sportryder
Well-known member
Kevin,
Let me try to explain spring preload and then spring rate. They are often highly misunderstood.
Lets take a spring and remove it from a shock and let it stand alone in a static position. It has 0 (zero) preload applied to it at this point. Now, lets give that spring a spring rate in lb/inches so we can use that rate to describe what happens when we apply some preload to the spring. We'll use a nice even number that will make it easy to do some calculations. Let's say the spring has a rate of 500 lb/inch. Now, we'll apply 1/2 inch of preload to it after we install it on a shock. When it is installed on a shock with a threaded collar it's possible to still have 0 preload applied. Now, we'll start compressing that spring but the shock is still fully extended or topped out as we would call it. We'll apply 1/2 inch of preload or compress it with the preload collar by that amount. When we have 1/2 inch of preload applied, the shock spring is exerting 250 lbs of force on the preload collar at this point and 250 lbs of force outwards on the spring perch at the other end of the spring. The spring is captured between the preload collar and the spring perch. In other words, 250 lbs of force is exerted outwards and would be the starting amount of force pushing on whatever this shock might support. If we were to apply another 1/2 inch of preload to the spring by turning the threaded collar down to compress the spring further, we would have a full 1 inch of preload on the spring. With 1 inch of preload, there is 500 lbs of force pushing outwards.
The rate of 500 lbs per inch will not change with a straight rate or "linear" spring even if we compressed the spring another inch and another inch after that. With 2 inches of spring compression, the spring would be exerting a force of 1000 lbs outwards on the preload collar and the spring perch at the other end. At 3 inches of spring compression, the spring would exert 1500 lbs of force outwards.
One would never use 3 inchs of preload on a spring. If they did, they would be a fool to do so and the shock probably would not compress. So, in simple terms, spring preload is used to modify the starting point for the exertion of force in lbs.
If we were to use a 1000 lb/inch spring, we could preload it 1/4 of an inch and have the same starting force as we did earlier by preloading a 500 lb/inch spring by 1/2 inch. Are you still with me here? I might be babbling jibberish but this is the only way that I know of to explain how the amount of spring preload will vary by using two different rate springs.
Now, let me draw another picture for you. It may help clarify why using a soft spring with more preload is not as good as using a stiffer spring with less preload. Motorcycle suspensions react differently than car suspensions because of the way a motorcycle goes around a corner. When a motorcycle corners, there are no lateral G-forces. Why? because a single track vehicle would fall over towards the outside of the turn if it did. When a motorcycle turns at speed, it banks over similar to how an airplane turns. Because of this banking over, the G-forces or load goes straight down through the chassis and suspension to the tire contact patch. Because of this G-loading, the suspension will compress more. If the spring was too soft, the suspension would compress so much that ground clearance would be reduced quite a bit and suspension travel would also be reduced to a point where there was very little travel remaining in order to soak up a bump. Well, someone might think - I'll just increase the starting force by adding preload to the spring. That way, it'll give me less resistance to spring compression during these moments of severe chassis loading and G-forces while cornering. Well, it might do that but what happens to the ride of the bike while you are not G-loading the chassis and going straight down the road. Remember what we said in the paragraph above? Increasing the starting force is what preloading the spring does? The result would be -> the ride would be unbearable with a lot of preload on the spring. The suspension would be topped out and it would initially feel very stiff. This is exactly why a suspension tuner uses a tool called "sag measurement". We have determined that a certain amount of chassis sag on a motorcycle will help define what the proper spring rate should be for a certain weight motorcycle. If a spring has to have more than a certain amount of preload applied to it in order to get inside the ballpark for this range of chassis sag, then the spring is too soft for the application. The inverse is also true - if a spring has too little preload on it in order for the chassis to sag within this range then the spring is too stiff. Measurement of sag is simply a tool to get the chassis dynamics sorted so the motorcycle or vehicle has certain handling and ride characteristics. The overall goal is to use a spring that is stiff enough to provide ample suspension bottoming resistance during cornering or higher than normal G-loading, yet provide a soft and supple ride when the suspension is not being G-loaded or while riding/driving straight down the road. It might sound strange, but in many cases with motorcycles, using a stiffer spring but preloading it less will provide a softer "feeling" ride than using a softer spring and using a LOT more preload.
