My HKS coilovers are going to kill me!!!
 

So I bought a gently used HKS Hyper coilover setup from this kid in japan. Worked on my car for about a year and then went out driving it. At the local auto-X the car handled very sharply but on the long sweepers it would bounce up front, almost hopping the tires the air. I drove this thing on the streets and it is sooo stiff that I fly out of my seat and hit my head onthe roof, it is also hard to keep my feet on the floor. I hit a bump and my gas and clutch foot go flying up off the floor board.

So I was mearging onto the highway yesterday and on the on ramp i got on the gas. there was a bump on the on ramp and it shot the car over 1 entire lane.

Basically this car scares the shit of out me on the road.

Anyone with HKS coilovers know which way you turn the knob to adjust the stiffness. I assume turning it counterclockwise is soft and clockwise is stiff. I am on setting 2 of 12 right now i believe. It just makes sense to me that stiffing it would be like turning a screw........righty tighty lefty loosey.

BTW the car is a fully gutted 88 FC with about 315whp. so maybe the weight reduction has screwed me a bit.???

"bouncing" actually happens because of an underdamped suspension (spring too stiff for the damper), so you might actually want to try adjusting the damper to stiffer.

what are the spring rates on those coilovers again? you could try getting some softer springs, which should help.

chances are they are just another typical coilover in that it is really damn stiff, and does not perform well on anything other than smooth surfaces. aftermarket coilovers for the FC don't really have great damping characterisitics, other than being really damn stiff...

make sure you have proper alignment also. coilovers can seem to amplify any alignment errors.

I have not gotten an alignement yet and the factory springs on the HKS hyper is 450 front and rear or 8k in the spec sheet.

I am going to try stiffening the dampers a bit more, but it isnt a bouncing like an oscillation after a bump its more like a bump and the car gets pushed in the air. I would have to guess it feels like the spring rate is higher than the corner weight of the car!!!

HKS apparently doesnt label their springs so I dont know how to test what the spring rate really is, since you can custom order stiffer springs up towards 18k!!!! why?!?

i don't really see the point of an 8/8 rate. that's stiff for the front, and really stiff for the rear. and doesn't seem like a good balance. especially considering that you are, probably, less than 2500lbs if your car is gutted, so yeah, that doesn't help.

if it is not bouncing/oscillating, then your wheels are just loosing contact patch coming off the ground when you hit a bump. just too stiff.

things to do:
- get some softer springs from HKS
- get some different coilovers with better rates and damping (it could be that your dampers are worn also)
- get an alignment (don't use stock settings. get an expert to do it, and they can adjust the alignment based on your current setup. things like camber and toe will affect how the car reacts over rough surfaces and turns).
- put the stock sway bars back on
- don't run lower than 50 profile tires

what type of track use do you do? if you don't go to any road courses or autocross, i see no need to have coilovers with that kind of spring rate if you care about a decent street ride...

My car is actually more around 2200 lbs as of now.
I race road courses a few times a year and auto-x every other weekend.
I would hate to get rid of the hks since they are nice, but def not for my application I believe. I am 99% sure the spring rate is the issue and I would preffer a close rate of 375 Front 300 rear. My tires are a 225 or 235 with a 45 series profile.

You hit the nail on the head I loose traction over bumps. The car is not bouncey at all it hits a bump and then returns to its position but even breaking under normal breaking conditions have induced wheel lock up due to the tire leaving contact with the pavent. A normal stop goes like this....slow..chirp....chirp...slow..etc etc.

The scariest part is when i hit a bump on a turn, it throws the car to the outide of the curve...quite nerveracking..

I have a lot of negative camber in the front and maybe that might cause some issues with not-on the limit cornering due to the contact patch not being 100% available. I think with a suspension like mine, its almost like it isnt working so the car isnot traveling enough suspension wise to allow that tire to roll over to a flat contact patch......arghhhh

Is the ride height set very low? My Tein Ra's acted like this when I set them very low.

the ride height really wont change. The springs are so stiff they dont wanna move alot. The fronts are about 1/4" for their lowest setting and the rears are 1/2 in from their lowest setting.

when I lowered the perches down the car really didnt lower much.
I could try to raise it back up but I dont want that 4x4 look. Maybe I should get a shorter spring that wont have to sit as low on the shock perches. Because even at its lowest thread the springs are still compressed between the perch and upper mount.

8kg/mm spring is not that stiff. i have 8F 7R on my 240sx and its uncomfortable for daily, but it certainly doesn't toss the car around. nor do i lose traction over bumps. i live in jersey... the whole road system here is like one giant pot hole.

it sounds like a damper issue. set it to full left and go for a drive. then set it to full right. see which one feels stiffer. on my coilovers, left is loose, right is tight. adjust accordingly.

you might also try the zip tie on the shock piston. see how far the shock is compressing. all the way to the top = not good. not at all = also not good.

