Rod B.
Well-known member
This is Part Two in a three part series on suspension, tuning, hacks and tips. I've always enjoyed the people on the Orbea forum and I've met a lot of good people and many new ride partners through this forum. If you're looking for new ride partners, I encourage you to reach out to other members on this forum who live near you and your ride area. It's all good...
You can reference Part One in the series here:
www.emtbforums.com
You can reference Part Three in the series here:
www.emtbforums.com
You will often hear YouTubers and other bike reviewers describe a bike's suspension as "Linear" or "Progressive." These two terms are used to describe how a suspension component's air spring reacts to compressive forces.
When we describe an air spring rate, we are referring to the force required to compress the fork or shock. In a perfect world, when a fork or shock compresses, the force required to compress the component is the same from initial compression to full bottom out compression. This rate of compression is what's known as "Linear" i.e. straight compression through the component's stroke. Most mountain bike suspension components will have what's known as a Progressive air spring rate of compression. A "Progressive" rate means that the force required to compress the suspension component increases in a curve at "Mid" and "End" stroke.
The air spring ramp up rate on your mountain bike suspension can be custom tuned by you to make your suspension more Linear or Progressive. Why would you want to change your air spring's rate of compression? In some situations a rider may prefer to have their fork or shock ramp up more quickly at mid and end stroke. As an example, if a rider is hitting big jumps and compressing his or her suspension to the point of bottoming out, then the rider would benefit from a firmer mid and end stroke to avoid suspension bottom out. On the other hand, if a rider predominantly rides smooth or less aggressive trails, then that rider would benefit from a more linear rate of air spring compression as this would offer a more plush, less firm ride at mid and end stroke. Every rider should tune the air spring ramp up rate on their suspension to what suits the area they ride and riding style.
To tune the air spring ramp up rate of your Fork and or Shock, Fox utilizes air volume spacers. Rockshox uses the term "Tokens." The purpose of the air volume spacers is to "Decrease" the interior volume in the air chamber on a fork or shock. Air volume spacers/tokens can be removed to increase interior volume in a fork or shock's air chamber. By adjusting the air chamber volume you can fine tune the air spring compression rate on your suspension.
Adding an air volume spacer, will affect the air spring "Ramp Up" rate on your suspension. Seen below in blue is a Linear rate of air spring progression. You can "Decrease" the air chamber volume in a suspension component by adding an air volume spacer to the air chamber. When you decrease air chamber volume, this causes the air in the chamber to compress quicker and you thus alter the air spring's ramp up rate at mid to end stroke. The air spring rate becomes progressive as seen in green. Note the ramp up rate of the green graph line at mid and end stroke. You can fine tune the ramp up rate by the amount of air volume spacers which you add or you "Remove" from the air chamber.
There are various reasons why you would want to add air volume spaces. Here are some typical reasons:
a. You find that after setting the correct sag on your fork or shock, you are bottoming out. You'll know this is occurring because you remembered to set the sag "O" ring before your ride. At the end of your ride you find that the sag "O" ring has been pushed off the back of the rear shock, or the "O" has been pushed tightly up against the upper fork crown.
Your first thought is to just add more air to the air chamber. Air is good....but after doing so, you find that you are now riding overly high and no longer achieving correct sag, i.e. 20%-30% of travel. The increased air pressure which you added has now caused your bike to loose some small bump compliance and it's riding very harsh. Instead of adding more air, try add a single air volume spacer and again set correct sag. If you bike is no longer bottoming out, you're good to go. if you find you are still bottoming out after setting correct sag, then add another air volume spacer and repeat the process.
Note: Ideally, you want the sag O ring to be approximately 1/4 inch or about 6mm from the end of the rear shock's shaft after taking a few hard hits. You want the sag O ring to be about 3/4 inch or approximately 19mm from the fork crown after taking a few hard hits. It's important to note that all Forks and shocks have an internal rubber bottom out bumper. On Fox shocks this bumper comes in the form of a thick O ring located internally on the main piston shaft. On Fox forks, the bumper comes in the form of a rubber cushion located internally at the base of the lower leg assembly. Ideally, you don't want the Shock or fork stanchion to go smashing into the bumper. This is exceptionally hard on the linkage and frame, and also can harm the shock or fork.
