New Dinan Tech Article About Suspension Travel and the M3

[e46e92love]

Originally Posted by Gearhead999s

H&R have no clue about bump stops being part of the springing package.I had a MarkV GTI that I put H&R springs on it and it was a disaster riding the bump stops all the time and handled like crap all the time.Contacted H& R to try to get some answers and they did not understand what my problem was.Put the Euro springs on with the proper bump stops and all was good.Lower is not nessarily the better way to go if you actually care about handling,not athestics.Dinan are on the right track on this.

+1

[e46e92love]

Originally Posted by lucid

The Dinan article combined with observations like Gearhead's really puts this garden variety aftermarket "buy my stuff it works" BS in context. How much research does a spring company really need to do to understand some of the basics like suspension travel and bump stops, etc.? How can these "highly recommended" manufacturers miss out on all this? (Assuming the information Dinan folks are providing is true. I would take their words over H&R's on this. The man is making a formal decleration on the internet with an account in his name and his professional association, so he must know what he is talking about).

And folks who get the H&R upgrade often say their cars now "handle better". I made several posts on that topic, saying "most people who pay a grand for the entire deal of course will come back and say it sure handles better now, what do you expect?" and asked for some objective performance assessment, and I was told things like my friend who installed this really knows about cars and he thinks it makes the car go faster because it is stiffer and turn in is better, etc. I guess it is fine to do it for looks, but one should think more carefully about the performance part. But then you've got shops like Turner endorsing the product, so how can you blame the guy who went with an expert opinion? What's up with that? Doesn't Will Turner not know about this stuff either?

It is also interesting to see people finding the Dinan package expensive. Yes, it is pricy, but it actually seems to be engineered. I'd rather pay extra for proper product development, or not mod at all...

+1, I think its hilarious when people think that all you have to do to get the car to perform better is add some springs by H&R, tut really, if all it took was $350 springs, wouldn't BMW have done it? Seriously, why does everyone think an aftermarket mass market company knows more about how to make your //M perform better than BMW's M's division. Blows my mind......

[lucid]

Originally Posted by rldzhao

What do u mean underperforming?

Bumpstops are like springs, they absorb motion and convert them into potential energy when compressed, and then the potential energy is released when the spring/bumpstop extends.

Dampers DISSIPATE energy. They eliminate motion using the viscosity of the damper fluid.

Two totally different concepts...

Did you read my post? I clearly state that dampers dissipiate energy as you can see below.

Originally Posted by lucid

that means your dampers are not doing their job as designed, which is to dissappate energy.

See discussion here for more on the basics:

http://www.m3post.com/forums/showthread.php?t=146302

Now, what happens to suspension travel when it starts riding on the stops (regardless of the stops compressing and acting like a spring--they can do that in the stock setup as well so that's nothing new, but in the modified case you've now increased the combined spring ratio considerably from the very start)? What is the governing equation of a damper? (Or you can solve the differential equation for the sytems and look at the governing system equation). Put those together, and you'll see how the dampers stops functioning the way they are designed to function. Why do you think Dinan is trying hard to preserve travel?

[lucid]

Originally Posted by e46e92love

+1, I think its hilarious when people think that all you have to do to get the car to perform better is add some springs by H&R, But really, if all it tooks was $350 springs, wouldn't have BMW done it? Seriously, why does everyone think an aftermarket mass market company knows more about how to make your //M perform better than BMW's M's division. Blows my mind......

BMW picks the parameters of the suspension system for a general audience, who mainly drive on the street. If one is interested in a more aggressive setup, which won't be optimal for street driving, there is always room for imporvement. However, as you are saying, it is not as simple as dropping some aftermarket springs into the stock setup. If you change one parameter, the others are now out of line, and need to be re-considered and manipulated. Dinan is doing exactly that. Most folks don't get this though. Morever, certain parameters like suspension geometry are difficult to alter without making significant modifications.

[gthirtyfizle]

Basically, what ive gotten from all of this is, I need to buy some Dinan springs now. Great, there goes another grand. lol. But seriously, very good info here.

