Coilover Theory 101: Coil Spring Comparison

[YCW]

Originally Posted by Bonburner

Thanks for sharing this information .. but it really wasn't coilover theory 101 ...
was more like brand vs generic 101.


Typically brands are held to a higher in-house standard than generics and we see this in your sample size of 1 test. ¯\_(ツ)_/¯

The reason for the title "Coilover 101" is because I'm planning on doing other parts to the series, such as manufacturing, valving theory etc; it's not just about coil spring testing. And when testing coil springs, it has to be either Brand vs Brand (which is coming) or Brand vs Generic. There is no other way to do a comparison otherwise

[Ultramaroon]

What are the reaction forces at full compression. Are both springs linear?

[YCW]

Originally Posted by Ultramaroon

What are the reaction forces at full compression. Are both springs linear?

The Intercomp spring rate tester is based on "distance", so to be accurate, I chose to set this to 1 inch (for obvious reasons)


For reaction forces, only a dyno can show this, like the Roehrig dyno graph I posted above for the 100lbs/in sample spring.


Yes, both springs are linear.

[Ultramaroon]

Originally Posted by YCW

The Intercomp spring rate tester is based on "distance", so to be accurate, I chose to set this to 1 inch (for obvious reasons)


For reaction forces, only a dyno can show this, like the Roehrig dyno graph I posted above for the 100lbs/in sample spring.


Yes, both springs are linear.

What? You don't need a dyno for static forces. Dynos are for motion profiles - reaction forces as a function of speed.


Why not take some data? 1.5, 2, 2.5 ...

[YCW]

Isn't that what you were asking for? Reaction forces over the full range of compression?


If not, then I misunderstood and apologise.


If it's just static forces you require based on "distance", then yes, we can do that, not an issue.

[Ultramaroon]

Originally Posted by YCW

Isn't that what you were asking for? Reaction forces over the full range of compression?


If not, then I misunderstood and apologise.


If it's just static forces you require based on "distance", then yes, we can do that, not an issue.

Yes, I wonder why, if one manufacturer can get away with using less material, then why don't all do it? What are the trade-offs? Serious questions.

[YCW]

Originally Posted by Ultramaroon

Yes, I wonder why, if one manufacturer can get away with using less material, then why don't all do it? What are the trade-offs? Serious questions.

Swift get away with it because they changed the metallurgy of their steel, rather than sticking with the common-place SAE 9254 or 9254V, so their steel can hold more compressive forces compared to the same weight of steel used by another brand.


I am going to try testing a Titanium spring as well, but due to the cost of them, not as easy to get hold of.



What determines the rate is the overall mass of steel, not how many coils there are (according to the Swift technician). Obviously on a linear spring, the coils need to be evenly spaced (regardless whether they are straight or barrel).

[Ultramaroon]

Originally Posted by YCW

What determines the rate is the overall mass of steel, not how many coils there are (according to the Swift technician). Obviously on a linear spring, the coils need to be evenly spaced (regardless whether they are straight or barrel).

I'm pretty sure it has nothing to do with the material's mass and a lot to do with its shear modulus. Given equal spring displacement, more coils result in less strain per unit length of wire.

This means the wire in the swift spring has to twist more than the generic spring for a given displacement.

I'm not expert in this application but in general, less turns must be paired with thinner/weaker wire to get the same spring constant. At some point it impacts lifespan of the spring.

[YCW]

Originally Posted by Ultramaroon

I'm pretty sure it has nothing to do with the material's mass and a lot to do with its shear modulus. Given equal spring displacement, more coils result in less strain per unit length of wire.

This means the wire in the swift spring has to twist more than the generic spring for a given displacement.

I'm not expert in this application but in general, less turns must be paired with thinner/weaker wire to get the same spring constant. At some point it impacts lifespan of the spring.

I'm not an expert in the manufacturing/design of springs neither, so this is something that I would need to look into further. As mentioned though, it was just something that the Swift technician briefly explained to me during our last meeting. If I recall correctly, he basically said a 10K spring will always have the same overall mass, regardless of length. I will clarify with him again.


Regarding "Given equal spring displacement, more coils result in less strain per unit length of wire.", that is correct, however, you also need to factor in the material used. Not all springs are made from the same material, hence the differences between Swift/Hyperco/Eibach/Taiwan etc


I will run some tests on used/older springs and see what results come up.

[Spuds]

Originally Posted by Ultramaroon

I'm pretty sure it has nothing to do with the material's mass and a lot to do with its shear modulus. Given equal spring displacement, more coils result in less strain per unit length of wire.

This means the wire in the swift spring has to twist more than the generic spring for a given displacement.

I'm not expert in this application but in general, less turns must be paired with thinner/weaker wire to get the same spring constant. At some point it impacts lifespan of the spring.

Well, as long as the stress on the spring doesn't exceed the fatigue limit of the material, it should last damn near forever right? I think that's where a brand name spring's metallurgy and higher detail of engineering come in. My guess is that they also probably have a lower factor of safety because there is more control over the manufacturing process.

I went to school for aero, so my materials science education is a bit basic, so I may be missing something.

Also, I'm very proud of myself for engaging in technical discussion without using acronyms.

[Ultramaroon]

Originally Posted by Spuds

Well, as long as the stress on the spring doesn't exceed the fatigue limit of the material, it should last damn near forever right? I think that's where a brand name spring's metallurgy and higher detail of engineering come in. My guess is that they also probably have a lower factor of safety because there is more control over the manufacturing process.

I went to school for aero, so my materials science education is a bit basic, so I may be missing something.

Also, I'm very proud of myself for engaging in technical discussion without using acronyms.

Nope. I don't think you're missing anything. If the assumptions about control of manufacturing process hold true, it all makes sense.

[Spuds]

Originally Posted by Ultramaroon

Nope. I don't think you're missing anything. If the assumptions about control of manufacturing process hold true, it all makes sense.

And that's the big IF right? What we really need would be a higher sample size as mentioned before. But that gets expensive pretty quick if you want to be really science-y about it.

Also, what parameters should we really be looking for to determine manufacturing quality other than spring rate?

[YCW]

Originally Posted by Spuds

And that's the big IF right? What we really need would be a higher sample size as mentioned before. But that gets expensive pretty quick if you want to be really science-y about it.

Also, what parameters should we really be looking for to determine manufacturing quality other than spring rate?

I have thousands of springs on the shelf, albeit all Swift, so not sure if that would provide a fair set of data or not though. I'm limited with regards to "new" springs from other brands, but for the used ones that we do get in, I have no problem putting them on the tester


With regards to parameters, besides spring rate, probably consistency/sag over a period of time (that's where testing used springs comes in useful) e.g What length is your 180mm spring after say 6 months of consistent use


If aesthetics is included, then the type/quality of the paint I guess.

[Captain Snooze]

Would I be able to tell the difference between the Swifts and the generics? 0.25k doesn't read significant to me.


Why isn't there a rod going through the axis of the spring in the spring tester or a cage around the spring. Do springs never pop out?