There is a trade-off at times and compromises need to be made. It's not always about measuring sag or using sag numbers. An example of that is the FJR. The classic sag numbers that we would use for a race bike do not work real well on all motorcycles. When I first started doing shock and spring testing with the FJR, I tried a 950 lb/inch spring because it was recommended to me by a guy out on the west coast that had set up several FJRs. We had no hands on data at our shop. He said the sag numbers were nearly perfect with a 200-210 lb rider on board. In fact, he mentioned that possibly a 1000 lb spring might be better if I did much 2-up riding. Well, that 950 lb spring was BRUTAL! So, I threw an 800 lb spring on it and increased the preload. The ride was much better but during cornering, the chassis wanted to wallow just a bit and the amount of preload was starting to get up to the amount where we would consider it being at the borderline for too much preload being needed. Sag numbers were starting to get outside our recommended range too. So, I thought at that point the 850 lb/inch spring would be the standard spring for someone weighing what I did and also had similiar riding requirements. The ride was acceptable over most all but the larger bumps yet the bike handled the cornering G-loads very well. The final sag numbers are just outside of our recommended range. Sag numbers don't have to live with the bike and ride it. I do.
This is something one should never forget. Sag measurement is simply a tool to use in order to proceed in the proper direction for setting up a street bike. It's not written in stone and it doesn't ride the bike. Pavement surface conditions may vary a substantial amount too. It's not a plug and chug formula for nirvana. X amount of sag means it will handle and ride perfectly. Much too many variables for that with a street bike.
I hope this lengthy text will help explain spring rates, what spring preload is, and how the two of them work together in order to setup a motorcycle suspension.
Something I was told early on when I first started working at Traxxion. "A soft spring with a lot of preload on it only gives the "illusion" that the motorcycle will handle better. The spring will still function at the same rate of lbs per inch of spring compression, you've only elevated the starting amount of force being exerted outwards on whatever that shock/spring is supporting."
The relay arm is what the dogbones and shock attach to at the bottom of the shock. The distance between the pivoting points (shape of the "L" or triangle as you call it) is different with the Gen2 FJR. Yamaha has used different geometry to work with the longer swingarm and the stiffer short spring used in series with the longer spring on the SOFT setting.
I hope all of my jibberish has not confused you further. I do that sometimes even though I try to be as clear as I can with my explainations. Time to go to bed now.... I've been typing for a couple of hours.
Let me try to explain spring preload and then spring rate. They are often highly misunderstood.
Lets take a spring and remove it from a shock and let it stand alone in a static position. It has 0 (zero) preload applied to it at this point. Now, lets give that spring a spring rate in lb/inches so we can use that rate to describe what happens when we apply some preload to the spring. We'll use a nice even number that will make it easy to do some calculations. Let's say the spring has a rate of 500 lb/inch. Now, we'll apply 1/2 inch of preload to it after we install it on a shock. When it is installed on a shock with a threaded collar it's possible to still have 0 preload applied. Now, we'll start compressing that spring but the shock is still fully extended or topped out as we would call it. We'll apply 1/2 inch of preload or compress it with the preload collar by that amount. When we have 1/2 inch of preload applied, the shock spring is exerting 250 lbs of force on the preload collar at this point and 250 lbs of force outwards on the spring perch at the other end of the spring. The spring is captured between the preload collar and the spring perch. In other words, 250 lbs of force is exerted outwards and would be the starting amount of force pushing on whatever this shock might support. If we were to apply another 1/2 inch of preload to the spring by turning the threaded collar down to compress the spring further, we would have a full 1 inch of preload on the spring. With 1 inch of preload, there is 500 lbs of force pushing outwards.
The rate of 500 lbs per inch will not change with a straight rate or "linear" spring even if we compressed the spring another inch and another inch after that. With 2 inches of spring compression, the spring would be exerting a force of 1000 lbs outwards on the preload collar and the spring perch at the other end. At 3 inches of spring compression, the spring would exert 1500 lbs of force outwards.
One would never use 3 inchs of preload on a spring. If they did, they would be a fool to do so and the shock probably would not compress. So, in simple terms, spring preload is used to modify the starting point for the exertion of force in lbs.
If we were to use a 1000 lb/inch spring, we could preload it 1/4 of an inch and have the same starting force as we did earlier by preloading a 500 lb/inch spring by 1/2 inch. Are you still with me here? I might be babbling jibberish but this is the only way that I know of to explain how the amount of spring preload will vary by using two different rate springs.
