How much preload for optimum handling in coilovers? Bottoming out in the GS300

[overb0ost]

I've done various searches and I've read different answers and broad range answers.

I have a Lexus GS300 with stance coilovers and I'm trying to improve the handling on this beast of a car.

Car is about 4,000lbs and spring rates are 14/10.

When I had my s14 I preloaded my stance coilovers about 1/4".

Now with the heavy GS300, would 1/4 suffice or would more be required to reach the optimum handling.

Right now the car bottoms out on dips when traveling somewhat fast and this is at 1/8th" preload all around at 5/16 setting on dampers.

I've read on zilvia and ZT about how people calculate how much preload is optimal before it becomes a disadvantage. How is that calculated with static weight and the other variables?

PS: I'm asking you guys because I've searched preload on other Lexus forums and nothing comes up. Seems like s-chassis guys are more in-tune with suspension knowledge.

[slider2828]

Well here is my limited knowledge. Preload will shorten the travel of the coilover, so preloading is basically useless if ride heigh adjustability is independent of the spring. If they are the stance's which are pretty much ride height adjustable independent of spring preload, then adding preload will effectively reduce suspension travel and in your case won't help you.

Also I assume these springs are NOT progressive and should be linear, but they are cheap springs, so the more compression there is on cheaper springs, the spring rate actually falls to less than <14/10.... Trust me..... its proven

The only way to do things correctly is increase spring rate/quality of the spring or corner balance the car, which maybe very helpful as your heavy car would probably be front heavy.... Quality springs would be swift, hypercoils, and maybe eibachs but I would go with the prior 2.

[overb0ost]

If I got swift springs, would I then need to revalve the coilover to accomodate that spring type?

[Def]

Optimal preload for best handling on a sedan based car is ZERO. Unless you think limiting already low droop travel even more does good things for your car(it doesn't).

It sounds like you either need to raise up the car or run higher spring rates.

Swift springs are overpriced IMO - Hypercoil or Eibach are perfectly fine.

[slider2828]

Like I said swift or hypercoils... never been a fan of eibachs....

Match or go +2 in the front and rear should be ok.... If in double contact manufacturer....

Even running same spring rate will reduce the chances of bottoming out, but best bet is to just go +2 on a fat car like that.

[ayuaddict]

Basic coilovers can handle a +/-2 kg/mm difference in spring rate before they will need to be revalved. if necessary go +2kg/mm all around, and set that shit on full stiff. And preload it a little bit. 1/8th to 1/4th of an inch sounds pretty okay.

[!Zar!]

Keep in mind that that car has double wishbone, along with different suspension geometry. So it doesn't need as stiff a spring like our cars do.

Set preload at zero, and start from there.

The lower you go, just stiffen the damping up.

Let the shocks do their job with the spring. A bunch of preload will just make the car feel like a pogo-stick. No point in that.

[overb0ost]

So would a different set of springs like hypercoils in the same rates 14/10 be stiffer and perform better than what Stance has put on? Or is it necessary to go +1-2 higher all around to see better handling?

The thing with 4drs is that its all fine and dandy when no passengers are sitting in the rear but once 2-3ppl are in the back, the suspension drops another 2" lower.

Also, the worst is when hitting dips in the road like on the touge and the car just bottoms out.....I think I will try to adjust the preload maybe 1/4 all around and stiffen the dampening to 12/16 and go from there.

IMO, when there is no preload I find the ride a bit bouncy when hitting wavy roads. Small amount of preload works well from when I had my 240sx (yes, different suspension setup) but it felt better.

I do understand that when preloading the springs, it reduces the suspension travel but I think 1/4" preload wouldn't affect travel that much for me to notice unless I was racing on wavy roads all the time to make use of that suspension travel.

[Def]

I'd up the rates at least 2 kg/mm front and rear, maybe a little more. Raising it up just a hair might help as well.

[Def]

Keep in mind that that car has double wishbone, along with different suspension geometry. So it doesn't need as stiff a spring like our cars do.

Set preload at zero, and start from there.

The lower you go, just stiffen the damping up.

Let the shocks do their job with the spring. A bunch of preload will just make the car feel like a pogo-stick. No point in that.

Most double wishbone cars have very reduced motion ratios compared to a strut/multilink suspension. So they will need much higher spring rates to get the same effective wheel rate.

i.e. a 14 kg/mm spring up front might give the same wheel rate as an 8 kg/mm spring on an S chassis, but you're dealing with a car that weighs at least 1000 lbs more, so you need higher spring rates to control that mass when running low.

[s14unimog]

I run flex's on my 240 and contacted Tein about preload. They told me that excessive preload will do no more than cause excessive wear to the pillow ball mounts. They recommended 5mm's past contact; which isn't much. The Flex's preload is independent of their height adjustment.

One thing I've noticed that isn't recognized much is the effect of high offset wheels is relation to leverage on the suspension. I'm sure the answer is a high rate and revalving; if you're going to do it right right.

[shogun!]

Helper springs do good for droop.
http://200sx.kicks-ass.net/shogun/img4c1bc211d77b7.jpg


Preload without helper springs shall be set to zero. Some information that may help you out a bit at least.
http://200sx.kicks-ass.net/shogun/img4c1c63bbe3d91.jpg

http://200sx.kicks-ass.net/shogun/img4c1c63cb278c8.jpg

[s14unimog]

Helper springs do good for drop

And that's related here again how....?