TwentyThreeMX
PR Founding Father
Saw this posted from someone over on vital. have been hearing things here and there from people, opinions good and bad. been trying to dig into it because im really considering a new honda..or kaw, both with the air forks. or the suzuki.. the below makes me want the yellow bike!!
in short, if they leak, you are done. no wiping off your leaky oil and riding the rest of the day. 2. it will pretty much just collapse. also it actually sucks the front end down. imagine that happening on the face of a jump. good things? tuneable..
interesting view on the costs of it, didnt really think about it like that. makes sense to me.
whats everyone else think?
-------------
Here are some things that may help to better understand the new 2013 PSF forks. This applies to both the 2013 CRF450R and the 2013 KX450F.
What is the PSF?
It is a fork that is more of a pneumatic or air fork than last year, but it is not a “spring-less” fork. Yes, it DOES NOT have a large metal compression “fork spring” or set of fork springs as you would find in a fork that we are more familiar with, but that does not mean that it’s a “spring free” or a “spring-less” fork. In fact, it would also be incorrect to refer to the 2013 PSF fork as a pneumatic fork, as all fork designs prior to this have a pneumatic component as part of their design and, well…we don’t want to lose any respect for that.
Say what?
First off, the PSF still has a metal spring in the fork called a “balance spring” or “top out spring”. In fact, technically, it has four of these, two in each side. You could also call this a “counter spring” as it counters some of the forces applied by the compressed air. You will feel and see the effects of the balance-spring if you remove the fork from the bike and let all the air out – as the air is let out, the fork sucks down. No joke. More on this later.
Now…the other part to this madness is defining what a “spring-less” fork is because all forks and shocks often have a mixture of metal springs and air springs. So…the 2012 CRF450R had a total of six metal springs (not counting the “valving” mechanisms) and two air springs. The 2013 CRF450R has four metal springs and two air springs. And just to make things really interesting, the 06-12 YZs and the 06-12 KX450F has four air springs, and six metal springs. Those numbers will surprise or confuse a few suspension guys.
By the way, when you add or remove fork oil, in the lower chamber of a closed cartridge fork or the open bath chamber of the USDs, you are, in effect, adjusting the “air spring”.
So…no problem running about the track calling the PSF an “air fork” but let’s not get too carried away in thinking that this is some sort of radical approach to using air instead of a spring.
So…air verses a metal spring?
What is really important to understand in answering this question is the dynamics of progression. Progression is a rate of change based on position. So…as you compress a fork, it becomes harder and harder to compress. How much harder it becomes, each additional millimeter, is a measurement of the fork’s progression rate. Now...in most cases, suspension guys refer to progression as a change that follows a linear rate, meaning that it doubles in force for each equal increment in compression. So…if one inch of compression takes 10 pounds of force, then two inches of compression should take 20 pounds of force. So…we usually think of linear rates as a normal or expected path, and then use that as a guide to figure out how radical the rate changes when it becomes non-linear.
So why does that matter?
So…now we get into some interesting stuff. On the most part, metal springs are designed to progress at a linear rate…and out of our control, the compression of air of a gas compresses at a non-linear rate. So that’s means that you have to do some interesting things to get a fork to behave like we want or need when the metal spring is removed. This is the reason why the PSF has a counter-spring – they are using a metal spring to counter the early progression of forces that are related to the compression of air. So there.
So what happens to a PSF if the fork seals leak?
In short, you’re hosed. In fact, it’s worse than what people realize. Here’s why. First, most of the PSF forks will be operating with a pressure rating between 33 to 40 PSI. Additionally, there is not a lot of volume involved. What that means is that even a small fork leak will have a dramatic effect. AND…making matters worse, the more air you lose, the more the counter or balance spring is going to want to pull (yes, PULL!) the bike down. So…if the fork seal leaks, you are in trouble and most likely your day it done.
Could a leaky fork seal cause me to lose a race or have to pull out?
Very much. A change in pressure, of even just a pound or two of air, is the equivalent of changing your forks springs from something very stiff to something very soft. Imagine racing and going from a .48KG spring to a .42KG spring within a few laps? That could make certain jump launches and whoop sections very tricky if not completely impossible to hit at any speed. You could also have a severe failure which would quickly end your day….and could possible mean that you won’t be going home in something that doesn’t have flashing lights on top of it.
Yikes! What were they thinking?!?!