Now, let me draw another picture for you. It may help clarify why using a soft spring with more preload is not as good as using a stiffer spring with less preload. Motorcycle suspensions react differently than car suspensions because of the way a motorcycle goes around a corner. When a motorcycle corners, there are no lateral G-forces. Why? because a single track vehicle would fall over towards the outside of the turn if it did. When a motorcycle turns at speed, it banks over similar to how an airplane turns. Because of this banking over, the G-forces or load goes straight down through the chassis and suspension to the tire contact patch. Because of this G-loading, the suspension will compress more. If the spring was too soft, the suspension would compress so much that ground clearance would be reduced quite a bit and suspension travel would also be reduced to a point where there was very little travel remaining in order to soak up a bump. Well, someone might think - I'll just increase the starting force by adding preload to the spring. That way, it'll give me less resistance to spring compression during these moments of severe chassis loading and G-forces while cornering. Well, it might do that but what happens to the ride of the bike while you are not G-loading the chassis and going straight down the road. Remember what we said in the paragraph above? Increasing the starting force is what preloading the spring does? The result would be -> the ride would be unbearable with a lot of preload on the spring. The suspension would be topped out and it would initially feel very stiff. This is exactly why a suspension tuner uses a tool called "sag measurement". We have determined that a certain amount of chassis sag on a motorcycle will help define what the proper spring rate should be for a certain weight motorcycle. If a spring has to have more than a certain amount of preload applied to it in order to get inside the ballpark for this range of chassis sag, then the spring is too soft for the application. The inverse is also true - if a spring has too little preload on it in order for the chassis to sag within this range then the spring is too stiff. Measurement of sag is simply a tool to get the chassis dynamics sorted so the motorcycle or vehicle has certain handling and ride characteristics. The overall goal is to use a spring that is stiff enough to provide ample suspension bottoming resistance during cornering or higher than normal G-loading, yet provide a soft and supple ride when the suspension is not being G-loaded or while riding/driving straight down the road. It might sound strange, but in many cases with motorcycles, using a stiffer spring but preloading it less will provide a softer "feeling" ride than using a softer spring and using a LOT more preload.
There is a trade-off at times and compromises need to be made. It's not always about measuring sag or using sag numbers. An example of that is the FJR. The classic sag numbers that we would use for a race bike do not work real well on all motorcycles. When I first started doing shock and spring testing with the FJR, I tried a 950 lb/inch spring because it was recommended to me by a guy out on the west coast that had set up several FJRs. We had no hands on data at our shop. He said the sag numbers were nearly perfect with a 200-210 lb rider on board. In fact, he mentioned that possibly a 1000 lb spring might be better if I did much 2-up riding. Well, that 950 lb spring was BRUTAL! So, I threw an 800 lb spring on it and increased the preload. The ride was much better but during cornering, the chassis wanted to wallow just a bit and the amount of preload was starting to get up to the amount where we would consider it being at the borderline for too much preload being needed. Sag numbers were starting to get outside our recommended range too. So, I thought at that point the 850 lb/inch spring would be the standard spring for someone weighing what I did and also had similiar riding requirements. The ride was acceptable over most all but the larger bumps yet the bike handled the cornering G-loads very well. The final sag numbers are just outside of our recommended range. Sag numbers don't have to live with the bike and ride it. I do.
This is something one should never forget. Sag measurement is simply a tool to use in order to proceed in the proper direction for setting up a street bike. It's not written in stone and it doesn't ride the bike. Pavement surface conditions may vary a substantial amount too. It's not a plug and chug formula for nirvana. X amount of sag means it will handle and ride perfectly. Much too many variables for that with a street bike.I hope this lengthy text will help explain spring rates, what spring preload is, and how the two of them work together in order to setup a motorcycle suspension.
Something I was told early on when I first started working at Traxxion. "A soft spring with a lot of preload on it only gives the "illusion" that the motorcycle will handle better. The spring will still function at the same rate of lbs per inch of spring compression, you've only elevated the starting amount of force being exerted outwards on whatever that shock/spring is supporting."
The relay arm is what the dogbones and shock attach to at the bottom of the shock. The distance between the pivoting points (shape of the "L" or triangle as you call it) is different with the Gen2 FJR. Yamaha has used different geometry to work with the longer swingarm and the stiffer short spring used in series with the longer spring on the SOFT setting.
I hope all of my jibberish has not confused you further. I do that sometimes even though I try to be as clear as I can with my explainations. Time to go to bed now.... I've been typing for a couple of hours.
Right so, what you are saying is that the advantage of the aftermarket is more flexibility/variability in the total preload options. Thats a valid point but I guess what I dont understand is the difference between preload and spring rate. I mean preload is how much you compress the spring but is spring rate how much force it takes to deform the spring to some criterion?
I am also curious about this L-shaped arm you mention; are you refering to the pivot triangle that the shock connects to? How did they change it? just a curiosity.
I think too you have very elegantly pointed out the tradeoff between the stock and aftermarket shocks. If I had my druthers and the cash, I would certianly take a nice aftermarket shock (Seriously, somebody send me one and I'll write up a review with some pics and stuff
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