b. In another example, suppose you've set perfect sag and your bike isn't bottoming out while riding your favorite local blue trail. However, your jackass of a friend talks you into doing a 15 foot gap jump. He tells you that you're "Money", he says he hit it last week, and you've "Got This, Yea Boy!" You hit the gap and stick the landing, however your bike bottoms out and you crash like a good thing and you also screw up your new helmet. As a side note, your jackass of a friend owes you a beer. To prevent bottoming out next time, you add an air volume spacer/token. This causes your air spring rate to ramp up firmer towards the end of mid and end stroke and your bike no longer bottoms out on big hits. The trade off is your bike may ride a bit overly firm at mid to end stroke.
c. In another example, you buy a new Fox 36 fork from your local bike shop. The fork has 160mm of travel. Fox 36 forks with 160mm of travel come stock from the Fox factory with two air volume spacers added. You find after installing the fork your bike feels overly stiff/harsh at mid stroke and not that plush when you encounter small rock gardens. You check air pressure, sag, compression and rebound settings. Your bike still rides stiff at mid stroke. You remove one or both of the air volume spacers. You reset you sag and the bike now feels good at mid to end stroke.
Instead of adding excessive higher air pressures to a fork or shock, try adding an air volume spacer instead. Air volume spacers remove volume i.e. space from the air chamber. This allows you to run a lower positive air pressure and at the same time, avoid bottoming out. There's always a catch....Adding an air volume spacer will cause your air spring to ramp up quicker at mid to end stroke. This means that when the fork or shock reaches mid stroke in the travel, the air in the positive air chamber is compressing that much quicker because the air volume in the air chamber has been decreased by the air volume spacer which you installed. The force now required to compress the component increases at mid to end stroke.
Air volume spacers are good, but they should not be blindly installed just because your buddy said he heard from a friend who has a friend, that two volume spacers on a ZEB or Fox is ideal. Whether or not you install an air volume spacer depends on two things, 1. Are you reaching proper sag and still bottoming out while riding normal trail? Then add an air volume spacer 2. Are you doing highly compressive stunts that require your air spring to quickly ramp/firm up in order to overcome the force of a big hit and prevent your bike from bottoming out? Then add an air volume spacer.
There's no hard and fast rule for installing an air volume spacer. You just need to know why you are doing it and what you are attempting to achieve.
As for me personally, I ride very rocky and aggressive trails, but I don't jump. I run zero air volume spacers on my 170mm ZEB. My low speed compression is set wide open and my high speed compression is set four clicks from wide open. I run zero spacers on my Fox X2, I run my low speed compression wide open and my high speed compression two clicks from wide open. I love boosting my Levo off trail side kickers, I like moderate drops, but I'm not a big jump kind of guy. No huge compressive forces created and thus no air volume spacers needed.
Fox 36 Air volume Spacer. The "10cc" refers to the amount of spatial volume lost in the positive air chamber when installed.
Fox Float DPS air volume spacers. The color signifies the amount of volume lost in the air chamber when installed. A volume chart is provided with the air volume spacer kit that identifies the size of the spacer. Instead of using CC's as a means of measurement, Fox utilizes thickness for shock air volume spacers, i.e. 0.2 inches, 0.4 inches, etc.
Fox Float X Air volume spacers (Note the difference in color as compared to the DPS spacers.)
Fox X2 Air Volume Spacers
ZEB tokens. Rockshox uses the term "Tokens" when referring to fork air volume spacers
Damper Tuning:
Picture a cowboy movie. You see a herd of cattle and a few cowboys riding herd on the cattle. Suddenly the cows stampede and the cowboys ride back and forth regaining control over the cattle. Your damper is the cowboy and the cows are the air spring. The damper and the air spring are in a constant struggle with each other. The air spring wants to "Compress", but the damper wants to slow it down. The air spring wants to "Rebound", but the damper wants to slow the rebound. The damper essentially rides herd on the air chamber......get it? Without the damper, the air spring would behave like a deranged pogo stick, you'd be bounced off your bike on a hard hit. The damper has a tough job. If the air spring is not adjusted correctly, the damper will have difficulty maintaining control during the compression and rebound cycles.