So…this is when it’s going to sting just a bit. In the world of business and manufacturing there is this thing called, “COGS”, which is short for “Cost of goods sold”. It is the cost of the material that a manufacture uses to assemble the bike. So…if Honda purchases a bolt for $2 and last year it cost $3, their COGS went down $1 and that means they make $1 more per bike this year than last. NOW…the driving factor for the PSF, (and the SFF) was to reduce to cost, and the driving factor for reducing COGS was the recession that started in 2008, which hit manufactures VERY hard. So...the PSF is not about evolving the technology, it’s about reducing costs. HOWEVER, if you can evolve the technology some small amount and also reduce cost, then it’s a good thing. But…we are giving up reliability to gain a small margin of performance.
Is the PSF a better fork than the standard SSS?
Not really…I mean, it’s here and it’s not going away. The PSF can certainly be tuned to operate as a better fork, and performance wise, it might be better out of the box as a SSS, but…in the real world, in which most of us spend some money to tune our suspensions, the SSS has a big advantage.
Is the PSF not an engineering marvel?
It is not. In fact, if you started with a clean slate of designing a “spring-less” fork that offered maximum performance, this would not be the design. This may have something to do with why Yamaha is not on board with the PSF, (just assuming). However, it’s a great compromise between performance and keeping the cost of a bike low. The 2013-14 SHOWA SFF A-Kit is a much better example of a pneumatic fork that is ideally engineered. There are also a collection of high-end downhill mountain bike forks that offer much more performance over cost reduction.
Does the PSF use the same main seal as other forks?
No. It is a new seal that seals better and will last longer. However, it also has a higher static friction rating than a 06-12 seal.
Could I use a standard seal from a 48mm KYB fork?
Yes…and no. Yes, in that it will fit and work, but…as with most things, there is always a balancing act between durability and performance. I'm sure we are not too far off from suspension companies coming out with a "PSF seal" with various claims. To be honest with you, SKF makes a 48mmHD seal, (part number KIT48KHD) which would really be the best seal for the PSF. I would upgrade to this...day one.
Is there something that can be done to keep the fork from failing if the fork seal fails?
Not really. I mean, you could create something that seals the inner cartridge from the main seal but all that means is that you just have two seals, which is not much different than just having one seal with multiple sealing lips. So again, durability and performance. And certainly, anything that happens with the fork tube (nick or dent) is going to cause a leak regardless of the seal or number of seals. I mean, this is a telescopic fork, so…you can run…but you can’t hide.
Is there anything I can do to make a fork seal last longer and/or not fail?
Yes…don’t wash your bike.
Say what?
When you wash a bike you wash away a layer of oil on the lower tube (and shock shaft) that actually helps the seal to seal and to stay healthy. Additionally, when most riders wash their bikes they leave water behind on the lower tube and due to the minerals in hard water, that’s like leaving little sanding pads on the fork that are destined to destroy a seal. The moral of the story? If and when you wash a bike, clean the suspension chrome (front and rear) of any water and then lube the tube. A rag with some suspension fluid is best. WD-40 is the worst, (it's a reactive solvent that destroys seals). And never spray anything around a brake rotor.
Can I take a PSF and easily convert it to a metal compression spring type set-up, as in last year with the SSS fork?
Easy and low cost? No. You can’t simply just drop in last year’s cartridges with a spring, which if you could, would run you about $1000 if you purchase the parts from a dealer. In other words, there is no quick fix to this issue.
Will the fork change as the outside air warms up, or as the fork warms up?
Yes…and this too will be a big problem for some riders. All gases follow what is called “ideal gas laws” and that means that as temperatures change, or as you change altitude, the effective spring rate of the fork will change…and to be honest with you, it won’t take much. So…in some cases, you may need to adjust the air in the fork two to three times per track day ride. Even the use of the front brake will heat the fork and cause the spring rate to change. So…expect more build-up in the right fork leg than the left.
Will running nitrogen in the fork help?
Yes and no. Nitrogen will still rise in pressure as outside air or any gas does, (still follows the same laws) however, nitrogen inherently runs cooler because it takes more energy to heat it up. Neat…eh?
What was the deal with Pro Circuit saying that the fork didn’t change much when they lost air?
They were not talking about the KYB-PSF, but were referring to the 2013-14 SHOWA SFF A-kit that they are testing, which is a very different fork.
So why does the SFF A-kit not fall down into the stroke when lower chamber pressure is reduced?
Because it has different chambers, each of which are pressurized. So...redundancy. And I would assume that is does not have any counter/balance springs.
Let me know what questions you guys have and I’ll try and address them.
