When the wire is thin for a soft rate, and the ID of the wound linear spring is small, the spring trying to move off axis IS the material trying to avoid plastic deformation. The fact it is forced (by rubbing on the shock body) to stay close to on axis DOES weaken the material the spring is comprised of.

Because its elastic range is greater than a brittle material (like Delrin i mentioned earlier), it will continue to take the abuse until... like you said... it fails and breaks. (When has ANYONE seen an AE spring fail like this?) Delrin fails far earlier.

This is why i say a larger ID spring works more efficiently at supporting the SAME load at the same rate. This is why i say the feel ISNT progressive, but the nature of the material being able to do its job within its plastic limit. Soft rates require more material to effectively support the same load regardless of coil quantity... but this does not increase rate.

At some point coil quantity could be excessive, and you would be back to the spring failing to do its job efficiently, so you would have to widen spring ID to maintain the same rate...

1) Not exactly, if you make the wire diameter thinner, then you have decreased the spring rate. Then if you also make the diameter larger, then you will have further decreased the spring rate for a given number of coils. If by "staying on axis" you are refering to buckling, then the wire diameter does not effect this. But the increase in coil diameter does reduce its tendancy to buckle, since the buckling calculation is a function of the spring free length divided by the coil diameter. If this number is greater than 4 then it is safe to say that it will not buckle during its travel. If this ratio is less than 4 then it will have a tendancy to buckle, and given two springs of equal free length and coil diameter, the one with a higher spring rate will buckle with even greater force making it even harder to collapse axially.

2) Yes, having a good spring manufacturer is very important because a spring can obviously be designed for an exact spring rate, yet manufacturing tolerances will make that difficult to achieve consistantly, especially since some of the parameters can be so sensitive!

3) I think that it is tougher to get the same tolerances on a more slender spring that has a smaller wire diameter, especially when it is close in number of coils to a big bore spring for a couple of reasons.
1) The total length of wire on the slender spring is less! This then makes all of the other geometric parameters of the spring even more important that they have good tolerances because you have less material that you are working with that needs to absorb the same energy.
2) Given a certain diameter tolerance that a spring manufacturer can achieve say .05". Now lets say you have two springs, and one has a larger diameter (say .5" and .625"). The spring with the smaller diameter will be more greatly influenced by this .05" tolerance because it is a greater percentage of the diameter and results in a greater variance in spring rate (10% for .5" and 8% for .625, in this case)
3) The number of coils is another and the toleranceson that .
A couple other factors might be how straight the spring is wound, the length, and powder coating.

All these factors are what introduce all of this spring rate inconsistancy. I think a BB spring is inherently better because it does have more wire length for an equivalent spring rate as well as a larger diameter wire, and this helps reduce the stress in the spring when compresed and overall is just better spring design. I am sure they guys at AE have done their math right, there are a lot of pretty sharp guys over there with lots of experience. But it ultimately comes down to the manufacturers tolerances and cost. Kyosho is able to get very fine spring increments with minimal tolerance overlap and variance...but you pay for it!

Yes, in this example 2lb/in IS the rate. This is the constant and does not change. This is regulated by wire size and material composition.

If this were a simple math problem i would say:

"Give me several different formulas to derive a constant X, in this case 10."

Simplex answers could be:

"5x2=10"
"5+5=10"
"20-10=10"

Just as 10 is the constant here, 2lb/in is an unchanging constant...

Yikes! Snuck in a lot of replies on me!

The diff springs are a very special case because their spring rates are soo high! And they must be in such a small area, and I think this is just to give the spring an initial 'set' before you install it since it has not been compressed before that. This may also be just to make it easier to thread the diff nut.

Most compression springs (for shocks atleast) are designed way under the elastice limit, so they are never even close to the elastic limit. But I agree a smaller coil diameter will result in less stability, or I guess as you have been calling it "efficiency" given the same free length.

Cool, I'm a mechanical engineer as well!

Its late and im tired as all hell, but if powdercoating a spring that small introduces that much variance... why is it done???

Yes it can be called buckling... its the material trying to avoid plastic deformation.

By saying, "The thinner the wire size, the larger the ID of a linear compression spring should be, for it to be able to do its job effectively and stay on axis."... i wasnt saying thinner wire wouldnt change the rate... i was saying a thinner wire would need a larger ID to stay on axis and avoid said 'buckling'.

That is hard to do though (costly) because a kit would have to include larger upper and lower spring perches for larger softer springs, and smaller upper and lower spring perches for the stiffer springs (at a certain point). I guess this would also depend on a chassis 'sweet spot' and tunability... but thats a different ball of wax...

Yeah sorry... doing 5 things at once, and spinning back round to the PC when a thought hits me... lol

To give you an idea of my anality (and i hate mech school for this), i used to make sure all diff springs were compressed and then sized (i ground them) equally so i could install a spring and know how far to back it off for the same setting AFTER breakin. That way i didnt have to make that extra readjustment step. Just drop it down and go...

Im not a practicing engineer though.

I found out i hate desk jobs. I enjoyed it more when i was at a drawing board, and not a computer screen. Gimme 4h, construction lines, and a gum eraser and im happy...

i'll bet my left nut that associated is learning a lot from this. who would of thought that having a spring made and powder coated could spark a whole discussion on it. lol

Awesome thread, way back in the day, say JRX-Pro times some guys used to remove the coatings, one guy said he could feel the difference LOL. I always thought it was a mind game...

Anyway, glad to see someone with the credentials posting to dispel all of the misinformation about springs.

Great read, thanks for the info! I'm going to link to this thread in the tune with camber links thread.

subscribed!

A spring stores and releases energy. Anything that can be rated for energy use/release can be rated for efficiency.

In this hobby were more familar with efficiency when in reference to batteries and motors than anything else... but again as a general rule the same parameters can be applied.

Design parameters and cost usually limit the true potential of any project... especially if its intent is mass production. Because of this i truly doubt a large amount of RnD goes into spring design for RC cars.

I can see it being of greater importance for companies like Serpent/XRay/etc... that pride themselves in 'over engineering' their designs. Their products are often prime choice for fitment on other so called inferior designs. Like you said before, you pay for the Kyosho product.

This entire discussion was started over "progressive spring rates" and this pic was provided at the start of the discussion....



As i stated before, (and i should have included the word static, which i believe you call 'free length'?), a spring rate cannot be progressive unless its wire size is changed. The above pic shows what a true progressive rate spring looks like.

Despite efficiency, plastic deformation, simple math, or complex equations, our offroad linear springs are NOT progressive in nature. They arent designed as such.

bump to the front for reminder

This may be a progressive spring... but not the only type that is. I do not subscribe to the theory that the wire diameter has to change to be progressive. By the admission of the two Mech. engineers on this thread alone (and my personal experience and knowledge) if you add to the coils in a section of similar wire diameter spring the rate in that section goes down... so it is safe to say in my estimation that any spring wound with one or both ends wound with more coils will be softer in those sections. It can make them either progressive or staged depending on how the coils are arranged. I agree that 99% of all of the springs I have seen for RC cars are straight rate FWIW. I have seen progressive springs... but I don't know if they would help or hurt suspension tuning (usually I have only seen them on Traxxas type of vehicles).