|07-05-2010 09:26 AM|
|THERACER||This is getting interesting for sure, great info here !!!!|
|07-05-2010 08:31 AM|
Rule of thumb the smoother the track the stiffer the spring..If the car is too stiff then it will "pogo" and get loose in the chatter boards or rough portions of the track. main thing to understand is that the spring rates and shock valving is a variable component in setting up the car..Of course we now have cars with computer contolled active suspensions that adjust on the fly to road conditions going from soft ride to stiff when excessive body lean or roll is detected. Back in the day we carried several sets of springs and used the rebuildable/revalvable shocks to try and find the happy spot for the particular car and driver on a particular track.
|07-05-2010 06:57 AM|
A couple more comments that come to mind:
Some of the autocross cars have wheel rates over 600 pounds per inch! The tire has a rate of approximately 1000 pounds per inch, so these cars are essentially oversized karts.
Before the ground effects cars were banned from Trans Am racing, it's my understanding that the constructors were considering simply doing away with the suspension springs.
We've all driven karts, at one time or another, and we didn't miss the suspension on a smooth kart track. But, driving or riding on city streets is another matter! I remember, back in the fifties, getting a ride into work with another Chrysler engineer. His car was an Elva http://www.elva.com/elva-history.html. Appreciated the way it handled, but my tailbone was glad to reach the parking lot!
|07-02-2010 01:14 PM|
Anyway, good luck and I will follow along w/interest.
|07-02-2010 01:13 PM|
You're talking a range which spans almost an order of magnitude. This is meaningless. If you want a vehicle which rides like a luxury car, you can't start with a beam front axle. The compromises I described resulted in the introduction of independent front and rear suspensions.
|07-02-2010 11:40 AM|
Cobalt, Teflon Liners
Mark, I may have the liners done with the new springs. The reading on Eaton's site is pretty interesting regarding the liners, slip pads, grease, etc.
For example, back in the day, I used to grease between the leaves or shoot oil in every crack and crevis to make my old '58 ride smooth and squeak free.
(along with concrete blocks in the bed) What I didn't know then, was the oil and grease will break down chrome carbon steel!
According to Eaton, you can tell if a big leaf spring truck has had a long term power steering leak by noticing a sagging front end on the same side as the power steering pump!
Do you remember when the trick of the week was disassembling the leaves, packing with grease, reassembling and wrapping with wide electrical tape to waterproof? Haa Nolan
|07-02-2010 11:19 AM|
Hats Off To Billy & Sam!
"I can find a hundred men to tell me an idea won't work. What I want are men who will make it work." Herbert Dow, founder of the Dow Chemical Co.
Hats off to ya'll, Now we're cooking with gas!
I'm starting to get a better feeling about this now, the input is giving me alot of food for thought.
The corner load/spring rate multiplier figures were very eye opening. If I'm understanding it correctly,from one end of the scale to the other for example on a 2000# front end, 1000# corner load would equate to a 26#-230# spring rate. The rear weight of 1365#/682# corner load would equate to a 18#-157# spring rate.
Based on weight, the middle of the sports car range would equate to 184# front and 126# rear spring rates. I think I'm getting it. So my spring choice is going to be more of an educated guess than a shot in the dark. Plus I can talk shop with the man at Eaton to see how he feels and what he can build for me.
Thanks by the tons for getting me started, its really hard to find folks who will take the time to discuss it.
This discussion may resume after I find out what Eaton can do.
Many Thanks, Nolan
|07-01-2010 06:18 PM|
This is probably all well known to you already, but in case someone else isn't aware, Eaton makes a material for using between the leaves, shown being used HERE:
Skyjacker makes teflon replacement leaf spring wear pads.
Along w/clean, smooth spring surfaces and smooth-acting spring mounts and/or shackles along w/the removal of a leaf should help to tame the ride some, if the OEM parts were going to be reused.
|07-01-2010 05:53 PM|
If this were mine and I had to turn this into something doable in the shop I would stick with the stock springs up front..remove some leaves in the rear to get me close to 125/150 in the rear..add the slide-a-links and some sway bars.
Once that is done we can now work on shock valving I have found that alot of issues with ride and handling are traceable to shock selection..
|07-01-2010 04:33 PM|
With a beam axle, both wheel rate and roll stiffness must be taken into account. When one wheel drops into a pothole, the situation is quite different from hitting a speed bump. The speed bump situation is akin to that which I referenced when I said the spring rate is equal to the wheel rate. Unless a hefty sway bar is used (which increases manufacturing cost), however, a compromise is necessary. This results in spring rates which cause you to lose your fillings when you hit a speed bump, but are otherwise acceptable when a pot hole is encountered. At the front of the car, steering requirements move the leafs close to the car's centerline, resulting in a greater compromise (and higher spring rates) than at the rear.