Dave Johnson
SMART Performance Inc.
Dave.johnson@smartperformanceinc.com
408-406-2089
in short, if they leak, you are done. no wiping off your leaky oil and riding the rest of the day. 2. it will pretty much just collapse. also it actually sucks the front end down. imagine that happening on the face of a jump. good things? tuneable..
interesting view on the costs of it, didnt really think about it like that. makes sense to me.
whats everyone else think?
-------------
Here are some things that may help to better understand the new 2013 PSF forks. This applies to both the 2013 CRF450R and the 2013 KX450F.
What is the PSF?
It is a fork that is more of a pneumatic or air fork than last year, but it is not a “spring-less” fork. Yes, it DOES NOT have a large metal compression “fork spring” or set of fork springs as you would find in a fork that we are more familiar with, but that does not mean that it’s a “spring free” or a “spring-less” fork. In fact, it would also be incorrect to refer to the 2013 PSF fork as a pneumatic fork, as all fork designs prior to this have a pneumatic component as part of their design and, well…we don’t want to lose any respect for that.
Say what?
First off, the PSF still has a metal spring in the fork called a “balance spring” or “top out spring”. In fact, technically, it has four of these, two in each side. You could also call this a “counter spring” as it counters some of the forces applied by the compressed air. You will feel and see the effects of the balance-spring if you remove the fork from the bike and let all the air out – as the air is let out, the fork sucks down. No joke. More on this later.
Now…the other part to this madness is defining what a “spring-less” fork is because all forks and shocks often have a mixture of metal springs and air springs. So…the 2012 CRF450R had a total of six metal springs (not counting the “valving” mechanisms) and two air springs. The 2013 CRF450R has four metal springs and two air springs. And just to make things really interesting, the 06-12 YZs and the 06-12 KX450F has four air springs, and six metal springs. Those numbers will surprise or confuse a few suspension guys.
By the way, when you add or remove fork oil, in the lower chamber of a closed cartridge fork or the open bath chamber of the USDs, you are, in effect, adjusting the “air spring”.
So…no problem running about the track calling the PSF an “air fork” but let’s not get too carried away in thinking that this is some sort of radical approach to using air instead of a spring.
So…air verses a metal spring?
What is really important to understand in answering this question is the dynamics of progression. Progression is a rate of change based on position. So…as you compress a fork, it becomes harder and harder to compress. How much harder it becomes, each additional millimeter, is a measurement of the fork’s progression rate. Now...in most cases, suspension guys refer to progression as a change that follows a linear rate, meaning that it doubles in force for each equal increment in compression. So…if one inch of compression takes 10 pounds of force, then two inches of compression should take 20 pounds of force. So…we usually think of linear rates as a normal or expected path, and then use that as a guide to figure out how radical the rate changes when it becomes non-linear.
So why does that matter?
So…now we get into some interesting stuff. On the most part, metal springs are designed to progress at a linear rate…and out of our control, the compression of air of a gas compresses at a non-linear rate. So that’s means that you have to do some interesting things to get a fork to behave like we want or need when the metal spring is removed. This is the reason why the PSF has a counter-spring – they are using a metal spring to counter the early progression of forces that are related to the compression of air. So there.
So what happens to a PSF if the fork seals leak?
In short, you’re hosed. In fact, it’s worse than what people realize. Here’s why. First, most of the PSF forks will be operating with a pressure rating between 33 to 40 PSI. Additionally, there is not a lot of volume involved. What that means is that even a small fork leak will have a dramatic effect. AND…making matters worse, the more air you lose, the more the counter or balance spring is going to want to pull (yes, PULL!) the bike down. So…if the fork seal leaks, you are in trouble and most likely your day it done.
Could a leaky fork seal cause me to lose a race or have to pull out?
Very much. A change in pressure, of even just a pound or two of air, is the equivalent of changing your forks springs from something very stiff to something very soft. Imagine racing and going from a .48KG spring to a .42KG spring within a few laps? That could make certain jump launches and whoop sections very tricky if not completely impossible to hit at any speed. You could also have a severe failure which would quickly end your day….and could possible mean that you won’t be going home in something that doesn’t have flashing lights on top of it.
Yikes! What were they thinking?!?!
