Front fork oil level adjustment

Front fork oil level adjustment

Adapt the behaviour of your forks using the right oil level for your needs

On many occasions we receive inquiries asking about the amount of oil to pour in a particular fork. And although there is an approximate amount recommended by the motorcycle manufacturer, we never recommend using a certain amount of oil, because it is inaccurate and ineffective.

The oil usually sticks to the tubes walls, internal components and inner tubes. So even if they have been emptied, you can never get the same amount of oil in both bars.

Even if a fork has been completely disassembled and reassembled, without a single drop of oil remaining inside, when pouring the oil inside, you will never pour exactly the same amount. And in this application 0,18 oz DO make a difference.

Instead, we always recommend measuring the level with a syringe and a level gauge specifically for this setting. It is as simple as pouring the oil, bleeding the hydraulic and removing the excess with the syringe.

Jeringuilla de nivel para horquillas delanteras. Útil imprescindible para ajustar la cámara de aire de manera precisa.
Example of a level syringe. Adjust the stopper to the desired level measurement and pull the syringe stem to suck out the excess. Easy, simple and a very affordable tool.

But what is the importance of adjusting the oil level?

A lot, and you can play with it to adapt the behavior of the fork at the end of its travel.

The air chamber left inside the bars, from the oil level to the cap, acts as a secondary spring. It is like a spring stacked on top of the coil spring, which as a result provides the sum of both springs.

The difference is that, being air springs, it has a greater progressivity and is harder at the end of the stroke, which is when the air is more compressed due to the smaller size of the air chamber (since the space is smaller due to the compression of the fork leg).

Because of this characteristic, the oil level can be played with according to our riding preferences.

Gráfico que muestra la progresividad de la cámara de aire en función del nivel de aceite en su interior.
This graph shows the difference in the behavior of the air chamber as a function of its height.
Note that it begins to have a noticeable influence from about 80% of the travel.
The graph only illustrates the influence of the air chamber, remember that this force should be added to that of the coil spring.

Imagine that you have the right pair of springs for your riding, the preload is adjusted to the inch and the hydraulics are working within their correct range of operation, but in the hardest braking of the circuit the fork has practically no travel and there is a danger of bottoming it out.

What to do?

Replacing the springs for a stiffer ones? Increasing the spring preload? Closing the compression damping?

The ideal option in this case is to add some oil to the inside of the forks. This way the air chamber above the oil level is smaller, so the air trapped inside will be compressed faster and offer more resistance before the end of the stroke.

This means that the higher the oil level (larger air chamber) the less force this air spring will exert at the end of the stroke, while the lower it is, the more resistance it will offer under equal conditions.

Ajuste de la altura de aceite en una jeringuilla de nivel
Adjusting the oil height measurement on a level syringe.

Check out in the following link how affordable those level syringes are:

Let’s give you another example. Imagine that you are on a circuit that does not have excessively hard braking and you see that you are not using the entire suspension stroke.

What would you do this time?

The simplest way would be to remove (with a syringe) a certain amount of oil, in order to increase the volume of the air chamber and obtain less resistance at the end of the stroke.

Please note that this setting does not replace the correct spring setting, preload (SAG) setting or damping setting; it is simply another fine adjustment that can be used depending on the type of riding and the track.

Want to learn more about suspension adjustment? Buy our “Motorcycle Geometry and Suspension adjustment” book. Order it now clicking here!

In summary: the air chamber acts as a secondary spring on any fork, provides a progressive feel as the fork travel increases and can be used as a “fine” adjustment (5 by 5ml for example) to suit specific track conditions allowing the use of the full travel of the front suspension.

Pro tip: Remember to always make small changes. One at a time.

So, from now on change “How much oil do I put in my fork?“for “What’s the oil level for my fork?”

What type of oil do I use? Check our suspension oil weight chart here


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