What is the difference between a “mono tube” gas charged shock and a “twin tube shock”?

-Mono tube shock, also know as a “gas shock,” is designed to operate with the shock oil under pressure. This pressure is housed in a separate chamber, sometimes referred to as a bulb, or an external reservoir. The gas chamber is divided from the oil of the shock often by a floating piston or a rubber bladder. The chamber is charged with nitrogen. The amount of charge pressure is directly dependent on if the shock has an optional base valve and or what compression value the shock is tuned for. (See base valve and charge pressure explanation below). The shock body you see from the outside of the shock is also internally the surface that the piston rides on. This single tube, if dented or damaged, will not allow the internals of the shock to work correctly and often times causes damage to other components.

-Twin tube shock, commonly known as an “oil shock,” also has a gas chamber, but it is often a proprietary plastic bag wrapped around a secondary tube inside of the shock. This secondary tube’s internal surface is the surface that the piston rides on. Twin tube shocks require a base vale to operate. The base valve creates a controlled transfer of fluid from the internal chamber to the area between the outer body and the inner tube. This area is the reservoir to the shock to store oil and the gas bag. Its gas chamber is a fixed value and cannot change so tuning of the base valve is required.

What is the job of the shock ?

In circle track racing, the shock has 2 main jobs:

Traction- If the spring and shock combination is too stiff, then you risk skating across the track surface or bouncing on top of it. If to soft force applied to the tire is less. Both situations involve lowering the effectiveness of the tire and its grip to the track surface.

Control- Shocks help control the amount of understeer and oversteer (tightness and looseness) present in a chassis at particular parts of the track, also known as timing. While the springs hold the car up and at attitude, the shocks can hold or release the spring’s stored energy contributing to specific handling characteristics.

What is “Cavitation”?

Vaporous cavitation is an ebullition process that takes place if the bubbles grow explosively in an unbounded manner as the Air and moisture trapped in the shock oil turn to vapor. This situation occurs when the pressure level goes below the vapor pressure of the liquid. This can happen when there is Low charge pressure or low oil level in the shock. When cavitation occurs you now have air bubbles and vapor traveling through the valving. This will lower your dampening values and change the characteristic of the cars handling.

What is a base valve ?

A base valve is a mechanical device added to a shock that increases pressure to the low speed compression circuit. This device generally is used to lower the mathematical charging pressure requirement for the shock. Often resulting in lower rod pressure , and improved feel from the tire to the track surface.

What is Rod pressure?

Rod pressure or often times called rod force is a physical problem that every shock has to deal with. The shocks internal components ( oil, piston, valving ect) are a fixed value why’ll the shock is extended. Once the shock starts to compress the additional amount of shock shaft now entering the sealed shock creates a displacement problem and begins to add pressure to the system internally that eventually equates to an increased spring rate to the car. Think of a bucket of water full to the rim and you stick your arm in the bucket what happens to the water? it over flows out of the bucket proportionally to the volume of arm you are putting into the bucket. Your shock still contains the oil and the added rod entering it so this displaced volume has to go somewhere. The most common way to deal with this issue is having a larger nitrogen chamber to absorb the displacement issue. The resulting increased spring force ( rod pressure) often times can be a low manageable number that goes unnoticed or it could be a rather high number that causes issues with chassis handling and grip. This data can be calculated or collected by using a shock dyno.

What is a shock dyno

A shock dyno is a piece of testing equipment that allows shock tuners, manufactures and racers the ability to analyze the performance of the shock. This can be to monitor degrading performance over time, to verify a clicker setting, or validate a new build.

What is a spring rate?

A spring rate is a measure of how stiff or soft a spring is. It refers to the amount of force required to compress the spring by a certain distance.

The formula to find the spring rate, often represented as k, for a linear spring is:

k=F/x

Where:

• k is the spring rate (in units like N/m or lb/in).

• F is the force applied to the spring (in Newtons or pounds).

• x is the displacement (how far the spring is compressed or extended) (in meters or inches).

This formula tells you how much force is needed for a certain amount of displacement, which is essentially how stiff or soft the spring is.