[rzm3]

First, I may have read your original post in a different way, and I appologize for that.

Originally Posted by lucid

Now, what happens to suspension travel when it starts riding on the stops (regardless of the stops compressing and acting like a spring--they can do that in the stock setup as well so that's nothing new, but in the modified case you've now increased the combined spring ratio considerably from the very start)? What is the governing equation of a damper? (Or you can solve the differential equation for the sytems and look at the governing system equation). Put those together, and you'll see how the dampers stops functioning the way they are designed to function. Why do you think Dinan is trying hard to preserve travel?

You are correct that the combined spring rate is higher than stock, but I don't agree that one can conclude that it is considerably higher. The bumpstop exerts force non-linearly, and the initial compression reaction forces are much lower than when it is fully compressed.

As with all lowering springs (Dinan, H&R, Eibach...), the spring rate is higher (because of shorter springs), therefore the damper will experience shorter travel and higher acceleration. Nonetheless, dampers are tuned to a range of values, not just rocket-science-like single value, so the entire system may still behave in a fashion that is similar to factory design.

Lets take a simple mass-dashpot system (the simplest suspension approximation) for example, the governing parameter is the damping ratio:



where c is the damping coefficient (assuming linear damper), k is the spring rate (assuming liner spring), and m is the mass. So with a higher k, the damping ratio would decrease, and here is a plot of systems with various damping ratios: (on y-axis is suspension travel, on x-axis is number of cycles in radians)



I am not an expert in auto suspensions, but I was taught in college that we usually want the system to be critically damped, e.g. damping ratio=1. So with a higher k, which means lower damping ratio, the system would become slightly underdamped. The problem here is that we don't know how much underdamped the system would become with an aftermarket spring.

We don't know what the values of c or k is, so even though k increases, the overall damping ratio may only be slightly affected. Therefore, what I am suggesting here is that real-life suspensions are very complicated non-linear systems, and without more technical details it is very hard to judge based on limited design specs.

The main point I want to make here is that we should not execute a manufacturer just because its competitor puts up an article that claims theirs is better. Which company doesn't claim that their product is superior?! Heck even Hyundai claims that their Genesis performs better than a BMW 550. But should we buy into Hyundai's claim just because of their commercials? Obviously not.

Dinan's approach may be the best and most comprehensive, or may be an overkill or some type justification for selling their products at a premium. H&R may have done a careless design job, or maybe they designed the springs with the bumpstop in mind. Two different approaches, and both may be acceptable.

I have absolutely no intention to start a Dinan vs. H&R fight here... I just hope that we, as car lovers, would consider the problem with a more comprehensive approach, not just based limited specs and claims. As I suggested in a different thread, the best way to tell is to have a side-by-side track run comparison: one stock M3, one with Dinan suspension, and one with H&R. Or if money isn't an issue, try both on your car

[doba_s]

How would H&R springs perform with the Dinan bump stops ?

[spyderco10]

Originally Posted by rldzhao

First, I may have read your original post in a different way, and I appologize for that.



You are correct that the combined spring rate is higher than stock, but I don't agree that one can conclude that it is considerably higher. The bumpstop exerts force non-linearly, and the initial compression reaction forces are much lower than when it is fully compressed.

As with all lowering springs (Dinan, H&R, Eibach...), the spring rate is higher (because of shorter springs), therefore the damper will experience shorter travel and higher acceleration. Nonetheless, dampers are tuned to a range of values, not just rocket-science-like single value, so the entire system may still behave in a fashion that is similar to factory design.

Lets take a simple mass-dashpot system (the simplest suspension approximation) for example, the governing parameter is the damping ratio:



where c is the damping coefficient (assuming linear damper), k is the spring rate (assuming liner spring), and m is the mass. So with a higher k, the damping ratio would decrease, and here is a plot of systems with various damping ratios: (on y-axis is suspension travel, on x-axis is number of cycles in radians)



I am not an expert in auto suspensions, but I was taught in college that we usually want the system to be critically damped, e.g. damping ratio=1. So with a higher k, which means lower damping ratio, the system would become slightly underdamped. The problem here is that we don't know how much underdamped the system would become with an aftermarket spring.

