Demystifying MTB Suspension: Adjusters
What's the difference between High-Speed Compression and Low-Speed Compression? Many suspension components have both High-Speed Compression (HSC) and Low-Speed Compression (LSC) adjusters, as well as High-Speed Rebound (HSR) and Low-Speed Rebound (LSR). Read on to learn more about how these adjusters work and effect your ride.
The balance of your suspension is crucial to the performance of how well your bike handles. One way to address balance is with air pressure and sag, which we touched on in other blog posts, but you can fine-tune the characteristics of suspension with adjusters. Most of the time, adjusters are blue and red knobs on the top and bottom of the fork and shock. The more expensive the suspension, the more adjusters are typically at your disposal. Let’s look at the two types of damping circuits, what adjusters do and how to use them. Click here for sag blog post
How Low-Speed Adjusters Work:
If your mtb fork or shock only has one adjuster for compression and one for rebound, these are low-speed adjusters. If you have two adjusters for compression and rebound, then the adjuster that is smaller will be low speed. Inside the damper, the low-speed adjuster is typically a tapered needle that determines the rate of oil flow through the low-speed circuit. Picture a screw being screwed into a hole. If the needle(screw) is further into the pathway, it will restrict oil flow. Restricting oil flow makes compression stiffer and rebound slower. If the needle is further away from the oil pathway (more oil is allowed to flow), less resistance means faster compression and faster rebound. Places on the trail that are typically low speed adjustments would be entering and exiting corners, going off the face of a jump, and pumping over rollers (think flow trail). Mountain bike suspension adjustments are dictated by the shaft speed. During these parts of the trail your fork and shock are cycling slow even though your wheels are rotating fast. You can really affect the balance of the bike by adjusting your low-speed compression and rebound adjusters.
Once the low-speed circuit is overcome with too much oil flow, the oil must bleed off somewhere, and that is where the high-speed circuit takes over.
How High-Speed Adjusters Work:
If your mountain bike suspension has both low and high-speed compression and rebound adjusters, high-speed will be the larger knob for both circuits. There are a few different types of high-speed compression designs but let's talk about ones that are controlled with shims. In our opinion this works and feel the best. When the oil flows through the high-speed piston, the oil bends or deflects the shims. The more resistant the shims are to bending, the stiffer the compression will be and the slower the rebound becomes (and vice versa). When we custom tune we can manipulate damping and how the oil is controlled by the thickness and diameter of the shims and their orientation. Styles of tuning are called 2 stage or single stage damping. Typically, larger quantities of thinner shims feel better than fewer thicker shims. Thicker shims will also deform faster than thin shims. In most dampers, the high-speed compression adjuster puts preload on shims which helps restrict the flow of oil giving resistance to the oil and making your suspension stiffer or slower for those larger and fast hits. High speed adjustments occur when landing off a drop, off a jump, roots, and square edge rocks/rock gardens. If you are bottoming out or getting too much travel, then increasing resistance (adding compression) will help. Generally, the faster you ride you need faster rebound. You need your rebound settings to extend the fork and shock fast and controlled so they are ready for the next compression hit. This would be backing off the high-speed rebound or less damping.
Determining What Adjuster to Adjust:
What adjuster should you be adjusting? It’s important to remember that what you adjust is dependent on how fast the fork or shock is cycling, not wheel speed. Your wheels could be moving 80 MPH, but the trail is smooth and flowing; any adjustment made in this situation should be low speed. Landing off a jump or drop or smashing through a rock garden with square edge hits, should be a high-speed adjustment. Get the idea? Rebound speeds are arguably more important than compression because the idea is to have your fork or shock return to the sag point, or about full extension, before the next hit. This allows the suspension to absorb the bumps, keeping the bike feeling plush and compliant. The more extended your suspension is when it hits the obstacle, the less force it takes to compress the fork or shock. If you are constantly too deep in the travel, this is called “packing”, meaning the fork or shock cannot extend, so they pack up. If this happens, your suspension is now deflecting, causing the bike to feel harsh and non-compliant. A lot of people confuse this with compression being too stiff and then make an adjustment that makes compression softer, which makes the situation worse. In a lot of cases, if you make the suspension stiffer and faster, the bike will track better and be more comfortable. It’s very counterintuitive!
For example, picture yourself entering a corner and you are on the brakes. Your fork dives and your shock extends. What could you adjust to level the bike out? This usually would be a low-speed adjustment, and you could stiffen the fork’s Low Speed compression to keep the front end higher. Or slow the shock low speed rebound to keep the shock lower in its travel. Or both. There isn’t a wrong adjustment. It’s recommended to only make one adjustment at a time, so you don’t get confused, and you can learn what each adjustment does.
How Low-Speed Adjustments Effect High-Speed Adjustments:
In most designs there is a direct correlation between the low and high-speed circuits, despite what the marketing may say. As explained above, most high-speed circuits are activated once the flow of oil has become too great for the low-speed circuits. If you completely close off your low-speed adjusters, the brunt of the work will be passed on to the high-speed circuit. Think of your Low-Speed adjusters as the main adjustment for most suspension inputs, then dial in your high-speed for landings and chunky sections.
Summary:
In summary, don’t be scared to use the adjusters to see what they do. You should figure out where you are in the adjuster’s range so you can go back to that spot if you get lost. F-Ftuned.com is a great website where you can log your bike settings and the adjustments, and it’s all free! It is extremely important to remember that you do not adjust for one part of the trail but think about how the adjustments you make will affect the overall big picture. Some people like a set-it-and-forget-it method; others like to tinker with settings depending on the trail. There is so much more to all of this, but hopefully this is the start of making the adjustments you have been hesitating to make!
Still have questions? Don’t hesitate to contact us for more information! We would love to help you get your suspension feeling and performing its best.
