Have you observed Cylinder which is attached to rear suspensions in bike?

Why small cylinder is attached to rear suspension?

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The rear shock absorbers on current bikes are popularly known as NITROX shock absorbers. These types of shock absorbers are actually called as ‘Gas Filled Shock Absorbers’. The difference between a conventional shock absorber and a gas filled shock absorber is a small cylinder (canister) which is attached at the top right. This cylinder (canister) holds a small amount of Nitrogen gas in it. So these hydraulic shock absorbers are called as gas-filled shock absorbers.

Spring Loaded Hydraulic Type Suspension

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The conventional spring loaded hydraulic type suspensions work on the principle of Hydraulics. Damper ("A damper is an element that provides resistance in mechanical suspension") works based on ‘fluid’ and in terms of suspension it is the ‘Damping Oil’ that is present in the suspension. The suspension is consists of the outermost spring, which take back the entire suspension unit to its original position after it gets compressed due to the uneven surface.

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The next part comes is the body of the damper which is a tube-like structure filled with Damping oil. Inside the tube, there is the piston for up and down movement sealed by an airtight oil seal. It is this collective damping unit which is responsible for taking the toll of the external jerks.


There are valves fitted to the piston which moves up and down alongside the piston, these valves contain holes and therefore when the piston moves inside the tube filled with damping oil, the oil gets partially compressed and partially it passes out through the holes present at the valves. This controlled movement of piston ensures efficient damping effect which later came back to its original position with the help of spring. This is how a spring loaded hydraulic type suspension works,

The hydraulic oil which is used inside the damping unit after extensive use it starts turning into bubbles(foam) get started. Just like shaking oil in a bottle. Generally some percentage of air present in the oil which gets unbonded with the oil when shaken. These air molecules come out in the form of bubbles and collectively they take the form of foam in later stages. 

In order to solve this, a small cylinder is attached to the shock absorber which stores pressurized nitrogen gas. The pressurized nitrogen gas inside the canister prevents foaming of hydraulic oil inside the damper due to heavy usage or damping action. Due to this, the performance of the suspension remains constant.

This nitrogen gas also helps in absorbing the road undulations and provides a smooth ride for both the rider and the pillion.
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Just take a look at some present bikes having Nitrox Suspensions

Baja RS 200 (Mono-Suspension)

Apache 200 (Mono-Suspension)

Suzuki Gixxer (Mono-Suspension)

Yamaha R15 (Mono-Suspension)

Royal Enfield Mountain (Mono-Suspension)

and many more.