the faster the shock cycles, and if the shock doesn't have a chance to cool, the oil turns to a foam and loses a lot of it's ability to dampen. In extreme cases the shock is turned momentarily useless. The gas is used to prevent these pressure changes, and fight shock fade, as well as allow for improved valving.
Now, mono-tube or twin-tube? Well obviously the more expensive ones are monotubes so they have to be better, right? Yup. Twin tubes are popular because they're cheap to make, can be made very compact,and their flaws aren't necessarily a bother in 90% of their application. Most cars on the road have twintube shocks. Twin tube shocks have essentially two tubes, or rather, a tube within a tube. The oil is displaced to the outer tube during compression, and in nitro twintube shocks, that is also where the 100-150psi of gas is stored. Twintube shocks use a base valve AKA compression valve at the bottom of the shock to control fluid movement during the compression stroke of the shock by metering the flow between the pressure tube and the reserve tube. Since the outer tube blocks the inner tube, it prevents the shock from being adequately cooled.
Monotubes have only one tube (genius nomenclature), and are longer than twin-tube shocks because the single pressure tube must have sufficient length to store the hydraulic oil that is displaced as the rod travels into the pressure tube as well as provide space for the fluid as its volume expands due to heat during use.
Monotube shocks are gas charged, so they must also have a place to store this high-pressure nitrogen. There are two methods of accomplishing this. In some shocks, the nitrogen is stored with the oil in the pressure tube. The gas and the oil are, in effect, mixed together in an emulsion. This style of gas-charged mono-tube shock is known as an emulsion shock (again, genius nomenclature). The better way to store this gas in an external reservoir. The reservoir not only keeps the shock cooler, but allows the body of the shock to be MUCH shorter. Instead of a base valve, all of the valving in monotube shocks during both compression and extension takes place at the piston. Since the piston and rod are easily removed from the shock, the monotube design can be taken apart, rebuilt, and re-valved by the consumer, provided you have someone to charge it with nitrogen.
Another benefit of the monotube design is that the shock oil is in direct contact of the outside body of the shock, allowing for much better cooling characteristics, as the shock body act as a heatsink.
Lastly, a side-to-side comparison:
Now you are informed as to why either,
A: Your shocks suck
or fortunately
B: Your shocks rock
Hopefully, the answer is B, otherwise I will laugh at you and your boiling hydraulic oil when you choose to drive quickly over uneven terrain.
Adam
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