Suspension

Your vehicle’s springs hold the vehicle weight and set its ride height, while the shock absorber controls the motion of the spring during compression and rebound; keeping the tires planted firmly on the road. Both components are designed to work together, so the changing of a spring’s specification should also require the changing of the shock absorber that controls it.

For example:
Increasing the spring rate so that it is capable of carrying more load will require the shock absorber to be valved so that it can handle the increased forces of the rebounding spring while also providing controlled compression. Increasing a spring’s length for greater ride height will require lengthening the shock absorber body and possibly lengthening its range of travel in order to prevent the topping or bottoming of the shock absorber.

All shock absorbers need some amount of airspace to allow the hydraulic fluid to expand and move properly, however, when the air mixes with the hydraulic fluid, it can cause it to aerate (foam) and therefore lose damping effectiveness. This most commonly happens in standard hydraulic shocks.

Nitrogen gas is used to replace air within a shock absorber to help control the flow of hydraulic fluid (this is because it is not readily absorbed into the fluid like air). Various shock designs do this differently.

Within a twin-tube shock, the gas sits in the reserve tube to keep pressure against the fluid as it passes through the valving and prevents it from being dumped into the reserve tube.

A mono-tube shock uses a floating piston at the base of the piston bore to separate the hydraulic fluid from the gas, also preventing aeration. This design, however, reduces the travel of the piston within the shock body, affecting the overall travel of the shock.

Like a mono-tube shock, the external canister in a BP-51 utilizes a floating piston to separate the hydraulic fluid and gas, however, it is contained within an external reservoir so as not to cause a restriction on the shock travel. The reservoir is large to handle the increased fluid volume in the shock and is remote mounted to aid fitting. Additionally, it can also help cool the hydraulic fluid as it is routed away from the hotter moving internal components.

Traditionally, the bypass shock design incorporates a number of tubes that run external of the shock absorber body in order for the hydraulic fluid to bypass the internal piston.

This design has prevented bypass shocks from being incorporated into everyday vehicles without expensive modifications due to dimensional constraints; especially modern coil-over independent suspension. BP-51 uses a unique extruded alloy body where the tubes are replaced by passages within the shock absorber body, allowing it to fit into tighter confines such as inside a coil spring.

BP-51 stand for bypass 51mm diameter bore.

Bypass shock absorbers have been used in off-road racing for many years and are renowned for their ability to handle the toughest terrain and endure through the harshest abuse.

While most shock absorbers use velocity sensitive damping (meaning the faster the shock absorber compresses and expands, the higher the level of damping force is), bypass shock absorbers take this to the next level by also generating damping dependent on the position of the piston within the shock absorber body.

Bypass refers to the ability of the hydraulic fluid to bypass the piston by being routed externally to the shock bore; creating a high level of comfort initially but increasing the damping forces as the shock reaches the end of its travel in both compression and rebound. In Old Man Emu BP-51 shock absorbers, the amount of bypass is adjustable so that it can be tailored to suit different terrain, speed and loads.

Shock absorbers come in all shapes, sizes and designs – from the outside it’s hard to know what’s what!

Mono-tube shocks are common in aftermarket 4WD suspension, by design they offer less travel for a given external length and can be more prone to failure if impacted by rocks and debris off-road; a dent to the single tube can damage the internal components.

Old Man Emu Nitrocharger Sport is a twin-tube design with the outer reserve tube providing protection to the internal components off-road. Utilizing the latest advances in shock absorber technology, Nitrocharger Sport is the most finely tuned 4×4 shock absorber on the market.