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MTB Suspension Sales, Service & Support

What are all these adjusters?

Posted on August 16 2017

There are basically three main common types of external adjustment on most suspension forks and shocks. By going through them all in a little more depth and explaining what they are, what they do and how they can affect your ride, will benefit your setup and subsequently your riding experience.
1) Spring/Preload - This is the adjustment of either a spring pre-loader knob or spring rate (coil forks) and preload collar (coil shocks), or, most commonly It is the adjustment of the air spring pressure. This is adjusted using a shock pump, and allows us the selection of particular pressure setting based on weight via either the manufacturers recommendation, or via a basic setup with the rider (see further on for more on this). The benefit of an air fork or shock is that they are generally pretty user friendly to modify to suit rider preference. Not only can you easily adjust your air spring pressure by using a shock pump, you can also change it's rate of compression by modifying the volume of the air chamber within with variations of volume spacers (in basic terms). For forks these are sometimes referred to as 'tuning pucks' or 'bottomless tokens', and for most shocks there are air volume spacers and varying volume air cans.
Here's what they can do:
- Installing air spring volume spacers can effectively reduce the amount of air volume inside, which in turn will make the fork or shock feel more progressive and 'ramp-up' sooner in its travel, reducing its likelihood of bottoming out. This is common in shorter travel forks and shocks, especially those being used for X-Country riding and racing with 80-100mm travel, although they also can be used in longer travel forks or shocks to achieve a more progressive feel.
- Removing air spring spacers can increase the volume of air inside, createing a more linear rate of compression that can feel plusher, easier to bottom out and even more sensitive for small bump compliance, although it can adversely affect the performance of the fork or shock if the spring rate or pressure setting is not spot on. The removal of these types of air spring spacers, and effectively increasing the volume of the the air chamber is reasonably common for lighter riders (Less than 65kg) struggling to properly 'use' all that fork or shock travel they have on board. Another way of achieving a more 'linear' and or 'bottomless' feel in air sprung rear shocks can be by using a higher volume air can, which is a popular aftermarket upgrade for even older shocks with several options now available for most brands. Another benefit of a larger volume air can is often an increase in the small bump sensitivity of the shock, especially when that additional volume is found in the negative chamber, such as the Fox Evol for example, which is a fantastic upgrade for many older Fox Float models).
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2) Compression: This is the adjustment of how firm or soft a fork or shock will travel throughout its stroke. Compression damping adjusters control the fork or shocks speed at which it compresses as it hits a trail feature or obstacle and can have a massive impact on how a fork or shock rides, regardless of if the accuracy of the air spring pressures. Compression adjusters control the flow of oil through the internal damper's shim and piston assemblies. In basic terms, the thinner the shim stack, and the wider the mouth or 'holes' in the compression piston, the easier it will be for oil to flow and the fork to compress. This is one of the most commonly modified part of a suspension fork or shock and is done internally by reconfiguring the compression shim stack within the fork or shocks oil damper system. Sometimes, the rate of compression is also adjusted by using differently weighted oils inside the fork or shock. For example: A heavier oil will flow through the piston harder and slower than a lighter weighted oil, therefore a heavier rider wishing to increase the rate of compression without modifying the internals may consider a heavier weighted oil, and vice versa.
In many cases, there are adjustments for 'high speed' compression, and adjustments for 'low-speed' compression. But what's the difference? 
  • High speed compresison (HSC) adjustment controls the fork or shock's movement under a fast or sudden impact such as hitting a rock or root mid trail, or the heavy landing off a jump. It is an adjustment more commonly found on longer travel forks and shocks to control the stability of the bike during the sudden impacts and consecutive hard hits.
  • Low speed compression (LSC)  adjustment controls the fork or shock's movement under general pedalling forces, small bumps including trail surface undulations and even braking. LSC adjustment is more commonly found as an external adjuster than it's high speed counterpart, and it is also commonly found on forks or shocks with a multiple position compression adjuster/lever. This generally allows the rider to choose between soft, medium and firm LSC settings depending on the terrain or style of riding.
For example, The Fox CTD (ClimbTrailDescend) 'Trail Adjust' range of forks and shocks allows you to fine tune the 'Trail' setting, which is allowing you to externally customize how soft or firm you would like the LSC stroke to feel in that middle 'Trail' position. The popular Rockshox Pike RCT3 fork also has a comparable degree of external adjustability to it's nearest rival, however the specific LSC adjustement only has an effect when the compression dial is set fully open.
So why would I adjust my low-speed compression?