So…this is when it’s going to sting just a bit. In the world of business and manufacturing there is this thing called, “COGS”, which is short for “Cost of goods sold”. It is the cost of the material that a manufacture uses to assemble the bike. So…if Honda purchases a bolt for $2 and last year it cost $3, their COGS went down $1 and that means they make $1 more per bike this year than last. NOW…the driving factor for the PSF, (and the SFF) was to reduce to cost, and the driving factor for reducing COGS was the recession that started in 2008, which hit manufactures VERY hard. So...the PSF is not about evolving the technology, it’s about reducing costs. HOWEVER, if you can evolve the technology some small amount and also reduce cost, then it’s a good thing. But…we are giving up reliability to gain a small margin of performance.
Is the PSF a better fork than the standard SSS?
Not really…I mean, it’s here and it’s not going away. The PSF can certainly be tuned to operate as a better fork, and performance wise, it might be better out of the box as a SSS, but…in the real world, in which most of us spend some money to tune our suspensions, the SSS has a big advantage.
Is the PSF not an engineering marvel?
It is not. In fact, if you started with a clean slate of designing a “spring-less” fork that offered maximum performance, this would not be the design. This may have something to do with why Yamaha is not on board with the PSF, (just assuming). However, it’s a great compromise between performance and keeping the cost of a bike low. The 2013-14 SHOWA SFF A-Kit is a much better example of a pneumatic fork that is ideally engineered. There are also a collection of high-end downhill mountain bike forks that offer much more performance over cost reduction.
Does the PSF use the same main seal as other forks?
No. It is a new seal that seals better and will last longer. However, it also has a higher static friction rating than a 06-12 seal.
Could I use a standard seal from a 48mm KYB fork?
Yes…and no. Yes, in that it will fit and work, but…as with most things, there is always a balancing act between durability and performance. I'm sure we are not too far off from suspension companies coming out with a "PSF seal" with various claims. To be honest with you, SKF makes a 48mmHD seal, (part number KIT48KHD) which would really be the best seal for the PSF. I would upgrade to this...day one.
Is there something that can be done to keep the fork from failing if the fork seal fails?
Not really. I mean, you could create something that seals the inner cartridge from the main seal but all that means is that you just have two seals, which is not much different than just having one seal with multiple sealing lips. So again, durability and performance. And certainly, anything that happens with the fork tube (nick or dent) is going to cause a leak regardless of the seal or number of seals. I mean, this is a telescopic fork, so…you can run…but you can’t hide.
Is there anything I can do to make a fork seal last longer and/or not fail?
Yes…don’t wash your bike.
Say what?
When you wash a bike you wash away a layer of oil on the lower tube (and shock shaft) that actually helps the seal to seal and to stay healthy. Additionally, when most riders wash their bikes they leave water behind on the lower tube and due to the minerals in hard water, that’s like leaving little sanding pads on the fork that are destined to destroy a seal. The moral of the story? If and when you wash a bike, clean the suspension chrome (front and rear) of any water and then lube the tube. A rag with some suspension fluid is best. WD-40 is the worst, (it's a reactive solvent that destroys seals). And never spray anything around a brake rotor.
Can I take a PSF and easily convert it to a metal compression spring type set-up, as in last year with the SSS fork?
Easy and low cost? No. You can’t simply just drop in last year’s cartridges with a spring, which if you could, would run you about $1000 if you purchase the parts from a dealer. In other words, there is no quick fix to this issue.
Will the fork change as the outside air warms up, or as the fork warms up?
Yes…and this too will be a big problem for some riders. All gases follow what is called “ideal gas laws” and that means that as temperatures change, or as you change altitude, the effective spring rate of the fork will change…and to be honest with you, it won’t take much. So…in some cases, you may need to adjust the air in the fork two to three times per track day ride. Even the use of the front brake will heat the fork and cause the spring rate to change. So…expect more build-up in the right fork leg than the left.
Will running nitrogen in the fork help?
Yes and no. Nitrogen will still rise in pressure as outside air or any gas does, (still follows the same laws) however, nitrogen inherently runs cooler because it takes more energy to heat it up. Neat…eh?
What was the deal with Pro Circuit saying that the fork didn’t change much when they lost air?
They were not talking about the KYB-PSF, but were referring to the 2013-14 SHOWA SFF A-kit that they are testing, which is a very different fork.
So why does the SFF A-kit not fall down into the stroke when lower chamber pressure is reduced?
Because it has different chambers, each of which are pressurized. So...redundancy. And I would assume that is does not have any counter/balance springs.
Let me know what questions you guys have and I’ll try and address them.
Dave Johnson
SMART Performance Inc.
Dave.johnson@smartperformanceinc.com
408-406-2089
