Pirate 4x4 banner

1 - 10 of 10 Posts

·
Premium Member
Joined
·
387 Posts
Discussion Starter #1
This might be a long shot, but I was just wondering if anyone (Engineer or not) knows the spring constant "k" (as in F=kx)for a stock YJ spring pack assembly. Front or rear or both is fine.
Also, I need the damper constant "b" (as in F=bv)for a Rancho 9000 on any of its five settings.
 

·
Registered
Joined
·
203 Posts
I think this is what you are looking for and if not forgot what I wrote.

29,900,000=K
 

·
Registered
Joined
·
523 Posts
Originally posted by Cochese:
<STRONG>This might be a long shot, but I was just wondering if anyone (Engineer or not) knows the spring constant "k" (as in F=kx)for a stock YJ spring pack assembly. Front or rear or both is fine.
Also, I need the damper constant "b" (as in F=bv)for a Rancho 9000 on any of its five settings.</STRONG>
It might not be real accurate, but you could calcualte it by putting a measured amount of weight on your front or rear bumper, and measure the squat, then divide by two since you got two springs supporting the weight. Since the weight isn't directly over the axle, there will be some error. Also, I doubt a leaf spring really has a constant spring rate, it probably varies with the amount of arch, with it's lowest value when the spring is flat, but that's just a guess.

In theory you could also calcualte the damping rate of a shock with empirical data, I don't know that one off the top of my head

chad
 

·
Registered
Joined
·
288 Posts
hey eric, there is an SAE handbook in the RBD library with the equation you are looking for. remind me bout it and ill show ya where it is.
 

·
Registered
Joined
·
318 Posts
Originally posted by KYJ:
<STRONG>It might not be real accurate, but you could calcualte it by putting a measured amount of weight on your front or rear bumper, and measure the squat, then divide by two since you got two springs supporting the weight. Since the weight isn't directly over the axle, there will be some error. Also, I doubt a leaf spring really has a constant spring rate, it probably varies with the amount of arch, with it's lowest value when the spring is flat, but that's just a guess.
</STRONG>
I agree with that. It might not be totally accurate but it's not like you're sending this thing to the moon.

Just take your F=kx => k=F/x. You know what f is from the weight you put on and you know what x is from your measuring tape. You might do this for several different weights. 20 (if this displaces the springs at all), 40, 60, 80. Or maybe a 150lb friend and a 200lb friend and a 250lb friend. Take the average. It may prove to be more accurate over the travel range assuming the spring rate is not constant.

29,900,000 newtons to displace a YJ spring 1 meter? Whew. I'll stay away from those then. <IMG SRC="smilies/smile.gif" border="0">

[ 10-18-2001: Message edited by: BigBadBob ]
 

·
Registered
Joined
·
2,540 Posts
The number Donovan gave you is the modulus of elasticity for steel. It is in units of lbs per square inch. it relates stress in units of PSI to strain in units of in/in in the elastic region. It is not exactly what you are looking for, although with that number, the dimensions of the leaves and the equations F=KX, X=FL^3/3EI, and I=1/12bh^3 you can calculate the spring rate. <IMG SRC="smilies/tongue.gif" border="0">

The damping of your shock is not that simple, actually the number you are looking for changes significantly with shaft speed.
 

·
Registered
Joined
·
221 Posts
In my experience YJ leafs are about a little shy of 100lb/in,,, a good referance for comparison of different trucks is a Rancho catalog, they list their spring rates. The problem though is that that guestimate of a spring rate is is just that, leaf springs tend to have variable rate.
damping constant is in units of force/speed, (FYI)... Dont know the rancho shock constants off hand, but dont forget, a lot of modern shocks are also variable damping rate.

If you dont mind, tell us what you are trying to do, maybe we can help,

In my experience, the theoretical engineering equations only work well when the right assumptions are made. And it is VERY difficult to make accurate assumptions about real world vehicles(ie: how friction in the spring bushings effects spring rate, and damping rate). They do work well, though on a slinky with a fishing weight on the end.
Just one man's opinion.
Good luck with the calculator.
 
1 - 10 of 10 Posts
Top