We don't know what the values of c or k is, so even though k increases, the overall damping ratio may only be slightly affected. Therefore, what I am suggesting here is that real-life suspensions are very complicated non-linear systems, and without more technical details it is very hard to judge based on limited design specs.

The main point I want to make here is that we should not execute a manufacturer just because its competitor puts up an article that claims theirs is better. Which company doesn't claim that their product is superior?! Heck even Hyundai claims that their Genesis performs better than a BMW 550. But should we buy into Hyundai's claim just because of their commercials? Obviously not.

Dinan's approach may be the best and most comprehensive, or may be an overkill or some type justification for selling their products at a premium. H&R may have done a careless design job, or maybe they designed the springs with the bumpstop in mind. Two different approaches, and both may be acceptable.

I have absolutely no intention to start a Dinan vs. H&R fight here... I just hope that we, as car lovers, would consider the problem with a more comprehensive approach, not just based limited specs and claims. As I suggested in a different thread, the best way to tell is to have a side-by-side track run comparison: one stock M3, one with Dinan suspension, and one with H&R. Or if money isn't an issue, try both on your car

I must have been sick the day they taught this in school!

[rzm3]

Originally Posted by spyderco10

I must have been sick the day they taught this in school!

I remember this because spring-mass-dashpot system is one of the most taught topics for a Mechanical Engineer: once in Differential Equations, once in Physics, once in System Dynamics, plus some other labs.

[Serious]

Real question is who is actually building these dinan springs?

because e36/e46 dinan suspension was pretty much off the shelf eibach springs and koni shocks, which charged twice as much for.

[rzm3]

Originally Posted by doba_s

How would H&R springs perform with the Dinan bump stops ?

Won't make a big difference: Dinan's is 2.125 inches, and I measured my stock bumpstop at 2.25 inches. Dinan's biggest difference is the -3 inch guide support.

So instead of riding 0.25 inches into the bumpstop, you'd be riding 0.125 inches into the bumpstop. (based on 1 inch h&r drop and 0.75 original travel before touching bumpstop).

[spyderco10]

Originally Posted by e46e92love

+1, I think its hilarious when people think that all you have to do to get the car to perform better is add some springs by H&R, But really, if all it tooks was $350 springs, wouldn't have BMW done it? Seriously, why does everyone think an aftermarket mass market company knows more about how to make your //M perform better than BMW's M's division. Blows my mind......

Most cars would actually handle better if the ride height is lowered. The lower center of gravity and decreased body roll = higher lateral acceleration. But the reason M, and other high performance divisions, will not make the stock ride height lower is because the car has to appeal to a broader audience than just extreme performance enthusiasts. A lowered car is impractical as a street car because it will scrape everywhere its driven and the ride will be stiffer, among other issues.

Anyone notice that the most expensive a sports car, which are engineered only for extreme enthusiasts, have very low ride heights?

Also M needs to controls costs, and high performance parts tends to cost $$$. Sure the M3 would perform better if they all came stock with Brembo BBKs. But it would be too expensive.

This theory also applies to many other parts of the car. Brakes, exhaust, wheel/tire combo, etc.

And I also think it's quite brave of some folk to criticize H&R, one of the world's most respected aftermarket spring manufacturer.

[ebohon]

I wouldn't mix and match parts... I will let someone else be the guinea pig. I was thinking along the same lines as RLDZHAO without the technical knowledge in terms of engineering by the various companies and how they choose to differentiate their products. I do appreciate Dinan taking the time to engage in this forum.

[lucid]

Originally Posted by rldzhao

You are correct that the combined spring rate is higher than stock, but I don't agree that one can conclude that it is considerably higher. The bumpstop exerts force non-linearly, and the initial compression reaction forces are much lower than when it is fully compressed.

As with all lowering springs (Dinan, H&R, Eibach...), the spring rate is higher (because of shorter springs), therefore the damper will experience shorter travel and higher acceleration. Nonetheless, dampers are tuned to a range of values, not just rocket-science-like single value, so the entire system may still behave in a fashion that is similar to factory design.

