I have a rockshock air fork on my bike and it feels too firm. The compression is on the softest setting I believe so opposite to the lock symbol (see photo) so I think this means that it will compress the most it can but I am not 100%. So I am 45kg (14 years old). So I am asking if it feels too firm do I need to let some air out of it and if so do I need to get a specific shock pump? Thanks
Yes, you will need a shock pump. They have a screw on head that you don't get with a track pump. They also have a narrower barrel which allows you to deal with the high pressures often found in rear suspension.
It's very likely at 45kg you will need to reduce the pressure in your fork. I find that even at 60kg it can be tricky to get suspension setup well as it is typically designed around a more 'normal' 75-80kg rider.
You can indeed somewhat affect the "firmness" feeling of an air fork by changing the air pressure inside it. However, this is not a primary mechanism for controlling compression damping, as it has side effects. Reducing air pressure will also increase static sag of your fork, meaning that you will end up with less usable travel. The fork will simply become shorter when you rolling on a flat.
The compression damping is primarily controlled by a separate hydraulic circuit in the fork. In simple terms, it is sticky oil that flows back and forth through a hole. A larger hole or less viscous oil will mean that the fork legs can move faster. Closing the hole (with the control knob you see) makes the hole smaller, thus increasing the firmness feeling.
Range of achievable variation in compression for given damper construction is always limited. You cannot make it compress infinitely fast. If you want to set it outside the available range, it can only be achieved by modification to the damper unit. That is quite advanced and expensive fork modification.
A few recommendations.
- Make sure you set up the air pressure so that the sag is within manufacturer's recommendations. Aim for larger sag (say, 30%) and check if it fits your needs. There are many tutorials on the web on how to do that.
- Yes, you need a special high pressure pump for that. Regular tire pumps are not designed to operate on suspension forks. Attempting to ignore it is like to try towing with a car where a tractor should be used.
- The front tire also plays role in how firm the ride feels. Try reducing the front tire pressure a bit.
- Make notes to see what adjustments you tried (what pressures in fork, tires and etc. settings) and how they felt. It will take a few iterations to figure out the best settings, or find yourself at the end of the adjustability ranges.