Seeing strokedtater's for sale thread and some questioning about the difference, I figured I would get the information on their site and post it here so it can answer any questions...
SPRINGS
The spring is (for the most part) wound steel and is defined by its rate.
Rate is a measurement of the force required to compress the spring and is expressed in lbs per inch. For instance a spring with a 100 lbs/inch rate will require 100 lbs to compress it one inch. Each subsequent inch of compression would require an additional 100lbs of force. This is referred to as a straight or linear rate spring. The alternative, is a progressive rate spring which allows a single spring to essentially exhibit multiple rates. By utilizing varied spacing spring coils, the initial rate may be 60lbs/inch, requiring 60 lbs of force to compress it one inch. Then each subsequent inch of movement would require progressively more than 60lbs of force such as 75lbs more for the second inch, 100lbs more for the third inch etc, as shown in the example. Progressive-rate springs become stiffer quicker as they are compressed. The advantage is a spring that is supple enough to soak up small bumps, yet firm enough to handle a big hit.
DAMPERS
Now that your motorcycle has “absorbed” a bump, the compressed spring has stored the energy of the hit and without a damper it would be released in a fury of rebound might, extending the spring beyond its original static length and repeating the cycle until the energy had dissipated. The resultant store and release sequence would cause your bike to pogo down the road. Imagine a basketball bounced hard onto the asphalt, not only does it bounce back, but it would bounce higher than your hands where it had started. Now, imagine if you bounced it under water. This is the effect that a damper has on the stored energy of a spring. In fact, a damper, like the water analogy, uses a liquid (in this case oil) and forces it through a series of small holes. The ensuing resistance controls the return of the spring energy. The kinetic energy (motion) of the spring is transferred to the oil and dissipated as heat. Oil based damping is a clever solution, yet comes with its own set of challenges. For instance, rapid damper movement reduces the space within the shock for the fluid, thus a compressible medium must come into play or the shock would likely stop moving. The obvious solution would be to leave a bit of air space for the oil to move into, but air rapidly expands when heated (remember the shock has transferred the energy of motion to heat) and the damping characteristics of the shock would be ever changing. The solution is a separate chamber of a heat tolerant gas (in this case nitrogen) that allows the oil to expand without impacting the damping.
PRELOAD ADJUSTMENT
All of Progressive Suspension’s shocks are Preload Adjustable. This allows the user to easily tune the shocks for their specific combination of bike and rider weight. Although we design a shock to fit and perform on a specific motorcycle, we have no way of knowing if the rider will be 140lb or 240lb and the addition of cargo and passenger further complicates the issue. An obvious solution is an adjustment on the shock that allows the rider to quickly set up his shocks to match his bike/rider weight combination. This is where Preload Adjustment comes into play. By compressing or uncompressing the spring a small amount, a shock can be perfectly tuned to suit the conditions for which it will be used. In addition to this level of tuning, most PSI shocks are also offered in Heavy Duty applications, recommended for bikes that are operated at or near the manufacturer’s maximum load rating over 50% of the time.
SAG ADJUSTMENT
OK, so now you know your shocks can be adjusted to fit your bike and weight, but where do you start? Naturally from the beginning and with an understanding that shocks work in both the up and down movements of the bike. If all pavement imperfections where bumps, shocks for the most part would focus on compression. Unfortunately, there are pot holes and other sorts of gaps that require a shock to function in the other direction, as well. To achieve this, a shock compresses a small amount under the weight of the bike and the rider, before it has even been asked to do any work. This is called Sag, and is adjusted via the handy Preload Adjusters we include on each PSI shock. There are two key Sag measurements, the first is Free Sag, ideally measured from the center of the rear axle to an arbitrary point directly above the axle (a fender bracket, for instance). This is done off the stand and with a helper holding the bike straight up. A solid lift of the rear end (simply pick up the bike by the fender or rack as far as you can) will unladen the shocks and a Free Sag measurement can be taken. The next critical measurement is Rider Sag and this is done with the rider on the bike (hands on the bars and feet on the pegs) and a helper or two supporting it. A measurement is again taken from the center of the rear axle to the same point as before. The difference between the two measurements is your final Sag and for cruiser and touring bikes is generally expected to be .75” to 1.25” (depending on application). If your number is less, then the bike will require less preload, and if it is higher, more preload is needed. Twin shock bikes should always be adjusted with the equal preload on both sides.
This article was for motorcycles, but it you can relate it to a quad quite easily. This was all pulled off of Progressive Suspension's website, found here. Hopefully it helps someone.
