I have had alot of calls and emails about choosing the correct spring rate for their car so I will give a rough overview of spring rates in hopes this will help.

First this is how spring rate is measured. The springs are measured in lbs per inch. An example of this is the QA1 spring for the front os our cars. It is rated at 315 per inch. This means that each inch you compress the spring changes by the rating. 315lb is 315 for the first inch, the second inch would be 630lbs and so on.



We will start with the front.

Most of the 4th gen f-bodies weigh in at 3500 at the high side, the weight bias(front to rear) is usually 54% front 46% rear. This equals 1890lbs front weight. If you run a QA1 spring at 315lbs usually the spring is compressed 5 inches per side. This comes to 3150lbs of spring on the front. NOW comes the trick. The spring shock setup is actually inboard of the spindle on our cars unlike strut front ends. The spring has to actually hold up more weight because of the leverage of the control arms. This comes to 40% more spring to hold up the car. Here lies the problem. The more you compress a spring the more "stored energy" the spring holds. When you launch the spring tries to throw the car up and relieve the stored energy. This ends up being a wheelstand situation if the cars hook.

The way to remedy this situation is to run a softer spring. We normally try a 275 lbs spring compressed to 5.5 inches. This lowers the total weight to 3024lbs BUT the car runs out of stored energy quicker so it will slow a wheelstand down. You could actually put a 225lb. spring on and compess it to 7 inches and hold the car up but kill the weight transfer.

Tightening the shock up on the front will not control the wheelstands as the shocks work to slow to overcome the spring. Only a softer spring or a limiter will control the front end.


Hopefully this will explain some of my spring theories.

 

Awesome info!!

With the HAL series "R" strut/shock setup what HAL front spring would you recommend (stock springs and HAL Series "R" shocks in the rear)

Can you get them in a 275 pound setup?

Raceweight around 3500 pounds?

 

Order the "Coilover" tops and get QA1 2.5 diameter spring. 14" 275LB

 

edit.

 

We arent talking about shocks. The spring puts the bounce in the shock controls it. This is more drag oriented cars.

 

excellent thanks Madman, does the same hold true for six speed cars like mine? I know automatic cars shock the suspension/tire alot differently

 

Good topic. i'd like to hear if there is a difference between a 6speed setup and a TH400 T/B setup.

Chris

 

hey chris, the springs on my car you asked about im almost positive are the 275lbs that brian is describing. you have to have some additional adapters (about 50bucks worth i think) for these to work.

if the 275's help control the wheelies im glad i didnt get the other ones.

great info brian, thanks

 

Brian,

What happens to the ride height in this scenario? Assume a car is set up with a 315lb front spring. Ride height is adjusted to a given level with the car race ready, driver aboard, just as it is on the starting line. Let's say the crank centerline is 12" from the pavement and, using your numbers, the spring is compressed 5" giving us a spring load of 3150lb.

Now we swap to a 275lb spring.

The downward force applied to the spring is unchanged, the total sum and placement of mass in the front end is the same. The lower spring collars are not moved. Except, now we have a softer rate spring to provide less resistance to hold the weight up. Given the above numbers, this spring willcompress an additional .75", lowering the chassis ride height roughly 1". At this point, the total spring load should be the same, 3150lb.

However, in order to regain our lost ride height, we will need to raise the lower spring platform by .75", thus "preloading" the spring and giving it more "stored energy".

Now the good part. Like you said, it takes 315lb to compress a 315lb spring 1", and it takes 275lb to compress a 275lb spring 1". So, once these springs are compressed a given amount to attain the desirable ride height, the reverse is also true. You will need to remove 315lb from a 315lb spring to extend it 1". You will only need to remove 275lb from 275lb spring to extend it 1".

Which is easier for the suspension to do and which is more likely to wheelstand?

Excellent tech article Brian. We need more info like this on here to make you think about how things work.

Jay

 

Awesome info!! Thank you Madman!!

PS: I sent you an PM.

 

You have some good points Jay.

You would have to compress a 275lb spring more to hold the car at the ride height of a 315lb spring. The theory behind going to a lighter spring is that the 275lb. spring will lose stored energy quicker. The 275 will be compressed more initially and hold more stored energy at ride height but once the car starts to extend the front end the spring starts loosing energy.

 

Is there anyway to relate this to the rear?

I just ordered a QA1, 300lb-12'' spring. My truck probably see's a 65-35 front to rear weight ratio of 4100lbs.

To restate the question. What should we look for- A heavier spring to soak up all of the weight-transfer and keep the energy stored?

Thanks,

Kyle

 

Are you saying you are putting a 300lbs spring on the rear???

If so you are bringing up a good question. The rear suspension is a different theory. You want enough spring to hold up the vehicle. When you launch the vehicle the rear end is slammed down from spring energy and suspension components. This is where you need a good shock to control the spring and pull the body down with the rearend.

 

What should we look for in a rear spring then? And I'm gonna guess that if you know what the weight is over the rear you can pick one that's better suited. But what kind of "formula" can you use to find that out(best spring after knowing weight)? I'm in the process of looking for a different rear spring then stock.

Chris

 

Are you looking for a stock style spring or a 2.5 diameter????


One thing to remeber is all these rates that I have given so far are for constant rate springs not variable rate like Eibach etc.

 

whichever one is gonna be more beneficial

It's a drag only 4th gen. I'm gonna assume too that the 2.5 spring is gonna give me more of a selection, even though there might be modifications necessary to make it work right?

Chris

 

Not sure what my car weights now after all the modifications, but I would guess around 3300 lbs. or less. I'm running stock SS springs all the way around with R series Hals in the front and the regular Hals in the rear. I dont believe that Hal makes but 1 shock for the rears. Anyhow, since this subject is up, what springs should I go with? From my last set up which wasnt optimize to say the least, I was only cutting low 1.6s but should of been in the high 1.5s. Im not sure what the car will do now with the new set up, but I wanna go back to the track and see nice gains. I dont wanna go with a spring that is too soft because I dont want to blow my shocks when I drive the car on the street. I dont drive the car very much at all, but I do wanna be able to take it out here and there. What do you recommend I do? Thanks.

 

Yes sir, the rear suspension. Ok, you want more spring lb. (numerically) for the rear to control the weight-transfer?

I will be using a QA1 shock, out-back also. I'll have to do some testing to figure out the setting. I got a problem w/ my vehicle. I have a huge weight bias on the drivers side (driver, battery, gas tank-lies parrallel along side), so you get less ware on the passengers side. Truck literally leans.
Do you know if off-set settings of the shock would cause a problem? Need to put more force on the passenger side rear tire.

I'm going way off topic here, sorry about this.

Kyle

 

Brian, where can I get some 2.5" rear springs for my car? I need some this week. you told me what rate to get, but I forgot If you want, just get them for me and ship them.

thanks
..Brady

 

Brady I will call you tomorrow.


Sportside5.3 what rear suspension are you running. Obviously you have dumped the rear leaf springs so I would run a 175 or a 200lbs rear spring on a coilover shock.