95jersey

Ok, so say one has a set of coil overs. Obviously the spring sits on a pearch surrounding the shock. When one lowers or raises the car, what effect does that have on the spring rate?

If you take any spring and compress the hell out of it, it becomes very stiff, but if you let it have more travel, it seems to become softer and more pliable.

So if you raise the car (meaning compressing the spring) are you raising the spring rate? And the opposite when you lower the car and you create more spring travel, are you lowering the spring's rate?

Or I am totally wrong and the spring rate is what it is regardless of how it is compressed?

redtopz

The way I look at it is if you pre-compress the springs to raise the car you are not changing the spring rate but allowing the coilover to support more weight before compressing the shocks. For example, say you have 1000 lb/in springs and a 1:1 movement ratio with perfect corner balance on all 4 corners. If the car weighs 4000 lbs then the coilovers would compress 1" each at rest. However, if you pre-compressed each spring 1/2" then the coilovers would only compress 1/2" at rest (starting point). This is because each pre-compressed spring will support 500 lbs without further compression (2000 lbs total). However, anything beyond 500 lbs will cause the springs to react as normal 1000 lb/in springs (ie. no change in spring rate).

Similarly, on the track as soon as the coilover compresses beyond the starting position the spring rate is unchanged. It just takes slightly more force to get the initial movement started. A 700 lb/in spring is still 700 lb/in even if it starts pre-compressed 1 inch. Once the spring approaches full compression then the spring rate will rise exponentially.

I just raised the spring rates on my LG coilovers 100 lbs front and back. My car now sits higher and resists bottoming out significantly better than it did with the previous spring rates even though I had them pre-compressed quite a bit.

95jersey

I guess what I am trying to ask if I raise the car, does the ride become stiffer (even though the spring rate hasn't changed), and if I lower the car the ride may become softer?

dfinke23

If you lower the car, the ride will be about the same, but you will shorten the travel of the shock before it bottoms out. If you raise the car to the point the shock is fully extended, and then keep compressing the spring, you could stiffen the ride a bit.

....and I could be completely wrong about this.

95jersey

I have LG coil overs and they are shorter than OEM, so they won't bottom out even when pratically slammed.

BrianCunningham

good explanation

original I can my car too low, which also gave it real soft ride

now it's too high, and the 1st of the dual springs is almost coil bound.

40YRW8

OK, here's the deal. Where you adjust the spring has no efffect on the spring rate. It is a constant. To stiffen the suspension you can either increase the shock dampening (only stiffens during jounce/rebount) or buy springs wound for a higher spring rate. I am not sure what you guys mean by "Pre-compressing" a spring unless you are adjusting it so far up the shock that you bump it up against the shock travel limit. That would beat your shock to pieces in short order and, if the coil-overs were designed for your car, would make it look like a 4X4. Adjusting the coils up and down only change the ride height at each wheel. You can compress 2 of the 4 coil-overs if you put a lot of wedge in the car but at the same time you would be taking wedge out of the other two.
Gary

John Shiels

It would depend on how it was designed, no?


edit

found this article http://www.stockcarproducts.com/spgtech.htm
http://www.stockcarproducts.com/spgtech.htm

dfinke23

I may be thinking about this the wrong way, but the shorter the shock, the less travel it has and is more likely to bottom out.

BrianCunningham

he's right, unless the spring is stiffer, they'll bottom out faster

95jersey

Nope, LG coil over is shorter than OEM and designed to lower the car. Go read LG's write up on the coil over, it is designed to not bottom out even when the car is slammed. Your control arms may be out of geometry, but the shock will not bottom out (that is what drop spindals are for). The longer the shock, the more likely it will bottom out. The shorter the shock the less likely to bottom out. This is actually one of LG's top selling points, that his shock does not bottom out on lowered cars.

Put it this way, to bring it up to T1 ride height specs, I had to turn the perch about 10+ turns the way it came stock.

BrianCunningham

so what's the spring rate compared to stock?

95jersey

coil and leaf rates are hard to compare on just pure numbers, but I can tell you they are stiffer than T1. They are F'N great on the track. Car is so flat and responsive you can't believe it.

redtopz

No the ride (spring rate) will not change if you raise or lower the car. However, I also have the LG's and wanted to raise my ride height a little. What I did was build some 1/2" aluminum shims for the rear coilovers between the upper shock mount and the mounting point. In front I used a bunch of washers at the lower shock mount. This is a more effective way to raise the ride height than pre-compressing the spring.

40YRW8: By "pre-compressing" the spring we are talking about turning the lower nut in the coilover that holds the spring around the shock. If you tighten the nut it will compress the spring and help raise the ride height a little bit. The Pfadt coilovers have a different design that allows you to change ride height independent of the spring pre-load by turning the shock up or down within the coilover.

vette6aut0x

Lg has the same shock design. It is the GT2 coilover. A really good shock.

davidfarmer

spring rate does not change...but the geometry may cause a stiffening/softening effect. For instance, if the spring is perpendicular to the control arm originally, it will have a direct rate. If you raise/lower it to the point that it is at a steep angle to the a-arm, you'll need to multiply by the cosine of the angle to determine the change. However, if you lower/raise that much, you have probably messed up a lot of geometry.

vette6aut0x

Drop spindles, works every time.

hamdog

I have my LG GT2s body adjusted to as low as they can go in the front and the ride hasn't changed much if any from an already stiff ride. I believe the GT2s come with a 600 pound rating. I haven't had any issues with handling at the track with the car "slammed". If you're going to do that, make sure you make the adjustments via lower brace (shotening the body) before you get into the spring height adjustment. I believe this is what you are referring to when you talk about LGs claims of shorter shocks=less bottoming out. The ability to adjust the overall length of the shock body allows a ride height adjustment independent of the spring height. Great feature on the LGs,Phadt and other good CO products.

gkmccready

This is a Bilstein-ism... they build packages that have the spring go "solid" before you bottom the shock. You still "bottom out" but you exhaust spring travel before shock travel, this is also why you don't have bump rubbers... if you change springs watch you get the right length so you continue to run out of spring travel first...

redtopz

Oh yeah, I forgot about those. They weren't around when I bought my G2 coilovers.