The damper uses oil to control the air spring's rate of compression and rebound. This is done through a series of shims, valving, and ported pistons Much like air, oil is vital to a shock or fork's function. Do not confuse the oil that is added to a shock or fork during a wiper seal service. We're talking about oil located seep inside the damper assembly.
I've always felt that one of the issues with the Rise M20 and other lower cost Rise models, is the Fox Float DPS rear shock that comes stock on the bike. The Fox Float DPS is a very good shock, however it's best suited for light duty trail or cross country riding. When you couple a heavy eBike and an aggressive rider, the Float DPS has it's hands full trying to regulate compression and rebound.
When looking at Float DPS you will find the shock has no piggyback reservoir which can store extra damper oil. Try touching your rear shock after a hammering downhill run. If your bike has a Fox Float DPS, you'll find the shock is very hot to the touch. Due to the lack of a piggyback reservoir, the Fox Float DPS has a limited amount of damper oil. While riding, the oil is in a constant state of motion as it flows back and forth through piston ports, past valving and shims. The harder you push the shock, the faster the oil flows and friction soon develops. Friction will cause the oil in the damper to get hot. Oil when exposed to high heat tends to loose viscosity, i.e. oil thickness. Reduced viscosity impacts the effectiveness of the damper to control compression and rebound. Don't get me wrong, if you are riding mellow trails, it's not an issue, the shock is brilliant. However, if you routinely take your Rise/Wild down chunky black trails, or you're a heavy rider and like to spank the bike, you may want to consider upgrading to a rear shock with a piggyback reservoir.
Fox Float, Performance Rear Shock. Note the lack of a piggyback reservoir.
Fox Float X Factory with it's piggyback reservoir
We discussed previously that "Air Shafts" can be replaced on a Fox fork to increase or decrease travel. Damper's on Fox forks can also be replaced. As an example, say you bought a budget generic Fox fork and wish to change the FIT GRIP damper to a GRIP 2 . This is an acceptable modification and easily done. However, you must purchase the correct part for your fork. Note that dampers on a shock can be modified also, but modifications to the valving or valve assembly requires special tools and knowledge.
To determine which parts will fit your shock or fork, you will first need to run the fork or shocks component serial code on Fox's "Tech Help" page. After identifying your fork or shock's year of manufacture and model, you can find a parts list and diagrams detailing the correct parts and part numbers. From there you can go shopping online to purchase the parts.
Here's an example of a 2022 Fox Float DPS parts page on Fox's website:
When Fox develops a shock or fork, they attempt to tune the fork or shock so that the damper works for a wide bell curve of riders. The bell curve is based on rider weight and how Fox wishes the generic shock or fork to perform on a wide range of bicycles. If you are a 95lb. rider, you may have difficulty setting the shock up and reaching correct sag. If you are a heavier rider, i.e. 260lbs., you may have problems setting the shock or fork up. Ideally, you want to be in the middle of the bell curve to get the best results from a generic fork or shock.
Manufactures often times will have Fox create a custom damper tune for a particular bike model. Manufacturers spend a lot of money on bicycle design and handling. They want the bicycle to perform to the best of it's abilities. Manufacturers will often ask Fox to perform a Custom Tune which the manufacturer specifies in order to enhance a bike's handling. You will often see a sticker on the side of a bike's shock proclaiming "Custom Tune."
Suppose you are at the outer fringe of the bell curve and you're having issues with setting the generic shock or fork up? Fortunately, there are numerous suspension specialists available who can custom tune a shock or fork's damper to work specifically for your weight and riding style. The suspension expert will typically meet with you in person or via phone. The tuning specialist will discuss with you in regards to how you ride and what specifically you are trying to achieve. As an example I met with a tuning specialist and explained that my ankle was toast and I needed a plush damper, but with a more progressive spring rate for my trips to Hurricane Utah. Once the expert has an idea of what you are trying to accomplish, he'll discuss shim stacks and tuning. When you both agree on a course of action the tuning work is performed. This usually takes on a few days if your tuner is local and works out of a bike shop. The results of a well tuned shock/damper are incredible.
So, how does a damper work? To better understand this, let's first look at a drawing of a basic automotive shock absorber which is depicted below. The drawing shows rebound and compression cycles on the shock.
