7 replies to this topic

[TRD JZX100]

What is Spring Rate?

Spring Rate is the amount of weight needed to compress a spring a certain amount. Springs are rated in LB/in (in metric system kg/mm), or specifically, how many pounds of weight are required to depress the spring by one inch. To convert LB/in to kg/mm international, you must divide divide figure by 56.

Consider you have 2 springs having different spring rates: One with 3.45 kg/mm and the other with 4.80 kg/mm. So what does it mean?
It means the 1st spring will compress 1 mm if you put a load of 3.45 kg, while the 2nd one will not. The 2nd one will need a 4.80 kg. load to compress 1 mm. According to this, we can say that the 2nd spring is harder than the 1st one, or we can state that: Springs that have a low Spring Rate are soft, while springs that have a high Spring Rate are stiffer.

If there are 2 different values listed, it means that the spring starts at one rate, and ends at another rate under full compression.
For example: a 10lb to 25lb progressive spring will need 10lb to compress it the first inch, then 13lb the next inch, and so on, until the end of the travel; it will take 25lb to compress it the last inch. The benefit of this is that the spring can be soft enough at the start of the travel to offer a soft ride yet be stiff enough at the end of the travel to performance well during hard braking and turning.



What Affects the Spring Rate?

There are 3 things that affect the spring rate:
1. Diameter of the wire: Diameter of the wire itself affects the spring rate because when diameter of the wire increases it gets stronger, meaning a wire which is harder to compress. So, if we know that a wire becomes harder when its diameter increases, we can say that: When wire diameter increases, spring rate increases.

2. Diameter of the spring: That is in fact 'the mean diameter of the spring', achieved by subtracting the diameter of the wire from diameter of the spring:
The overall outside diameter of the spring (mm) - diameter of the wire (mm)
When diameter of the suspension spring increases, the spring rate decreases.

3. Number of Active Coils (length / height of the coil spring): Determination of the active coil number varies according to spring design. Total coil number -2 for springs with both ends closed. Count the total coils -1 for springs with one end closed and one end open.
As the number of active coil decrease, the spring rate increases.

 img_spring_rate.png   11.75K   1 downloads




What are the Different Types of Springs?

1. Normal Springs has a fixed spring rate.
2. Step Linear Springs are springs which have 2 different spring rates.
3. Progressive Springs have a variable spring rate.


1. Normal Springs (Linear rate Springs, Specific Rate Springs)
 img_spring_normal.jpg   5.76K   2 downloads
In a normal spring, spaces between the coils are equal. Normal (or linear rate) springs are designed to respond with a specific rate when compressed.
Consider we have a 10-coil spring, each coil spaced 2 centimeters apart. Put a load on the spring to compress it 2 centimeters. Because in Normal Springs coils compress at the same rate, this 2 centimeters will be divided into all 10 coils equal, resulting each coil spaced 1.8 cm apart. Put another additional load which is the same as the first one and the coils will become 1.6 cm apart.


Step Linear Springs (2 Step Linear Springs)
 img_spring_step.jpg   5.67K   1 downloads
These are springs that have 2 different spring rates.
In a two-step linear spring, about half the coils have shorter spacing. As the spring compresses, the coils move closer. At a certain point, the shorter spaced coils touch, effectively eliminating them from the spring. You then have a spring comprised of only the longer coils. This "second-step" spring will be much stiffer than the whole spring (the more coils, the easier it is to compress the spring). The result is that you have one set of handling characteristics before the shorter coils touch and then you have another, completely different level of response after they touch.


3. Progressive Springs (Rising Rate Springs, Progressive Rate Springs, Progressive Wound Springs)
 img_spring_prog.jpg   5.63K   1 downloads
In progressive springs each coil is spaced differently and have a variable spring rate. When free, it is easy to compress progressive springs for the first few centimeters. As you apply more forces, the coils on a progressive spring come closer. After a certain point, coils at the top 1/4 of progressive springs begin to touch each other and finally become inactive or dead, and that makes the spring stiffer. Apply more force to a progressive spring then it becomes stiffer because as the number of active coils in a spring decreases, the spring rate increases. So, progressive springs may both be sensitive to very small bumps on the road, while giving the stiffness you need during hard braking and turning.




What's What?

Each spring design has its own market.

Progressive springs are likely "all-in one" solutions. Progressive springs are often used on performance aftermarket kits like Eibach or others, and they are good for daily performance street driving. They help you achieve the highest performance when driving hard, while providing a smooth, comfortable drive the rest of the time.

Linear springs are more often used in drag racing, road racing, track and races that require a "high spring rate", in which a constant spring rate is more important than a smooth ride.

They are still popular because they are:
-Easier to produce and can be made to lower a car beyond the point of progressive springs.
-Easy to work with, because spring rate never changes, allowing quick chassis setup
-Cheaper than progressive springs, allowing most race teams to use several different sets depending on track conditions

Linear springs...no matter how hard you compress them, they will always have the same resistance

Progressive springs...the harder you compress them, the more resistive they become...thats why the progressive springs have a 425-530 lb/in rating...first inch they are 425 in/lb and then get more resistive after that

The reason the progressive springs are good for stock struts is because they do part of the dampining. Linear springs do not do any of the dampening.

[5hu7o]

awsome write up marc! now i gotta check mine when there out?

[TRD JZX100]

Not a problem mate. Not as entertaining as my pictures in the shoutbox last night but still wothwhile (i guess)

[Wanjayzee]

Thanks Marc, ive always wanted to know the difference and what the figures really meant. Etuner explained it to me last friday and now you've just confirmed it... Powah to the root!

Cheers

[TRD JZX100]

See, i'm not just full of interesting internet pron pics I have some knowledge (a.k.a. mad cut & paste skillz) too

Just figured we need a bit more techy stuff on here too

[Sonic]

in my experiance you should stay away from the progressive and 2 stage wound springs as they are no good on height adjustable coilovers. plus over time the softer wound sections will lose its tension and compress, leaving only the harder rate working.

good write up though Mark

[S0unIQ]

Very good, Now all we need is a write up on the dampers. From what I've been told Springs and Dampers work in conjunction, so if you want a softer ride, ideally you need to change both units, yes?

[Sonic]

the dampening and spring rates are matched together when the shock is designed. typically if you put a heavier spring rate on a standard shock, the standard dampening wont be able to control the rebound of the higher rate spring.
even the dampening in expensive coilovers are designed to control a particular rate spring. the dampening adjustment provided will probably work if you only change the spring rate slightly but idealy you'd need to get the shock re-valved to suit the new spring.
one of the main problems is the poor actual design of the basic shock itself, almost all the aftermarket brands of coilovers are just 'emulsion tube' design, where a simple plunger is forced through the oil and the dampening is just the amount of resistance from forcing the oil through a couple of holes. these types of shocks are adjusted by changing the amount of holes that the oil is forced through. this design is only really able to handle a certain range of linear spring rates. this type of dampening can be the problem with duel rate or progressive wound springs. if the spring fully compresses and the shocks valving is set to suit normal driving conditions, the increased spring rate and force of the compressed spring can rebound too fast and cause the car to bounce. alternately, if the dampening to set to suit the higher rate of the compresed spring, then the dampening may be too harsh when the spring compresses slightly.

on very good quality shocks there is a cartridge inside the shock body (or sometimes the remote canister) which has a combination of bleed holes and shim stacks to control the movement of the fluid and the shock, also as well as the seperate external adjustments for 'compression' and 'rebound', these can also have another seperate adjustment for 'hi-speed' and 'low-speed' dampening, but then even these will not really suit a variable wound spring.