Lets take a simple mass-dashpot system (the simplest suspension approximation) for example, the governing parameter is the damping ratio:

where c is the damping coefficient (assuming linear damper), k is the spring rate (assuming liner spring), and m is the mass. So with a higher k, the damping ratio would decrease, and here is a plot of systems with various damping ratios: (on y-axis is suspension travel, on x-axis is number of cycles in radians)

I am not an expert in auto suspensions, but I was taught in college that we usually want the system to be critically damped, e.g. damping ratio=1. So with a higher k, which means lower damping ratio, the system would become slightly underdamped. The problem here is that we don't know how much underdamped the system would become with an aftermarket spring.

We don't know what the values of c or k is, so even though k increases, the overall damping ratio may only be slightly affected. Therefore, what I am suggesting here is that real-life suspensions are very complicated non-linear systems, and without more technical details it is very hard to judge based on limited design specs.

The main point I want to make here is that we should not execute a manufacturer just because its competitor puts up an article that claims theirs is better. Which company doesn't claim that their product is superior?! Heck even Hyundai claims that their Genesis performs better than a BMW 550. But should we buy into Hyundai's claim just because of their commercials? Obviously not.

Dinan's approach may be the best and most comprehensive, or may be an overkill or some type justification for selling their products at a premium. H&R may have done a careless design job, or maybe they designed the springs with the bumpstop in mind. Two different approaches, and both may be acceptable.

I have absolutely no intention to start a Dinan vs. H&R fight here... I just hope that we, as car lovers, would consider the problem with a more comprehensive approach, not just based limited specs and claims. As I suggested in a different thread, the best way to tell is to have a side-by-side track run comparison: one stock M3, one with Dinan suspension, and one with H&R. Or if money isn't an issue, try both on your car

If you read through that other thread I referenced, all of this has been discussed in some detail: the solution to the differential system equation, critical damping, etc. We also discussed the so-called robustness of the system in being able to function well with a range of k and c values as opposed to absolute specifications (and the code that controls damping coefficient in the active EDC modes). Even the automotive vs. aerospace example came up. Again, I suggest that you browse through that since there were several good points made by the contributors, and one of them was a controls expert (I'm not).

I disagree that we don't have enough information to have an opinion on if the combined spring rate will be significantly higher or not when the suspension is constantly riding on the stops. There are some basic design considerations that explain the stock configuration and how making the stock suspension constantly ride on the bump stops will increase the spring rate considerably.

As you know, when the suspension is riding on the stops, the coil spring and the stop act like two springs that are in parallel that are connected to the mass, so the effective spring rate is simply the sum of the two spring rates.

The suspension is not supposed to travel to the stop often to begin with. If the suspension was going to make contact with and compress the stop frequently, or constantly for that matter, and if the stop had relatively small stiffness, then they would have simply made the coil spring stiffer by that much or increased travel depending on the desired displacement response. Why make this separate component called a “bump stop”? Why make a second spring? The point of the stop is basically to keep a collapsing suspension from delivering too much peak force to the chassis, which might upset the balance of the car and damage structural components. The bump stop really becomes a last resort, and it makes sense that the effective stiffness of the system would go up nonlinearly and dramatically after the suspension contacts the stop and begins to compress it. Again, keep in mind that the increasing stiffness of the stop is simply being compounded with the stiffness of the coil spring. The increase in stiffness with initial stop compression might be low, but it can't be that way for long. If it could, then BMW would have simply designed that progressively increasing and relatively small stiffness into the coil spring. The bump stop will promptly deliver significant increased stiffness; again, this is pretty much by definition or it wouldn't be needed. I bet that when it is well compressed, the bump stop actually is stiffer than the coil spring (I've seen data on other car suspension bump stops demonstrating exactly that. If the M3 bump stop is not expensive, I am willing to take and post displacement vs. force data on it).