On the rebound cycle, i.e. the shock is expanding. The red oil flows through a port in the piston and into the green chamber. The rate of rebound is controlled by the diameter of the hole/port in the piston. As the oil attempts to flow through the port, the size of the port only allows a set amount of oil to transfer through the port. No more, no less, thus the rate of rebound is firmly controlled.
On the compression cycle, the Red oil flows back through the piston port and into the orange chamber. The rate of compression is controlled by the size of the port in the piston. The size of the port only allows a set amount of oil to transfer through the port and thus the rate of compression is firmly controlled.
The damper on your shock or fork behaves in a similar manner, however the process is much more complicated. Here's a picture of a Rockshox fork damper. Imagine working on this beauty. Oil is forced through a series of valves and piston ports to control the rate of compression and Rebound. Keep in mind that the internals on a fork or shock damper is much more complicated the the basic drawing depicted.
Pictured are several cut away examples of Rockshox damper assemblies
A damper on a mountain bike utilizes similar piston and ports like the automotive shock, however the damper also utilizes shim stacks and valving. A series of shims with various thicknesses are placed on a valve port or valve assembly upon which the oil flows through. The shims act like a gate keeper to regulate the flow of oil. When the oil pressure builds up, the shims will bend and open, thus releasing the oil and allowing it to flow. A custom tune utilizes shims of various thicknesses to control the flow of oil and thus regulate how a shock or fork compresses or rebounds. Shims can wear out with time and fluctuation. When this occurs , you'll usually find your rebound knob adjustment or possibly your compression knob adjustment no longer works. Fortunately, most dampers can be repaired or the damper replaced.
For this next exemplar, I am going to use a Fox Float X shock to show a shim stack series for the main piston. Fox offers numerous shim stacks for all internal areas of the Float X. The shims also known as valving, come in various thicknesses. It's the thickness of a shim/valve which determines the rate of oil flow.
Depicted in the photo below is a Fox Float DPS shim stack/valve for the lock out piston.
This will conclude Part Two in the suspension series. Refer to Part Three for the Fox Float X Performance hack and other useful tips to improve the performance of your suspension.
Be safe,
Rod
You can reference Part One in the series here:
Technical Article, Part # 1: Suspension, The Ups, The Downs, The Hacks
Hello, It's been a while since I've posted anything for the Orbea Forum. This will be a three part series on basic suspension and simple to perform suspension hacks that you might find interesting and helpful. If you have a "Simple" to perform suspension hack, post it to this thread so others...
www.emtbforums.com
You can reference Part Three in the series here:
Technical Article, Part # 3: Suspension, The Ups, The Downs, The Hacks
Greetings, This will be the third installment in a three part series on suspension. This third installment will cover hacking a Fox Float X Performance shock and other small performance tips that you can do to improve your suspension. You can find read the first two installments via the...
www.emtbforums.com
You will often hear YouTubers and other bike reviewers describe a bike's suspension as "Linear" or "Progressive." These two terms are used to describe how a suspension component's air spring reacts to compressive forces.
When we describe an air spring rate, we are referring to the force required to compress the fork or shock. In a perfect world, when a fork or shock compresses, the force required to compress the component is the same from initial compression to full bottom out compression. This rate of compression is what's known as "Linear" i.e. straight compression through the component's stroke. Most mountain bike suspension components will have what's known as a Progressive air spring rate of compression. A "Progressive" rate means that the force required to compress the suspension component increases in a curve at "Mid" and "End" stroke.
The air spring ramp up rate on your mountain bike suspension can be custom tuned by you to make your suspension more Linear or Progressive. Why would you want to change your air spring's rate of compression? In some situations a rider may prefer to have their fork or shock ramp up more quickly at mid and end stroke. As an example, if a rider is hitting big jumps and compressing his or her suspension to the point of bottoming out, then the rider would benefit from a firmer mid and end stroke to avoid suspension bottom out. On the other hand, if a rider predominantly rides smooth or less aggressive trails, then that rider would benefit from a more linear rate of air spring compression as this would offer a more plush, less firm ride at mid and end stroke. Every rider should tune the air spring ramp up rate on their suspension to what suits the area they ride and riding style.
To tune the air spring ramp up rate of your Fork and or Shock, Fox utilizes air volume spacers. Rockshox uses the term "Tokens." The purpose of the air volume spacers is to "Decrease" the interior volume in the air chamber on a fork or shock. Air volume spacers/tokens can be removed to increase interior volume in a fork or shock's air chamber. By adjusting the air chamber volume you can fine tune the air spring compression rate on your suspension.
