why 620's over stock springs

mdjay said:

......600# and KYB's in the front are a nice combo for a SB on the street

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I just dont see how you could make this statment. I have maier 600# an kyb's and I cant stand it.

Tyler

I ran it for years and loved it...

Also Tyler, those Maier 600# springs are more agressive than the MP 620's...

There's lot's of people running this set-up and love it.

I don't know the stance of your car but if you drop the rear, the balance of the car equalizes and improves the ride comfort...

I have 620´s and Kyb´s in front and I´m satisfied with them. I have kyb´s with 5-leafs out back, and have some wheel hop problems, with shelby traction bars. Next I´m going to try different stocks out back, if that could help.

What happened to those Eibach progressive springs?

We have the 620s on my dads car with konis all the way around and that thing is so tight it just takes turns like none other.

I have the older Eibach progressive rate springs Pro-motorsport engineering used to sell. They still offer this spring by another manufacturer. They are the 480 to 680# competition springs. They ride smooth for everyday driving but have the stiff rate when you lean on them. If you are going to run a conventional suspension setup this probably the direction you need to go. This will keep your feelings in and your kidneys in good shape.

mdjay said:

I'm no pro! I just know from what I've seen, driven and discussed.

I've heard the contradictory, heavier spring rate and less bar, the driving style pref. quote is key.

With more sway bar, you are lifting the inside tire when the body rolls. The sway bar itself is a spring. Most of the racer's that I know tend to go toward the higher spring rate theory and less bar. Especially in the back.

Mike Maier seems to do pretty well with the higher spring rate theory. Granted he can drive the piss out of any car

We're talkin' race cars here so this is in extreme applications. Street driving applications are more forgiving and you would set the car up more for versatility (ie somewhere in the middle).

600# and KYB's in the front are a nice combo for a SB on the street

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I've seen Mike drive as well and my god is it amazing. But in addition to his driving talent, you also have to look at how his car is setup. The suspension geometry of his car is nothing like ours.

That's why I said to check out Herb Adam's book. It gives a good base line knowledge to use as a starting point to understand what's going on with our cars.

Example:

We can agree that the stock geometry, or even the Arning/Shelby drop do not give us the ideal camber curve. Therefore, *to control the camber changes caused by body roll, you need to limit the roll angle by changing the roll stiffness of the suspension.

Herb Adams Chassi Engineering said:

The two most common means of controlling the roll stiffness on any given car are via the springs and the stabilizer bars.

Increasing the spring rates will reduce roll angle. Unfortunately, raising the spring rates can also change other aspects of the car's handling. As an example, if a car had a front spring rate of 700 lbs.-inch and a roll angle of 2 degrees, and you wanted to reduce the roll angle to 1 degree, you'd need to install 1400 lbs-in. front springs. This would double the roll resistance. But increasing the spring rates this much would also upset the ride motions and cause the car to understeer.

The best way to increase roll stiffness is to increase the size or effectiveness of the stabilizer bars. If a car is to roll, one wheel will be up in compression and one wheel will be in drooping down. Stabilizer bars limit the roll angle of a car by using their torsional stiffness to resist the movement of one wheel up and one wheel down....Since the forces that cause the car to roll are being absorbed by the stabilizer bar, and these forces are fed into each lower control arm, the outside tire loadings will increase as the stabilizer bar twists.

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So, with that said, the theory is you run the lightest spring you can get away with. Now, if you're lifting the inside tire (as per your example) then that would be a situation where you would probably want to try less bar and more spring. It doesn't mean to chuck your 500lb springs for some 700's and ditch the sway bar. It's all about tuning. Same can be applied with the rear. You always hear about people who run stiff rear springs and say their car handles like crap with a rear bar. The most likely cause is there's too much rear roll stiffness.

The other thing about running a stiff spring is that the stiffer the spring, the harder it is for the wheel to follow road bumps and irregularities.

As I said, it's theory. Not until you start actually putting theory to the test will you know what works best for you. From a tuning perspective, it is much easier to tune with stabilizer bars than it is springs. Adjustable stabilizer bars are the cat's meow and allow you to adjust the roll stiffness quicker and easier than swapping out springs. However, it is possible that even after running through the full range of your bars adjustments...you might end up needing more spring.

And to clarify, I run Maier Racing 620's and a Maier Racing 1 1/8" front bar. I have a Maier Racing 1/2" 3-way adjustable rear bar that I have yet to put on my car. The difference the front springs and bar made are incredible. But there's definitely room for improvement. But before I put the rear bar on, I need to stiffen up the car first. Only then can I get the most out of my suspension tuning.

* paraphrasing Herb Adams

the two seemingly opposing theories on suspension settup are actually after the same end, getting the roll stiffness front and rear properly balanced for the most neutral handling possible. both theories have their proponents and opponents, but both have been used to great effectivness. there are also those, like me, who allow the fact that there are situations where one theory works better over the other. example;

on a smooth race track, it is better to use stiffer springs, and tune the suspension with shocks and sway bars.

on a rough track, or the street, it is usually better to use softer springs, and stiffer sway bars, and tune the suspension with shock valving.

while i usually subscribe to the latter theory, i can, and have, seen the former one work very well. it all depends on how the driver like the car set up.

Great info guys....

By the way, Mike runs around Hayward in a race prepped 67 fastback with slicks

I had the ride of my life with him in the 67! I've always felt I was pretty good until I rode with him. He is one of the best susp. tuners/drivers I've ever met.

Which KYB's is everyone talking about?

Gas-A-Just
or
GR-2


Thanks,

kwkenf said:

Which KYB's is everyone talking about?

Gas-A-Just
or
GR-2

Thanks,

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Please specifiy which ones.

They're all talking about the Gas-A-Just ones.

The GR2's are soft.

I know I am, but further investigation leads me to think that G-A-Js have soft low-speed valving and pretty firm fast valving. Cruising along over rolling bumps my car is like a boat, but hit a speed bump faster than a walking pace and it'll knock fillings loose.....and mine are composite.

So would the GR-2's be to soft? Manly driven on weekends only.

Thanks

I have 620s in my car, and I love them. I have considered going to 7XX rate springs. I currently have the stock shocks; I'm going to change shocks before I make up my mind on springs.

Regarding spring rate: if you are racing you want to run extremely heavy springs. There are multiple reasons, but a few are: to limit suspension movement because it's impossible to create "perfect" suspension geometry, and limit suspension movement for aero (you don't want a lot of air under the car so you need parts of the body very close to the road).

Spring rate on a street driven car is entirely different. I remember a number of years ago reading about that year's Mustang Cobra being set up with softer springs than the GT and actually ending up being quicker.

Good posts on roll stiffness as well. You want the roll stiffness in the front and rear of the car to be as nearly equal as possible. Otherwise you end up working one tire harder than the rest and your corner speed is reduced.