SPRINGS
The spring is (for the most part) wound steel and is defined by its rate.
Rate is a measurement of the force required to compress the spring and is expressed in lbs per inch. For instance a spring with a 100 lbs/inch rate will require 100 lbs to compress it one inch. Each subsequent inch of compression would require an additional 100lbs of force. This is referred to as a straight or linear rate spring. The alternative, is a progressive rate spring which allows a single spring to essentially exhibit multiple rates. By utilizing varied spacing spring coils, the initial rate may be 60lbs/inch, requiring 60 lbs of force to compress it one inch. Then each subsequent inch of movement would require progressively more than 60lbs of force such as 75lbs more for the second inch, 100lbs more for the third inch etc, as shown in the example. Progressive-rate springs become stiffer quicker as they are compressed. The advantage is a spring that is supple enough to soak up small bumps, yet firm enough to handle a big hit.
DAMPERS
Now that your motorcycle has “absorbed” a bump, the compressed spring has stored the energy of the hit and without a damper it would be released in a fury of rebound might, extending the spring beyond its original static length and repeating the cycle until the energy had dissipated. The resultant store and release sequence would cause your bike to pogo down the road. Imagine a basketball bounced hard onto the asphalt, not only does it bounce back, but it would bounce higher than your hands where it had started. Now, imagine if you bounced it under water. This is the effect that a damper has on the stored energy of a spring. In fact, a damper, like the water analogy, uses a liquid (in this case oil) and forces it through a series of small holes. The ensuing resistance controls the return of the spring energy. The kinetic energy (motion) of the spring is transferred to the oil and dissipated as heat. Oil based damping is a clever solution, yet comes with its own set of challenges. For instance, rapid damper movement reduces the space within the shock for the fluid, thus a compressible medium must come into play or the shock would likely stop moving. The obvious solution would be to leave a bit of air space for the oil to move into, but air rapidly expands when heated (remember the shock has transferred the energy of motion to heat) and the damping characteristics of the shock would be ever changing. The solution is a separate chamber of a heat tolerant gas (in this case nitrogen) that allows the oil to expand without impacting the damping.
PRELOAD ADJUSTMENT
All of Progressive Suspension’s shocks are Preload Adjustable. This allows the user to easily tune the shocks for their specific combination of bike and rider weight. Although we design a shock to fit and perform on a specific motorcycle, we have no way of knowing if the rider will be 140lb or 240lb and the addition of cargo and passenger further complicates the issue. An obvious solution is an adjustment on the shock that allows the rider to quickly set up his shocks to match his bike/rider weight combination. This is where Preload Adjustment comes into play. By compressing or uncompressing the spring a small amount, a shock can be perfectly tuned to suit the conditions for which it will be used. In addition to this level of tuning, most PSI shocks are also offered in Heavy Duty applications, recommended for bikes that are operated at or near the manufacturer’s maximum load rating over 50% of the time.
SAG ADJUSTMENT
OK, so now you know your shocks can be adjusted to fit your bike and weight, but where do you start? Naturally from the beginning and with an understanding that shocks work in both the up and down movements of the bike. If all pavement imperfections where bumps, shocks for the most part would focus on compression. Unfortunately, there are pot holes and other sorts of gaps that require a shock to function in the other direction, as well. To achieve this, a shock compresses a small amount under the weight of the bike and the rider, before it has even been asked to do any work. This is called Sag, and is adjusted via the handy Preload Adjusters we include on each PSI shock. There are two key Sag measurements, the first is Free Sag, ideally measured from the center of the rear axle to an arbitrary point directly above the axle (a fender bracket, for instance). This is done off the stand and with a helper holding the bike straight up. A solid lift of the rear end (simply pick up the bike by the fender or rack as far as you can) will unladen the shocks and a Free Sag measurement can be taken. The next critical measurement is Rider Sag and this is done with the rider on the bike (hands on the bars and feet on the pegs) and a helper or two supporting it. A measurement is again taken from the center of the rear axle to the same point as before. The difference between the two measurements is your final Sag and for cruiser and touring bikes is generally expected to be .75” to 1.25” (depending on application). If your number is less, then the bike will require less preload, and if it is higher, more preload is needed. Twin shock bikes should always be adjusted with the equal preload on both sides.
This article was for motorcycles, but it you can relate it to a quad quite easily. This was all pulled off of Progressive Suspension's website, found here. Hopefully it helps someone.