Adding an air volume spacer, will affect the air spring "Ramp Up" rate on your suspension. Seen below in blue is a Linear rate of air spring progression. You can "Decrease" the air chamber volume in a suspension component by adding an air volume spacer to the air chamber. When you decrease air chamber volume, this causes the air in the chamber to compress quicker and you thus alter the air spring's ramp up rate at mid to end stroke. The air spring rate becomes progressive as seen in green. Note the ramp up rate of the green graph line at mid and end stroke. You can fine tune the ramp up rate by the amount of air volume spacers which you add or you "Remove" from the air chamber.
There are various reasons why you would want to add air volume spaces. Here are some typical reasons:
a. You find that after setting the correct sag on your fork or shock, you are bottoming out. You'll know this is occurring because you remembered to set the sag "O" ring before your ride. At the end of your ride you find that the sag "O" ring has been pushed off the back of the rear shock, or the "O" has been pushed tightly up against the upper fork crown.
Your first thought is to just add more air to the air chamber. Air is good....but after doing so, you find that you are now riding overly high and no longer achieving correct sag, i.e. 20%-30% of travel. The increased air pressure which you added has now caused your bike to loose some small bump compliance and it's riding very harsh. Instead of adding more air, try add a single air volume spacer and again set correct sag. If you bike is no longer bottoming out, you're good to go. if you find you are still bottoming out after setting correct sag, then add another air volume spacer and repeat the process.
Note: Ideally, you want the sag O ring to be approximately 1/4 inch or about 6mm from the end of the rear shock's shaft after taking a few hard hits. You want the sag O ring to be about 3/4 inch or approximately 19mm from the fork crown after taking a few hard hits. It's important to note that all Forks and shocks have an internal rubber bottom out bumper. On Fox shocks this bumper comes in the form of a thick O ring located internally on the main piston shaft. On Fox forks, the bumper comes in the form of a rubber cushion located internally at the base of the lower leg assembly. Ideally, you don't want the Shock or fork stanchion to go smashing into the bumper. This is exceptionally hard on the linkage and frame, and also can harm the shock or fork.
b. In another example, suppose you've set perfect sag and your bike isn't bottoming out while riding your favorite local blue trail. However, your jackass of a friend talks you into doing a 15 foot gap jump. He tells you that you're "Money", he says he hit it last week, and you've "Got This, Yea Boy!" You hit the gap and stick the landing, however your bike bottoms out and you crash like a good thing and you also screw up your new helmet. As a side note, your jackass of a friend owes you a beer. To prevent bottoming out next time, you add an air volume spacer/token. This causes your air spring rate to ramp up firmer towards the end of mid and end stroke and your bike no longer bottoms out on big hits. The trade off is your bike may ride a bit overly firm at mid to end stroke.
c. In another example, you buy a new Fox 36 fork from your local bike shop. The fork has 160mm of travel. Fox 36 forks with 160mm of travel come stock from the Fox factory with two air volume spacers added. You find after installing the fork your bike feels overly stiff/harsh at mid stroke and not that plush when you encounter small rock gardens. You check air pressure, sag, compression and rebound settings. Your bike still rides stiff at mid stroke. You remove one or both of the air volume spacers. You reset you sag and the bike now feels good at mid to end stroke.
Instead of adding excessive higher air pressures to a fork or shock, try adding an air volume spacer instead. Air volume spacers remove volume i.e. space from the air chamber. This allows you to run a lower positive air pressure and at the same time, avoid bottoming out. There's always a catch....Adding an air volume spacer will cause your air spring to ramp up quicker at mid to end stroke. This means that when the fork or shock reaches mid stroke in the travel, the air in the positive air chamber is compressing that much quicker because the air volume in the air chamber has been decreased by the air volume spacer which you installed. The force now required to compress the component increases at mid to end stroke.
Air volume spacers are good, but they should not be blindly installed just because your buddy said he heard from a friend who has a friend, that two volume spacers on a ZEB or Fox is ideal. Whether or not you install an air volume spacer depends on two things, 1. Are you reaching proper sag and still bottoming out while riding normal trail? Then add an air volume spacer 2. Are you doing highly compressive stunts that require your air spring to quickly ramp/firm up in order to overcome the force of a big hit and prevent your bike from bottoming out? Then add an air volume spacer.
