Also, "G" doesn't change much for a material. As far as stiffness is concerned, steel is basically steel. But spring steel has a higher yield stress, so it can be twisted further, or made thinner, and still withstand the cyclic loading. When designing a spring, "k" is your output, it's what you are designing to. "D" is also fixed, because the certain spring has to fit on a certain coilover (it'll change very slightly because inner diameter is what is held constant, and "D" will grow as wire diameter grows, but it's negligible for this level of thinking). You are left with 2 variables, you are basically playing with the ratio of wire diameter to number of active coils. If you make these both smaller at a certain ratio (note that wire diameter is taken to a power of 4 so it has a lot more influence), the spring rate will stay the same, the weight will go down, and the compressed spring length will be shorter (so less likely to coil bind). The downside is that stress goes up. So lighter smaller springs (like the Swift) need to be made out of higher quality material, have better tolerance control, and have more testing to prove which load cases it's safe to operate in. Improving that quality also leads to more consistent spring rates.

 

But but but but you titled the thread "Theory 101"
(and you're a vendor... so it's ok to advertise)

We have a winner.

 

Yeah, I know. My original intention (and still is) was to gather data, share it with the community, and together we can analyse that data to come to whatever conclusion(s) on the various brands of springs. On top of that, those with the engineering knowledge (I have zero experience on the spring metallurgic properties side of things. Yes, I sell them, but if things get technical, I still need to ask Swift. I'm not ashamed to admit that) can share their knowledge and we can all learn from it (I certainly have). The "Theory 101" threads is my idea of putting all this "community research" into an easily accessible thread, instead of have to search all over the place.

Unfortunately, being a vendor at the same time, some may find this as "advertising in disguise" (as I just found out on the other forum). This thread is not brand-specific, and if the community decides to name-and-shame a brand based on the data/results (even if it's Swift), that's fine.

 

Nah, we won't let that happen. This will stay productive and educate the n00b masses. MT is the last frontier for this type of stuff. The "other" place has been a joke for the past 10 years.

 

^ This.

Some folks will undoubtedly criticize you, your data, your research methodology, your conclusions, your sexual orientation, etc.

We will deal with them as they occur. Those which are sufficiently humorous will be allowed to slip through, those which are not will be filtered out, and if history is any indication, Pusha and/or Faeflora will wind up getting banned yet again.

 

I was one of the haters, but if you want to convince people on here, then data is definitely a good start.

 

I have been wondering one thing but haven't really looked into it and you seem like you may know. Does the force exerted by the spring actually increase linearly as their lo ratings would suggest? Note, I'm a civil engineer so I have decent understanding of static loads but a **** poor understanding of loads in things once they start moving. I would imagine spring steel has a linear stress strain curve up to yield stress (which is hopefully not practically achievable in spring steel) but I don't know how much shape would effect the load rating. I know their is an equation for spring rate on the previous page but is that based on material properties or empirical and only relevant to part of the springs motion?

 

I'm not a suspension guru, however I'm fairly certain that the rate of most aftermarket automotive suspension springs is linear across their range of travel.

Eg: if it takes 400 lbs to compress the spring by 1", it will take another 400 lbs to compress it by 2", and another 400 lbs to compress it by 3", and so on until some limiting factor is reached.

Some springs are made non-linear by spacing the coils more closely at one end than the other. In such a design, as the more tightly-spaced coils start to bind, the effective length of the spring decreases, and its rate increases.

 

^ Listen to Joe. He's an uncivil engineer.

 

Just to nit pick, the number of active coils decreases when coils bind (see formula on last page), length actually doesn't matter.

 

These two concepts are functionally interchangeable.

To be *super* nit-picky, the overall length of the spring (the total length of the metal rod, as though it were un-coiled from spring form, and which exists unbound in free space) is what matters, assuming thickness, hardness, metallurgical composition, etc., to be a constant.

For such a piece of metal which is formed into the shape of a coil-spring, "number of active coils" and "effective spring length" vary according to the same parameters, and mean the same thing.

Also, I'm a bit drunk right now, and it's been more than a day since I've banned anyone, so I'm feeling itchy in that regard.

 

Couldn't fine the cheers smiley, so that will have to do. Yeah, I was thinking you meant coiled length!

 

Yeah, if you take a look at the image of the dyno graph of the 100lb spring sample, you will see that as the force increases (the x-axis), the spring rate (the y-axis) remains constant. This is what you want in a linear spring.

I'll try to have more dyno graphs posted up (of other brands as well) within the next week or so.