Since I hate trips to the dentist, I'd go to a lower rate at the front and sneak in a sway bar.
The following is a post from another thread:
A very popular reference book among suspension engineers is Race Car Vehicle Dynamics by William and Douglas Milliken. (It can be purchased through Amazon.)
On page 582, ride frequency ranges for different vehicle types are given. For a sports car, the range is from 70 to 90 cycles per minute. For a passenger car, 30 to 50 cycles per minute.
With an 800 pound corner weight, the 150 pound per inch wheel rate would put you right in the middle of the sports car range.
For greater convenience, the ranges can be expressed as a multiplier, which, when multiplied by the corner weight, gives you the wheel rate. For sports cars, from 0.139 to 0.23; for passenger cars, from 0.026 to 0.071 .
|07-01-2010 03:13 PM|
Thank You Sam
Thanks for the help Sam, You advice is greatly appreciated. I think I'm getting closer to having enough information to at least talk intelligently with the spring manufacturer. With the stock springs having a 304# spring rate in the front and the 1st stage of the rear having a 175# spring rate(adds a 237# spring rate when you get on the 2nd stage overload section) total of 412#. I may be closer than I thought, with just the second stage of the rear being a bit too stiff.
I don't know what happened to Billy, he left me somewhere between leaving it stock and no more than 125# WHEEL rate, which I gather is my SPRING rate.
Again Sam, thanks for taking the time to discuss it. When you mention leaf spring suspension with a straight axle in most circles, people just tell you to whack that crap out with a torch and get IFS, then whack out the rear and get a four link. I just march to the beat of a different drummer, I'm gonna make this old buggy spring truck drive and ride good with the original design. No cutting torch required. Nolan
|07-01-2010 02:01 PM|
Personally I think I would go for about 300 or 350 in the front..the 125/150 in the rear is fine..you may wish for some aux airbags in order to stiffen things up a bit if you need to..this suspension stuff has lots of compromises to it in order to get a decent ride and it sthandling..Myself I like them a bit stiffer than some to get the cornering that I like..
You might wish to use the field expediant method and just remove some leaves from the stock springs and give it a test hop or two..if all the bolts are clean and well lubed changing a leaf spring is not all that hard.
|07-01-2010 09:19 AM|
Okay, So the wheel rate is the spring rate on a beam axle. With that understood, are you still suggesting no more than 125# spring rates at all four wheels?
Seems like the 125# would be too soft for the front given the 1995# curb weight of the front end, 1365# rear curb weight could definitely use the softer spring to get more of a car type ride considering I'm never going to put anything in the p/u bed.
Help me understand this. I'm going to have the springs custom built by Eaton as per this information. I appreciate you taking the time to discuss this.
|07-01-2010 08:50 AM|
With the springs bearing directly on a beam axle, the spring rate is the wheel rate. Obviously, lateral spring spacing affects the roll stiffness.
With an IFS (or in the case when the spring is mounted on a trailing arm attached to a beam axle), the linkage ratio must be taken into account. If the linkage ratio is, say, 1.5 to 1, the wheel rate is the spring rate divided by 2.25 (or 1.5 squared).
Stopped to do a little googling and found this:
His "motion ratio" is my "linkage ratio." Also, rather than work with trigonometric functions, it's usually easier to measure the distance from the pivot to the spring centerline on a line perpendicular.
|07-01-2010 08:23 AM|
Spring Rate/wheel Rate
Hey Man, Thanks for looking at my setup. So, you're saying to stick with the factory spring rates? How do you calculate the WHEEL rate versus the SPRING rate. Or visa versa?
The general plan is to just improve what the General(GM) put in it to begin with. I'm just hard headed and stubborn about cutting the suspension out and starting fresh, I want to keep the stock design and improve it to eliminate some of bad attributes.
When these old trucks are well lubed(solid leaf spring bushings) and with taller sidewall tires the front ride is not too bad. The rear on the other hand is way too stiff and jouncy without any load. Bumpsteer and steering box slop, along body roll are the other poor attributes.
The rack & pinion assembly I'm going to use is supposed to eliminate a great deal of the bumpsteer and make the steering more precise. The front and rear sway bars will eliminate alot of the body roll. I'm close to what I want, but need help in choosing the proper SPRING rates.
This is a street cruiser, its not like I'm going to try and run an autocross course with it. The ladder bar thing was just a discussion, I'll very likely run a slide-link traction bar system to prevent wheel hop and get a half decent holeshot if I want to bring it to the drags on Friday night.
Sorry about the long wind, but I'm trying to get help it the areas that I'm not too knowledgeable about. Nolan
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