There's no hard and fast rule for installing an air volume spacer. You just need to know why you are doing it and what you are attempting to achieve.
As for me personally, I ride very rocky and aggressive trails, but I don't jump. I run zero air volume spacers on my 170mm ZEB. My low speed compression is set wide open and my high speed compression is set four clicks from wide open. I run zero spacers on my Fox X2, I run my low speed compression wide open and my high speed compression two clicks from wide open. I love boosting my Levo off trail side kickers, I like moderate drops, but I'm not a big jump kind of guy. No huge compressive forces created and thus no air volume spacers needed.
Fox 36 Air volume Spacer. The "10cc" refers to the amount of spatial volume lost in the positive air chamber when installed.
Fox Float DPS air volume spacers. The color signifies the amount of volume lost in the air chamber when installed. A volume chart is provided with the air volume spacer kit that identifies the size of the spacer. Instead of using CC's as a means of measurement, Fox utilizes thickness for shock air volume spacers, i.e. 0.2 inches, 0.4 inches, etc.
Fox Float X Air volume spacers (Note the difference in color as compared to the DPS spacers.)
Fox X2 Air Volume Spacers
ZEB tokens. Rockshox uses the term "Tokens" when referring to fork air volume spacers
Damper Tuning:
Picture a cowboy movie. You see a herd of cattle and a few cowboys riding herd on the cattle. Suddenly the cows stampede and the cowboys ride back and forth regaining control over the cattle. Your damper is the cowboy and the cows are the air spring. The damper and the air spring are in a constant struggle with each other. The air spring wants to "Compress", but the damper wants to slow it down. The air spring wants to "Rebound", but the damper wants to slow the rebound. The damper essentially rides herd on the air chamber......get it? Without the damper, the air spring would behave like a deranged pogo stick, you'd be bounced off your bike on a hard hit. The damper has a tough job. If the air spring is not adjusted correctly, the damper will have difficulty maintaining control during the compression and rebound cycles.
The damper uses oil to control the air spring's rate of compression and rebound. This is done through a series of shims, valving, and ported pistons Much like air, oil is vital to a shock or fork's function. Do not confuse the oil that is added to a shock or fork during a wiper seal service. We're talking about oil located seep inside the damper assembly.
I've always felt that one of the issues with the Rise M20 and other lower cost Rise models, is the Fox Float DPS rear shock that comes stock on the bike. The Fox Float DPS is a very good shock, however it's best suited for light duty trail or cross country riding. When you couple a heavy eBike and an aggressive rider, the Float DPS has it's hands full trying to regulate compression and rebound.
When looking at Float DPS you will find the shock has no piggyback reservoir which can store extra damper oil. Try touching your rear shock after a hammering downhill run. If your bike has a Fox Float DPS, you'll find the shock is very hot to the touch. Due to the lack of a piggyback reservoir, the Fox Float DPS has a limited amount of damper oil. While riding, the oil is in a constant state of motion as it flows back and forth through piston ports, past valving and shims. The harder you push the shock, the faster the oil flows and friction soon develops. Friction will cause the oil in the damper to get hot. Oil when exposed to high heat tends to loose viscosity, i.e. oil thickness. Reduced viscosity impacts the effectiveness of the damper to control compression and rebound. Don't get me wrong, if you are riding mellow trails, it's not an issue, the shock is brilliant. However, if you routinely take your Rise/Wild down chunky black trails, or you're a heavy rider and like to spank the bike, you may want to consider upgrading to a rear shock with a piggyback reservoir.
Fox Float, Performance Rear Shock. Note the lack of a piggyback reservoir.
Fox Float X Factory with it's piggyback reservoir
We discussed previously that "Air Shafts" can be replaced on a Fox fork to increase or decrease travel. Damper's on Fox forks can also be replaced. As an example, say you bought a budget generic Fox fork and wish to change the FIT GRIP damper to a GRIP 2 . This is an acceptable modification and easily done. However, you must purchase the correct part for your fork. Note that dampers on a shock can be modified also, but modifications to the valving or valve assembly requires special tools and knowledge.
