Back when I had my Max, Progressive rate springs were definitely preferred over linear rate offerings. I've been reading the Z/G forums and seeing some people prefer the linear rate. Can anybody let me in on why?

 

Linear springs are more forgiving and predictable than progressive.

 

I'm hoping for some more technical discussion here too. So which is bouncier? Which is better for the track or street use?

 

bouncier is not a factor of the spring. More a factor of your absorbers; as they control the spring.

Better for track or street? subjective some like one, some like the other.

 

On a progressive spring it does not have just one spring rate, there is a range of springrates. The springrate of a progressive spring will increase as it is compressed. On a linear spring it has one set sprintrate no matter how compressed it is. Linear is usually more desired on the track because of its consistent springrate.

 

So is it safe to say that, given similar spring rates, linear springs will be more uncomfortable in daily use?

 

No, just the opposite. Linear are more forgiving

 

I just don't get how the same springs can give you a more luxury ride on the street, yet be the best for track use as well?

 

Because they are more predictable.

Think about it like this. You hit a bump. With a linear spring, the spring responds with a give rate/spring pressure regardless how hard you hit the bump. With a progressive spring, the harder you hit the bump, the harder the spring responds to that force. This is the reason that linear are more forgiving (comparing similar spring rates). When you have a progressive spring, the rougher the road, the rougher the ride.

On a track, hard cornering will causing vary degrees of pressure on the spring. A linear spring responds with the same force where as a progressive has a range of responding force. As a driver on a track, the more predictable the car is, the better

 

sorry to jump in, there seems to be a bit of misunderstanding in this thread or i'm reading the responses wrong (and i'm sorry if i am reading them wrong and insulting anyone). I just got the sense triple8sol you were craving more info.

Progressive springs - correct that they have varying spring rates but more specifically progressive springs offer more resistance as more load is put upon them. That is, the initial rate is softer than the final rate. How the spring is wound determines the characteristics of the spring (progressive springs can be identified as one end has greater distance between the coils than at the other end of the spring). The lower initial spring rate achieves a compliant suspension over rough aspects of the road ("cushy"). As the car is pushed in the turns, the rate progressively increases to a tight suspension for high-speed turns ("tight"). The comprimise is the vehicle will react differently depending on where in the spring rate you are.

a couple of very simplified examples... for your definition of the nonspecific terms "predictable" or "forgiving" used above. others definitions may vary . this discussion is of course ignoring the many many other variables in suspension behaviour.

as for "predictable" - take the example a high speed tight turn at the track vs a slow sweeping turn of daily driving. You will be dealing with different spring rates as more or less weight is applied to the outside wheel spring, respectively. The "less predictable" nature is that depending on the circumstance the springs will react differently.

take another example of a high speed turn through a bumpy turn. The outside wheels (loaded) will be a higher spring rate than the inside wheels (unloaded) due to weight transfer outside. Now take the scenario of hitting a bump in that turn. The vehicle encounters a bump, the inside vs outside springs will react differently to that bump given they are at different spring rates. The attitude of the vehicle will change, making it difficult to predict.

there are of course many other ways springs influence the vehicle, that i won't get into or else this post will go on forever. there are many books on suspension dynamics out there for your perusal.

So why you ask, would anyone want a progressive spring? Two scenario's.
Scenario one: In the case that you know a every aspect, bump, forces, etc. of a single specific racing track very well. Typically with suspension telemetry, suspension engineers may feel that custom progressive springs work to their advantage by customizing the rates to the specific track in certain very specific circumstances. This is absolutely not, obviously, the use of a typical z owner.
Scenario two: the daily driver that wants a "cushy" ride over harsh aspects of street driving (hiting potholes/manholes/or any other hole or bump for that matter) but when getting on it and having fun in the twisty's and turns of a canyon run while enjoying the increase spring rate in those turns.

Linear springs - the spring rate is the same regardless of the load upon it. Slow sweepers or fast tight turns the rate is the same thus more predictable. The same arguement goes for bumps as the springs will react the same to bumps regardless of the situation (again ignoring other suspension variables).

Soooo, why get linear springs?
Scenario one: comparied to scenario one above. When you are racing the car at several tracks and don't have the budget, telemetry, or dedicated suspension team to customize your setup (custom springs to the track). You get "predictable" suspension as it will react the same regardless of the track. Linear springs are for you.
Scenario two: for street driving where you're willing to "sacrifice" the cushy ride, if you consider that a bad thing, for a "predictable" suspension. Most street drivers dont push the vehicle to these limits, but may want the option to do so (on a track of course ).

SO why not get linear springs? If you are looking for improved handling, less squat or dive, then you are looking at higher spring rates. Higher spring rate linear springs are therefore not more "luxury" as you put it triple8sol, if that's your definition of "forgiving". I think that is a misunderstanding between you and Zivman. If you want that cushy ride on daily driving, you won't get it in a higher rate linear spring because rate is high regardless if it's initially or finally. However, there are linear springs of varying rates that you may choose from from near stock to higher or lower (eg. hotchkis near stock, RSR down spring slightly more than stock)

a great very brief read is this technical orientation
http://www.hrsprings.com/site/about/manufacturing.html

hope this helps

pp

 

This is not true. Triple8Sol, you have the right idea. A progressive is typically more comfortable then a linear spring.

