spring rate and ppi? same thing?

[gwaii]

I would agree, however it seems that no one really reads the stickied threads.

isn't this the truth!

when explaining spring rates,i find that most people get the basic lbs/inch concept,and can usually get the idea of base compression (the difference between full droop and ride height)through-though on this one i like to figure in an inch or two of full droop preload so the spring never becomes fully unloaded-but what most don't seem to get is the leverage effect of the ttb arm(or any suspension arm that is pivoted off the frame and carries the spring,for that matter).it was good to see that specified.
there is one thing to add for those who want to get picky-the main beam does not act as a single piece in this system.it is actually working with the radius arm as a single large swing arm assembly,so to calculate spring leverage you need to draw a line through the two pivots in the system(beam pivot/radius arm pivot)and strike a line perpendicular to this hinge line that goes through the tires contact point on the ground.the distance between the pivot line and the tire that the spring sits at is the ratio you use to calculate spring rate.
by playing with the numbers you can see how extended radius arms can affect the effective spring rate.
longer radius arms stiffen the spring rate.

 

[4x4junkie]

isn't this the truth!

when explaining spring rates,i find that most people get the basic lbs/inch concept,and can usually get the idea of base compression (the difference between full droop and ride height)through-though on this one i like to figure in an inch or two of full droop preload so the spring never becomes fully unloaded-but what most don't seem to get is the leverage effect of the ttb arm(or any suspension arm that is pivoted off the frame and carries the spring,for that matter).it was good to see that specified.
there is one thing to add for those who want to get picky-the main beam does not act as a single piece in this system.it is actually working with the radius arm as a single large swing arm assembly,so to calculate spring leverage you need to draw a line through the two pivots in the system(beam pivot/radius arm pivot)and strike a line perpendicular to this hinge line that goes through the tires contact point on the ground.the distance between the pivot line and the tire that the spring sits at is the ratio you use to calculate spring rate.
by playing with the numbers you can see how extended radius arms can affect the effective spring rate.
longer radius arms stiffen the spring rate.

Exactly.
http://img.photobucket.com/albums/v173/sfr4x4/ttbsymetry.jpg

The 1.5:1 figure is always pretty close though, and seems to work for most people.

I probably have a PM from you saved in my inbox that says basically exactly what I typed.

Wondering how old that PM is

 

[spdcrazy]

makes perfect sense! i'm using skyjacker arms now, however i'm not happy so i'll be building my own soon!

my local spring shop is working on finding some coils now. and measuring them for me. i'll look into what exactly i need for spring rate, and length and stuff this weekend.

 

[Sasquatch_Ryda]

Wondering how old that PM is

I have one of those too

 

[spdcrazy]

hey guys. my local spring shop has a machine that compresses a spring and tells you how my PSI it takes to move it. Is there any way to caculate this into PPI? or how can i use this psi measurement in calculating what i need? I was thinking about making new coil buckets top and bottom and adjusting their locations to help fit a different spring. They have plenty of different length springs laying around, so if i can find one that fits my numbers ( still working on, free length could be 21 as the stock buckets sit), i'd like to see what i can do.

 

[4x4junkie]

Shouldn't be any calculating needed. Once the machine has compressed the spring exactly one inch, whatever force it took to do so is your PPI (as Bray D mentioned earlier in the thread, PPI = Pounds Per Inch). If the machine doesn't have a readout in pounds of force for whatever reason, then I couldn't help you, you'd have to consult the machine's manual (or the guy running it).

 

[gwaii]

if you know the diameter of the piston in the ram,it's easy to figure out total force.

take half the diameter,multiply that by itself,then multiply the answer by 3.14.take the resulting number and multiply the pressure reading by it.
this is total force on the spring.compress the spring a few inches,then divide the force by how many inches you compressed the spring(one inch compression won't give as accurate a reading as more compression)

as an example...say the piston is 4" diameter,half that is 2.multiply by itself,2x2=4.
multiply this by 3.14.......4x3.14=12.56.

now say the reading on the pressure is 200lbs-multiply this by 12.56.

200x12.56=2512.now,say you compressed the spring 10",the rate is 2512/10=251.

so your spring rate is 251lb/in.




edit-the ram is the part that moves out of the cylinder,it should be easy to measure.

 

[bobbywalter]

i run 140-60 springs with airbags at one point.

best compromise....tune on the fly for good road manners and awesome on the trail.


but you have to customize the buckets or lower seats to mitigate the coil bow.

 

[Bray D]

edit-the ram is the part that moves out of the cylinder,it should be easy to measure.

The size of the piston (that the pressure acts on) doesn't necessarily have the same area as the rod (ram). You need to know the ID of the cylinder, which would be a bit harder to measure.

 

[gwaii]

not always,especially on general purpose rams,but on press rams they usually are.they want to make them as big as possible to take up side loads and give end surface area..

 

[JohnnyU]

This machine probably uses a bottlejack. Bottlejack pistons are typically just a solid piston, with seal grooves machined into the last inch or so. Pressure is durectly applied to the end of the rod (piston). As gwaii said, this is done to maximize the piston area while minimizing the need for lateral support. Also, since it is single-asting, there is no need for a working suface onteh opposite end, gravity and the load typically force the piston back into the cylinder.

 

[gwaii]

This machine probably uses a bottlejack. Bottlejack pistons are typically just a solid piston, with seal grooves machined into the last inch or so. Pressure is durectly applied to the end of the rod (piston). As gwaii said, this is done to maximize the piston area while minimizing the need for lateral support. Also, since it is single-asting, there is no need for a working suface onteh opposite end, gravity and the load typically force the piston back into the cylinder.

those with bottle jacks are this way,but the big industrial machines are like this too(though the cylinder is generally inverted so the ram exits the bottom)on these some are multi-stage machines where the central piston is surrounded by cylindrical piston "extensions" that increase the working diameter of the piston-the middle stage is fast acting,but lower force,as subsequent stages come into play the speed goes down,but the force goes up.in this case you need to measure the stage that is actually working on the spring.

 

[spdcrazy]

hmm. good info. i'll stop by the spring shop. and see how their machine is built. im getting frusterated trying to find some springs locally. I don't mind rebuilding my coil buckets at all. in fact i look forward to putting my new welding skills to the task. but i still need a spring to start with!!!