The track/real world “comparisons” have actually been run in a sense for many years. I’ve read many articles that qualify Dinan’s suspension products as the outcome of a comprehensive engineering approach, where the designers take their time understanding the issues and making—sometimes costly—modifications that are required as opposed to dropping in inexpensive individual components. The performance of Dinan suspension modifications are often praised in that regard. I’ve also read many first hand reports of cheap suspension mods going bad such as the example Gearheads provided. Yes, a controlled experiment run by a neutral party would be great, but we are unlikely to get it. Also, just because a company is trying to do the right thing doesn’t mean that they will necessarily do it right (just to demonstrate that I have no personal connection with or bias toward Dinan).

P.S. As a side note, shorter coil springs do not necessarily mean higher spring rates by the way. You can make a coil spring shorter and maintain its stiffness if you want by manipulating its diameter, materials, etc.

[lucid]

Originally Posted by spyderco10

But the reason M, and other high performance divisions, will not make the stock ride height lower is because the car has to appeal to a broader audience than just extreme performance enthusiasts. A lowered car is impractical as a street car because it will scrape everywhere its driven and the ride will be stiffer, among other issues.

That's not exactly the reason. The 335 coupe chassis rides 1"-1.5" lower than the M3 chassis depending on where you measure (also discussed in that thread I referenced earlier). However, there may be one exception, the differential cooling fins. They really stick out on the M3. There may also be flow issues. I am very curious about finding out why the M3 rides higher than the 335, but have not been able to do so.

Originally Posted by spyderco10

And I also think it's quite brave of some folk to criticize H&R, one of the world's most respected aftermarket spring manufacturer.

That's probably the problem actually. How many cars do they make springs for? I don't have the exact number, but it must be a lot. Understanding the details of how a specific suspension works and designing a custom solution for will take considerable time, money, and other resources. If it takes BMW years to develop and tune the behaviour of the systems, it must take others considerable time to understand it. Although I don't know the details of the aftermarket spring market (demand, margins, etc.), I don't see how an aftermarket spring manufacturer can do that if they sell their product for ~$300.

[rzm3]

Originally Posted by lucid

The suspension is not supposed to travel to the stop often to begin with. If the suspension was going to make contact with and compress the stop frequently, or constantly for that matter, and if the stop had relatively small stiffness, then they would have simply made the coil spring stiffer by that much or increased travel depending on the desired displacement response. Why make this separate component called a “bump stop”? Why make a second spring? The point of the stop is basically to keep a collapsing suspension from delivering too much peak force to the chassis, which might upset the balance of the car and damage structural components. The bump stop really becomes a last resort, and it makes sense that the effective stiffness of the system would go up nonlinearly and dramatically after the suspension contacts the stop and begins to compress it. Again, keep in mind that the increasing stiffness of the stop is simply being compounded with the stiffness of the coil spring.

The modern day bumpstops are not bumpstops in the old days; they are not hard, stiff rubbers to prevent metal-to-metal collision; they are not the "last resort." Modern day bumpstops are engineered elastomers, they act as supplemental springs, because elastomers can provide non-linear properties that cannot be easily replicated in coil springs. The reason why these engineered elastomers exist is because they provide a progressive suspension, allowing a smooth transition to full compression, with minimal weight and cost addition.

The M3 suspension, in stock form, has a compression travel of more than 3.5", which means that 3" of the compression travel is on the bumpstop, which means that the bumpstop is an integral part of the suspension system.

Originally Posted by lucid

P.S. As a side note, shorter coil springs do not necessarily mean higher spring rates by the way. You can make a coil spring shorter and maintain its stiffness if you want by manipulating its diameter, materials, etc.

A properly engineered shorter coil spring WILL be stiffer. One of the design considerations is that at full compression, the same amount reaction force should be provided by the spring. As you know, Fspring=kx (assuming linear), so in order to provide the same 'F' with a lower 'x', 'k', the spring rate, HAS to increase.

[rzm3]

Originally Posted by lucid

That's probably the problem actually. How many cars do they make springs for? I don't have the exact number, but it must be a lot.

