coil springs vs coil-overs for lowering your car

When you have decided to lower your car (Not A Truck) you have a couple of choices to chose from .. Lowering Coil Springs or Coil-Overs. First you must decide what type of car your building or why you want to lower your car.

  1. Just want it lowered
  2. Building a street car
  3. Looking for better handling
  4. All out race car for specialized type of racing

what is a lowered coil spring. Coil spring is made from spring steel or carbon steel with a certain amount of coil revolution to make up the spring. Manufactures engineer coils to lower your car and keep the oem geometry for alignment reasons. When looking for a coil spring to lower your car you will notice 2 things.

  1. amount that lowers your right correctly
  2. the spring rate

not all cars can be lowered extreme amount some times you only get like almost an 1″  other cars can be lowered 2.5″ it’s all in the type of car you own. why is this because of the geometry of the suspension and the ability to be able to get your front or rear car aligned so you don’t go through tires every couple of months.

Now on to what the spring rate does say you took a oem spring and cut a couple of coils off the spring would be shorter but you would change the spring rate from the oem spring rate. You would get a higher spring rate on a cut coil spring and it would be stiffer not a bad thing and It would give you better handling to a point. SPRING RATE Spring Rate refers to the amount of weight it takes to compress a spring a certain distance.  The higher the spring rate, the stiffer the spring.

To figure out the Spring Rate you start by compressing the spring about 20% of the available distance of the spring and measure the height (Load Length 1) and the Load 1 in (lbs/inch) or (N/mm). Then compress the spring about 80% and measure the height (Load Length 2) and the Load 2

(Load 2 – Load 1)
Spring Rate = ——————————————-
(Load Length 1 – Load Length 2)

Most springs are fairly linear, which means you would get the same Spring Rate from the equation no matter which distances you would use, 20% and 80%, or 40% and 90%, or 10% and 30%.

Some springs are non-linear, which typically means the spring gets stiffer the more you compress it.  One way this can be done is by changing the coil spacing, so that coils start to touch each other as you compress it.  Another way common in racing is for the spring to compress and then encounter an additional spring.  This increases the spring rate because now you have 2 springs acting on the force.  Many times this additional spring is a rubber “bump stop”.

WHAT AFFECTS SPRING RATE

  1. Wire Diameter: When the diameter of the wire increases so does the Spring Rate. When the wire is thicker it becomes stronger and more difficult to deflect.
  2. Spring Diameter: When the diameter of the spring increases the Spring Rate decreases.
  3. The number of coils in the Spring: As the number of coils increase the spring rate decreases.

 

Wheel-Rate-Sml

r3

r2

COIL-OVERS are a whole different type of part coil-overs are what most people would like because they have ton of adjustablility you can tune the suspension to your driving style. Coil-overs have the ability for you to adjust the ride height and they allow you to adjust the compression valving in the shock/strut  Not all coil-overs have the adjustment for rebound valving for the shock/strut and the pre-load can be adjusted hard core track racers.

What is pre-load on a coil over 

Preload is when the spring is compressed between its upper and lower perches on the strut body before the assembly is placed in the car. Basically its the length of the spring from top of spring perch to the bottom of the spring perch  on the strut body

A Simple Example With Preload

Let’s recreate the last example, but this time with a spring preloaded one inch. First what we are going to do is use Hooke’s Law to find the amount of restoring force (F) the 400lb/in (k) spring has with one inch of preload (x):

F = -kx

F = (-400lb/in)(-1in)

F = 400lb

What this F value tells us is that our preloaded spring is exerting 400 pounds of restoring force on it’s perches before it is even installed in the car. Now we need to install this preloaded coilover into the car. This is the point at which many people’s intuition leads them astray. When you factor in the weight of the car pressing down on the coilover you have to SUBTRACT its weight from the force already stored in the spring! So since our spring already had 400 pounds of force stored in it we subtract that amount of the 923 pound weight of the car:

938lb – 400lb = 523lb

Since our spring already had 400 pounds of force preloaded, the spring only has to absorb another 523 pounds (F). Let’s find how much additional compression will take place (x):

F = -kx

523lb = 400lb/in(x)

Solve for x:

x = -1.3in

So when we place the car’s 923 pounds on a spring preloaded one inch (400 pounds of stored force) it compresses the spring an additional 1.3 inches. Add this to the preload compression:

1.3in + 1in = 2.3in

 

Remember! Any force already stored in a spring acts against any force that is being added to it! This goes for all linear and progressive rate springs!

Compression valve adjustment

most all coil-overs will allow you to adjust the compression valving up to 27 different settings. Compression damping is the force experienced when the damper is being compressed. In the case of most vehicles, this is when the damper moves upwards relative to its mounting position; a good example is when you hit a bump at high speeds on the road. If there was no compression on your shocks or struts your tire would just move upwards along with the vehicle, losing contact with the ground. With compression, the tire will deflect over the bump allowing the damper to absorb the impact (hence the name- Shock Absorber) and the tire will extend back to its original state, all the while reducing the vehicle’s motion and not disturbing the comfort of you and your passengers.

compresion

 

Rebound valve adjustment

Rebound damping is the force that is experienced when a shock absorber returns from its compressed state to its original state. When a damper is in the process of rebound the spring goes from being compressed back to normal releasing all the tension from the compression. In some cases the ride feels bouncy or stiff because of the  spring rate and/or damping force settings not being compatible.  Keep in mind that if you have a damping force adjustable coil over the stiffer your settings are the slower the rebound. The softer your settings are the faster the rebound.

tech-shock1-300x201

Now that you understand a little better what the difference is on lowered coil spring and coil-overs you can now chose which to buy. We sale brand like

  1. TEIN SUSPENSIONS
  2. BC RACING COIL-OVERS
  3. K&W SUSPENSIONS
  4. TANABE SUSPENSIONS
  5. SKUNK 2 RACING
  6. EIBACH SUSPENSIONS
  7. H&R SUSPENSIONS

bc-racing-coilovers-ad

 

 

 

 

One other thing before we go.When ever you lower your car make sure you get some kind of a alignment kit. Some coil-overs kits have the upper strut mounts that have camber adjustment .

If your just buying lowering coil springs you can get alignment bolts for camber adjustment and some cars have offset camber bushings. Even if your car get a 4 wheel alignment they have rear adjustable control arms and track bars to keep everything in align.

If your going to lower your car do it right the first time don’t just do what your wallet allows you to do. Save the money buy the right parts you don’t want to damage your car just because you didn’t want to pay to do it right!