Whilst it would be awesome if our Monday to Fridays consisted of downward trails for days, in reality they don't, and we need to climb, and pedal (and work dammit)!  So with consideration firstly to pedaling efficiency, the more LSC that you turn on, the more likely the fork or shock will feel a little more stable under pedaling forces, and the pedal 'bob' will be reduced. With less LSC turned on, you will more than likely experience more pedalling induced bob, and in forks, you may experience an increase in front end 'brake-dive' during heavy braking. With many of our managed trail networks featuring flowing berms, lots of pedaling and sometimes a limited number of heavy HSC hits, it can often be more efficient for the average rider to ride those trails in the middle setting that is set to your desired feel. Secondly, as you may adjust your air pressures for particular events, riding locations, or following a modification of the air volume inside, you may then also find the need to make small adjustments to the LSC adjuster to fine tune your ride's performance accordingly.
How does the compression damper's lockout function work? 
This is the most common form of compression adjustment as it quite simply allows us to fully control the fork or shocks range of movement, from fully 'open', to fully 'closed' and often many settings in between. When you turn that lever or dial to the 'lockout' position, you are basically mechanically closing the compression damper and piston assembly inside,  stopping oil from being able to flow through it, and thus stopping the fork or shock from being able to compress. Whilst there are many varying methods in which the suspension guru's have designed the lockout function, they will almost always have a form of 'blow-through' that allows oil to bypass that closed circuit in the event of a high speed impact or for those times when you forget to unlock before that gnarly drop.
FIT4 Performance SeriesFIT4 Factory Series
3) Rebound: This is the adjustment of how fast or slow a fork or shock is able to extend back to it's neutral position following an impact. (Note, the rebound adjuster is almost always RED). If your rebound adjustment is fully open or turned counter clockwise to the limit, it will be in it's fastest setting, which for most forks or shocks will give the rider a 'pogo-stick' kind of feel, often resulting in the trail feeling rougher than it actually is! This can lead to several adverse affects such as 'bucking' your front or back wheel sky high when tackling higher speed obstacles including the up-ramp off jumps and the aftermath of heavy landings. On the flip side, if you wind your rebound adjusters all the way inwards (clockwise), you will then be in the slowest setting which for most forks or shocks will translate a severely harsh trail feel to the rider. This is because you are not allowing the fork or shock enough time following an impact to react and return to it's neutral position before it takes the next impact, and in effect it begins to 'pack-down' into it's travel. A 140mm travel fork can quickly feel like a 80mm travel fork with rebound settings too slow.
Here's some common questions relating to rebound:
Ok, so too fast is bad, and too slow is bad, so where do I set my rebound?
This is a hard one to answer directly as every rider, bike and terrain combination will have a different setting, however we will confidently say that the majority of us will be satisfied with our rebound being set at a couple of turns on the faster side of the mid point of adjustment. Ie, if your rebound dial in the fork or shock has 5 full turns (or clicks) of adjustment from fully out to fully wound in, you will more than likely be happy with 1-2 full turns (or clicks) inwards of that rebound knob from fully unwound. That's a good starting point, then you can make small changes as you see fit with consideration to the differences explained above between 'fast' and 'slow' rebound, and that with varying weighted riders the rebound settings will differ.
Can you modify a fork or shocks's rebound adjustment range internally?
Yes, the rebound settings are also 'tuneable' in most forks and shocks, and will normally be done so by reconfiguring the rebound shim stack within the fork or shocks rebound damper circuit. For example: If you are happy with your air spring pressures used, but are finding the rebound adjustment at its fully un-wound or 'fastest' position is till too slow you may feel the fork or shock rides super harsh and lacks compliance. This would be a good reason to 'tune' the rebound circuit to achieve a controlled but faster flow of oil back through the rebound piston and shim stack resulting in an overall faster rebound rate. Following an internal 'tune' or modification, you would then be able to make the fine adjustments to your new preferred settings using the external rebound knob.
My rebound adjuster doesn't seem to do anything?
If the fork or shock's rebound adjustment is not apparent at all throughout it's full range of the adjuster, there's a good chance that the fork or shock's damper has lost oil, and is in need of some loving and a good service. Loss of any rebound control is often a dead giveaway for a 'blown' or severely airated and cavitated damper, as when oil has leaked or blown out from the damper assembly, it allows little to no path of resistance for the rebound piston/damper to extend, and thus it usually extends violently with often a nasty 'top-out' feeling.
Hope that helps you identify some of your fork or shocks adjusters and how they work. Of course if you have any queries, you can contact us 24/7 via email, or call us during business hours on 07 3157 4480