Ditto on the tie wrap. You could be hammering the bump stops from being too low. That's very bad, the spring rate goes up a ton very quickly, which causes a loss of traction.

You don't necessarily need springs from HKS. Depending on the dimensions you should be able to use springs from other coilovers. Eibach makes metric ID springs in most of the common sizes. This would likely be cheaper, and is almost guaranteed to be faster than getting HKS springs. Tein also makes a few different ID's of springs, those might fit.

I've heard of lots of people running as stiff as you or stiffer without similiar issues, so there's probably something wrong, my first guess is that you're too low and are hitting the bump stops.

definetly 8kg/mm, even 9kg/mm, people are running without huge problems on the street. in the front i think it is pretty stiff for a 2200lb car but is ok, and i think the rear you want to be running softer rate.
and yes, you don't have to get springs from HKS.

in any case, as mentioned people have run stiff rates without these sort of crazy issues.
raise the vehicle height so it is not too low. and inspect the dampers to see if any of them are damaged.

I am going to try my roomates ground control springs to see how that helps.

here is my ride height.
http://www.imagestation.com/picture/...9/ee42903e.jpg

that does look quite low. it could be possible you are hitting the bump stop in certain instances.
raise it back up at least an inch and see if that helps at all.

Please stop comparing different vehicles...
You cannot offer any applicable data unless we're talking about the same car.


-Ted

I'll agree with RETed in general on that point, but with the 240SX and the FC, they've both got struts in front and they weigh about the same, so for a harshness comparison it's quite valid. The rear suspensions, while different, seem to work with similiar spring rates too.

Yep, MacPherson struts up front, but suspension (and steering) geometries are totally different.
Drive both and you're understand how different they feel.
240SX runs tension rods all over the damn place!


-Ted

i think you said your car is lowered all the way? it sounds to me like you are hitting your bump stops. i have tein flex's (7k F, 5k R) and they arent too stiff at all. driving very fast on a local mountain road thats bumpy, the car bounces up and down a lot with the contour of the pavement, but stays on course with no trouble (doesnt lose contact over bumps under hard cornering). so yah- i say try raising your car and stiffening your shocks. hitting the bump stops will make the car go nuts regardless of suspension settings.

yup. if you hit the bump stop (suspension runs out of stroke/travel) you are basically having an infinite spring rate...well, not infinite. but really damn high!
have you tried increasing the ride height to see if that makes a difference?

i drive FC's quite often. indeed the 240sx and FC have a very different driving feel. we do have tension rods front and rear. and my eyes do glaze over when i look at diagrams for the FC's rear suspension.

at any rate, a 6-8 kg/mm spring rate is nothing new for FCs. many coilovers slap on a cookie-cutter rates like 6/4, 8/6 etc. it certainly shouldn't bounce him so hard his feet come off the pedals and his tires chirp while braking over slightly uneven pavement.

kind of moot after the pic anyway. car definitely looks too low. probably hitting.

I agree.
hIGGI runs the same type of damper system, and he says it's not that bad.
I suspect the dampers are no good.


-Ted

well the shocks arent leaking and there is no oscilation of the ride, so I believe the dampers are doing their job. Ihavent had a chance to raise up the car but I am going up about 1 inch to see what happens.

I also read that some of the japanese HKS 12 way adjustables like mine came with a 10k F 9k R setup.

Once I raise it up Ill report back.

BTW is there any other way to tell of a bad shock, since it doesnt leak and it doesnt oscillate over bumps...thats sounds like a good damper to me.

You hold your breath every time you park that thing, or drive near a curb, don't you?

That picture is of your car under corner load. That does NOT represent your static ride height. It certainly doesn't look like it is overly stiff, with the amount of body roll you have, and I have driven cars much lower than that without any issues.

I think in this case, it is more of the driver that needs to make adjustments, moreso than the car.

On top of this, the higher springrates are necessary when you are lowering your car that far, as you are putting more force on the coilover itself, due to the change in roll center.

Drive the car more. If you got into a JGTC car right now, you would think it was the worst car in the world... but it takes an experienced driver to extract the most from the "tuned" suspension.

Try fitting some better wheels/tires under there, that will help more than I could ever say enough about. It looks like you have some narrow wheels, and narrow tires... Both not very good for maintaining a solid CONTACT PATCH. Nothing else is more important.

I understand what you are trying to say, but don't insult my driving. The body roll in the picture is from turning a 180 at the end of a straight I was doing about 55-60 entering a U-turn.

So you are saying when I am going 60mph and hit a bump or expansion gap my car goes air borne then thats OK?? It is blaitenly obvious that the suspension is too stiff for my application.

Yes, there are other ways for the shock to fail without leaking externally.
Quick-n-dirty is the "bounce test", but with those high spring rates, this might be next to impossible.


-Ted

yeah, i have that problem because my stock shocks are nearing their 21st birthday