 

Thanks for jumping in and confirming thawk. It's not just me that thought that there is a misunderstanding between triple8sol and zivman over what is more "forgiving"

It really depends on how you drive and how you want your car to behave. These of course are generalizations, and there is a spectrum between, but give you a start on where you may want to be.

1. Daily driver, rarely if ever push car to limits. Willing to sacrifice predictability for some comfort, or "forgiveness".
Progressive is for you. +/- spring rate matched shocks +/- sways to tweak

2. Agressive daily driver or ocassional track use. Don't mind harsher ride of a higher rate linear spring. Prefer predictability and willing to sacrifice some comfort (if going higher rate)
Linear may be for you. Match with shocks. Tweak with sways.
* triple8sol, your comment that "most" seem to recommend linear springs on this board comes from the fact that many z driver's see themselves in this scenario *

3. predominantly track: Depending on how serious you are and the expertise available to you. Linear is most often the way to go, unless you have data that a specific custom progressive setup is better for the particular track that results in better times (competition). Obviously, setup includes (multi-)adjustable matched shocks, sway tweaking, alignment tweaking, weight balance, etc etc.

#2 This is me --> 2-3 recreational track days a summer, agressive daily. Don't mind higher initial rate harsh ride. Research is ongoing but settling on adjustable koni/RSR down linear/sways/bushings. would like slightly higher rate than rsr. thought about full track #3 but realized my use doesn't justify.

all depends on where you want to go with your z

pp

 

I was definitely looking for some more detailed info, and this is great stuff guys!

I would classify myself in category #2 also. I just participated in my first autox yesterday. It was a blast, and I will be going back as much as I can. The only thing that I would still debate is that I have a G35c, and not a Z. Wanting to preserve some of the luxury ride/comfort is something I take into consideration too. Sounds like I"d have to decide whether giving up some comfort in daily driving is worth it for the 1-2x each month that I'll be going to autox or the track.

Now when I'm looking at specs from spring manufacturers, they only list 1 spring rate for each spring, regardless of whether it's progressive or linear. When looking at a progressive spring, would that given spring rate represent that spring at full compression?

 

What kind of suspension are you looking for exactly?

 

[QUOTE=Zivman]Because they are more predictable.

Think about it like this. You hit a bump. With a linear spring, the spring responds with a give rate/spring pressure regardless how hard you hit the bump. With a progressive spring, the harder you hit the bump, the harder the spring responds to that force. [QUOTE=Zivman]



Actually, this is not correct. The behavior of a linear spring is actually:
F = k * x, where F is the force required to compress a spring with rate, k, a given distance, x.

A spring with a progressive rate behaves like:

F = k(x) * x where the rate, k(x), is now dependant on x. So how fast you compress the spring has no effect on how hard the spring pushes back, it only depends on how far you compress the spring.

The force you get from a shock absorber is, however, dependant solely upon the speed at which you compress it:

F = c * v, where F is the force you get from the shock with damping constant c as you compress it at a speed v. This would be for a linear damper, but all shocks are really designed to be non-linear and have some sort of damping "constant" that changes with speed, c(v).

So, overall the force from the shock and spring combined is:

F = k(x)*x + c(v)*v + m*a, where m*a is the unsprung mass (wheel, tire, hub, 1/2 of suspension arms, etc.) times the acceleration of the unsprung mass. This is a 2nd order differential equation and is called the quarter-car model by vehicle dynamicists (since it models the behavior of one wheel).

What was the subject of this post again...? Oh yeah, so a progressive rate spring exists only to lessen the tradeoff between a ride quality and body roll. Progressive springs start out soft so you don't feel all the little bumps in the road. However, the further the springs compress, the more force it takes to compress them so you can design the springs to be soft for, say, the first inch or so of wheel travel and then stiffen up to keep body roll to a minimum.

I've never raced back to back in a car with linear and with progressive springs, but I would suspect that the linear springs are indeed a bit easier to predict as a driver.

-EDIT-

I didn't read Palepony's post before responding, so sorry if the info is a repeat.

 

Forgiving and Predictable are being confused it seems...

I think the way most people are thinking about it is Forgiving as to bumps in the road and forgiving to things that make the ride harsh... Yes progressive springs will make small bumps more comfortable... Those same small bumps and hard bumps will effect the car just about the same (Depending on damping of the shocks)...

Driving on the track with progressive springs (like eibach pro-kit) is scary, when you go into a corner hard, the car is unpredictable and you dont know if the car is going to stick through the corner or break loose...

But driving on the track with linier springs / coil over set up your car feels solid no mater how hard you are driving... They are predictable to the fact that they always feel the same...

(the above also depends on your tire size / tire pressure / other suspension set up / shocks etc... these may not be the case in every car etc...)

 

are the stock springs progressive or linear?

 

Linear.

Though in the most technical sense the front's are slightly progressive because they are not a consistent outside diameter. However, it's not enough to merit mention as the rate spread would be very small with no binding coils. Tein's tapered 82mm to 70mm springs are considered linear by Tein as a example.

 

thanks dude

im still having trouble understanding the difference, but for what i want the hotchkis seems the way to go.......that is lower ride height (more rear drop than front to eliminate the dragcar look) and similar spring rates to stock

i think ill wait till i can afford to buy the sway bars as well