Someone posted some tables that made me wonder. Is the spring rate per side or is it both side together? lets say that you have the stock lightest spring when new rated at 196 inch pounds. Lets say that the rear two tires have 1600 lbs on them. If the rating is both sides together. Then from when you lower the car on a jack to sitting static the rear tire would have 8 inches of vertical travel. Or is the rating per side and will only compress the rear by 4 inches?

I believe that it is a one side rating. I bought a 520# rear fiber mono to replace my 500# rear steel. It doesn't move very far when you put the rear tires on the ground or if a 250 # person pushes down on the rear fender it doen;t compress an inch

 

This thread seems to indicate a 520# spring would be 260 per side, not sure which is correct.
https://www.corvetteforum.com/forums...ing-rates.html

 

Found something else giving a formula for spring rate and the length of the spring is part of the formula
http://www.trucktrend.com/how-to/cha...l-spring-rate/

 

Does anyone know for sure how the mono springs are rated? I was looking into rear coil overs today and the kits were 400# for SBC and 500# for BBC. Which would be in line with my 520# rated mono being 1040 # total to compress one inch.

 

Table from a 1972 AIM clearly showing the rate of a 304 lb F41 spring cut in half "per side"
The geometry of a coil-over attached to the rear is going to be severely "tilted" causing a severe reduction in wheel rate for a stiff spring. This causes them to need very stiff springs in the rear especially when angled 45 degrees. The Motion Ratio gets very low, and it is squared in the wheel rate formula.

The stock vette rear has fairly close to a 1:1 Motion Ratio and wheel rate.

I believe when you put the coil-overs in the front it is entirely different, because they go in the stock mounting locations, and maintain the stock motion ratio. So you can compare stock front springs to coil over springs.

I would need some rear coil-over mounting location measurements to be able to calculate the rear motion ratio for you. Then you could use that to compare leaf rates to coil-over spring rates. I am willing to do it if you access to the numbers. Even a very clear photo might do if it has something in it that I can scale.

 

PM sent

 

OK Gkull I know you like to race, so I found a way to calculate the motion ratio of a coilover system and compare it to a leaf spring system:




The left to right Motion Ratio is pretty severe for a coil over system because the lower mount is well inboard of the trailing arm. I estimate the two lengths as having a M.R. of .685. This means the spring only moves 68% as much as the tire. There is also a front to rear Motion Ratio which would be much smaller.But I can't measure it if I can't see or estimate it.

The bottom line is a 304lb/in steel F41 leaf spring would give the same Wheel Rate as a coilover spring with 375-417 for each spring.
For your 500lb monoleaf you would need 650 lb coils to feel the same.

I hope that helps.

 

That's all assuming a vertical coilover installation correct? If the coilover shock is placed at angle like the ridetech setup, damping effectiveness is reduced and spring rate must be even higher to compare to the leaf spring rate, correct?

 

Absolutely correct! The pic above is a vertical shock Van Steel setup. As far as I remember both the ride-tech and the shark-bite coil-overs have the rear shocks steeply angled, like 45 degrees. So that changes the geometry again.I do not believe it it as severe a correction, but it still has an effect. Where the lower mounting point is in relation to the axle or trailing arm C/L is the biggest ratio effect.

If you are interested can you get me a good clear pic?

 

I received pics of a sharkbite coilover setup. Very pretty!
Mounting position MR = 107/135 = .793




So the individual wheel rate of a 304 lb F41 spring is 196 lb according to its Motion Ratio.
A 600 lb coil on a shark bite suspension would give the same wheel rate.
And a 400 lb coil on a Van Steel coilover would give the same wheel rate.

So if you were looking to convert from a leaf spring rear, and wanted to maintain your current wheel rate, you could take the the Leaf Spring Rate and multiply by:
1.33 for a VanSteel coilover
1.97 for a Sharkbite coilover
And the wheel rate would be the same.

I hope this helps!

 

Because of the rocker system, won’t this essential be theoretically vertical! I have never studied like Indy car or IMSAtype rocker systems, or worked those type of formulas, but the mounting angle going thru a rocker would change things!

 

I'm sorry but I do not understand the question. Help me help you.

What I do know about linkage systems, IE: Indycar, is the springs could care less what direction they are pointed in, they only care about the force applied. They could be absolutely horizontal and hold up the car. Or vertical and use exactly the same spring rates, as long as all the linkage rates are the same.

 

I wasn’t a question!

Yes, what I said in my post the same as you wrote.

So doesn’t that Shark Bite thing have rockers? And thus angle of shock/spring does not matter!

 

I also never did get conformation of whether lets say a VB&P 420# mono spring is a per side rating or a total of both sides? Lets say that your rear tires have 1/2 the weight of your car on them. Lets for even numbers say that your two rear tires have 1680 pounds on them. You install the 420 inch pound spring. Does the spring compress 2 inches or 4 inch when you set the car on the ground for static compression?

 

The fiberglass spring in the 82 is 185lbs PER SIDE....without any 'stiction'.

Oh and to answer Gkulls original post headline literally...8lbs! lol That's how much a rear fiberglass spring weighs

 

The entire rear end is out of my car now but more like 4"
VBP 420#

 

Yes the Sharkbite has a rocker pivot. And if you look closely at the photo it has a different length to each end bolt from the center pivot bolt. The shock side, only has 72% of the length of the wheel side.. So this is a second motion ratio, in addition to the trailing arm, and means the shocks move much less than the wheels and is the reason you can run very very stiff springs on a .SharkBIte car and it still rides OK A Sharkbite car would have the same wheel rate and basically ride the same with two 600lb springs as another car would with the single 304 lb F41 leaf spring.of

And yes the leaf springs are measured for the whole spring. In a Vettes case this is two wheels. See the Chevy chart in post #5 where both "spring" rate and "per side" rates are mentioned. Stock is 70 lb per side. (This would be for the 9 leaf variable rate spring 6+3 variation with 3 straight top leaves).

You cut the rate in half for each side. And then multiply by the trailing arm motion ratio (squared). So the stock 70 lb per side becomes 116 at the wheel.

420 lb spring would be 210 each side, But there is also a motion ratio in the trailing arm, so 210 times 1.29 gives it a wheel rate of 349

A stock 82 has a 182 lb spring rate leaf spring correct? So per side is half at 91. Multiply by the trailing arm motion ratio of 1.29 (squared) gives that car a at-wheel rate of 151.