This is not a good argument. With your logic, I can similarly say that H&R is a dedicated suspension company, while Dinan makes many other components: engine mods, exhausts, brakes, suspensions, wheels, and heck, even floor mats... you can see where I am going with your logic.

Again, I respect both companies. At this point I just don't know whose suspension is better performance-wise, and I would love to see some actual driving comparison.

Lucid, since you seem to believe that Dinan's system is superior, would you be interested in purchasing and installing the system? I live in NY, so we can meet and have a comparison.

[lucid]

Originally Posted by rldzhao

The modern day bumpstops are not bumpstops in the old days; they are not hard, stiff rubbers to prevent metal-to-metal collision; they are not the "last resort." Modern day bumpstops are engineered elastomers, they act as supplemental springs, because elastomers can provide non-linear properties that cannot be easily replicated in coil springs. The reason why these engineered elastomers exist is because they provide a progressive suspension, allowing a smooth transition to full compression, with minimal weight and cost addition.

The M3 suspension, in stock form, has a compression travel of more than 3.5", which means that 3" of the compression travel is on the bumpstop, which means that the bumpstop is an integral part of the suspension system.

The specifics of how much compression the stop will experience during operation is irrelevant. The point is that you will climb up the non-linear comression vs force diagram of the bump stop faster in the modified setup with reduced suspension travel. And, as I've said earlier, you'll run into the real steep part much more often. That steep part is the last resort. Therefore, you will experience a severe increase in stiffness more often, which is what you were saying that we could not conclude, and I am saying that we can because of what I've just said above.

Originally Posted by rldzhao

A properly engineered shorter coil spring WILL be stiffer. One of the design considerations is that at full compression, the same amount reaction force should be provided by the spring. As you know, Fspring=kx (assuming linear), so in order to provide the same 'F' with a lower 'x', 'k', the spring rate, HAS to increase.

I am not referring to the application of the spring; what you do with it. I am just factually saying it is possible to make a spring that is shorter and yet has the same spring ratio. That is a fact.

[EvilTuna7]

Originally Posted by rldzhao

What do u mean underperforming?

Bumpstops are like springs, they absorb motion and convert them into potential energy when compressed, and then the potential energy is released when the spring/bumpstop extends.

Dampers DISSIPATE energy. They eliminate motion using the viscosity of the damper fluid.

Two totally different concepts...

While you're correct in describing what each part does, the dampers were not designed to be used solely in conjunction with the bump stops. The dampers were valved to be used with the spring rates the springs provide. The bump stops are really just there to protect the dampers. So riding on the bump stops is most certainly going to cause a loss in suspension performance.

[lucid]

Originally Posted by rldzhao

This is not a good argument. With your logic, I can similarly say that H&R is a dedicated suspension company, while Dinan makes many other components: engine mods, exhausts, brakes, suspensions, wheels, and heck, even floor mats... you can see where I am going with your logic.

You are quoting selectively. I made a disclaimer saying I don't know the details of the aftermarket spring market. Also, note my use of the phrase "probably", which means I am just guessing on this one.

Originally Posted by rldzhao

Lucid, since you seem to believe that Dinan's system is superior, would you be interested in purchasing and installing the system? I live in NY, so we can meet and have a comparison.

If I do end up going for the Dinan setup, and you end up going for the H&R setup, I'd be happy to meet and exchange cars for a comparitive experience. I don't do street racing if that's what you mean though.

[rzm3]

Originally Posted by lucid

I am not referring to the application of the spring; what you do with it. I am just factually saying it is possible to make a spring that is shorter and yet has the same spring ratio. That is a fact.

Yeah of course, if you cut a spring in half, both halves will have the same k. But I was talking specifically about lowering springs in my original post.

Correction: first sentense is incorrect.

[rzm3]

Originally Posted by EvilTuna7

While you're correct in describing what each part does, the dampers were not designed to be used solely in conjunction with the bump stops. The dampers were valved to be used with the spring rates the springs provide. The bump stops are really just there to protect the dampers. So riding on the bump stops is most certainly going to cause a loss in suspension performance.

You are correct. Dampers are valved to be used for the overall spring stiffness of a system. I never said otherwise.