To determine which parts will fit your shock or fork, you will first need to run the fork or shocks component serial code on Fox's "Tech Help" page. After identifying your fork or shock's year of manufacture and model, you can find a parts list and diagrams detailing the correct parts and part numbers. From there you can go shopping online to purchase the parts.
Here's an example of a 2022 Fox Float DPS parts page on Fox's website:
When Fox develops a shock or fork, they attempt to tune the fork or shock so that the damper works for a wide bell curve of riders. The bell curve is based on rider weight and how Fox wishes the generic shock or fork to perform on a wide range of bicycles. If you are a 95lb. rider, you may have difficulty setting the shock up and reaching correct sag. If you are a heavier rider, i.e. 260lbs., you may have problems setting the shock or fork up. Ideally, you want to be in the middle of the bell curve to get the best results from a generic fork or shock.
Manufactures often times will have Fox create a custom damper tune for a particular bike model. Manufacturers spend a lot of money on bicycle design and handling. They want the bicycle to perform to the best of it's abilities. Manufacturers will often ask Fox to perform a Custom Tune which the manufacturer specifies in order to enhance a bike's handling. You will often see a sticker on the side of a bike's shock proclaiming "Custom Tune."
Suppose you are at the outer fringe of the bell curve and you're having issues with setting the generic shock or fork up? Fortunately, there are numerous suspension specialists available who can custom tune a shock or fork's damper to work specifically for your weight and riding style. The suspension expert will typically meet with you in person or via phone. The tuning specialist will discuss with you in regards to how you ride and what specifically you are trying to achieve. As an example I met with a tuning specialist and explained that my ankle was toast and I needed a plush damper, but with a more progressive spring rate for my trips to Hurricane Utah. Once the expert has an idea of what you are trying to accomplish, he'll discuss shim stacks and tuning. When you both agree on a course of action the tuning work is performed. This usually takes on a few days if your tuner is local and works out of a bike shop. The results of a well tuned shock/damper are incredible.
So, how does a damper work? To better understand this, let's first look at a drawing of a basic automotive shock absorber which is depicted below. The drawing shows rebound and compression cycles on the shock.
On the rebound cycle, i.e. the shock is expanding. The red oil flows through a port in the piston and into the green chamber. The rate of rebound is controlled by the diameter of the hole/port in the piston. As the oil attempts to flow through the port, the size of the port only allows a set amount of oil to transfer through the port. No more, no less, thus the rate of rebound is firmly controlled.
On the compression cycle, the Red oil flows back through the piston port and into the orange chamber. The rate of compression is controlled by the size of the port in the piston. The size of the port only allows a set amount of oil to transfer through the port and thus the rate of compression is firmly controlled.
The damper on your shock or fork behaves in a similar manner, however the process is much more complicated. Here's a picture of a Rockshox fork damper. Imagine working on this beauty. Oil is forced through a series of valves and piston ports to control the rate of compression and Rebound. Keep in mind that the internals on a fork or shock damper is much more complicated the the basic drawing depicted.
Pictured are several cut away examples of Rockshox damper assemblies
A damper on a mountain bike utilizes similar piston and ports like the automotive shock, however the damper also utilizes shim stacks and valving. A series of shims with various thicknesses are placed on a valve port or valve assembly upon which the oil flows through. The shims act like a gate keeper to regulate the flow of oil. When the oil pressure builds up, the shims will bend and open, thus releasing the oil and allowing it to flow. A custom tune utilizes shims of various thicknesses to control the flow of oil and thus regulate how a shock or fork compresses or rebounds. Shims can wear out with time and fluctuation. When this occurs , you'll usually find your rebound knob adjustment or possibly your compression knob adjustment no longer works. Fortunately, most dampers can be repaired or the damper replaced.
For this next exemplar, I am going to use a Fox Float X shock to show a shim stack series for the main piston. Fox offers numerous shim stacks for all internal areas of the Float X. The shims also known as valving, come in various thicknesses. It's the thickness of a shim/valve which determines the rate of oil flow.
Depicted in the photo below is a Fox Float DPS shim stack/valve for the lock out piston.
This will conclude Part Two in the suspension series. Refer to Part Three for the Fox Float X Performance hack and other useful tips to improve the performance of your suspension.
Be safe,
Rod
Last edited:
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