Spring Preload

[AGlobalThreat]

I have tried 4 different preload settings in the rear but still cannot get rid of the bounce from the rear whenever I go over any part of the road that isn't perfectly flat. It feels like the shock isn't absorbing the bump at all, it transfers to the chassis and throws me up and down in my seat. I have tried setting the preload with the spring snug but not tightened extra, and also tried with the spring tightened 1/8" and in between 1/8" and 1/4", and 1/4".

Another thing that confuses me is why the passenger side rear sits so much higher than the driver's side rear. I would think that the passenger side would be somewhat heavier since most of the gas is over there and theres seems to be almost no weight on the other side, but I have to shorten the coilover on the passenger side by quite a bit to get the rear to sit even (With the spring preload identical in the rear L/R).

Any tips/techniques to help me with the rear coilovers? I have not adjusted the damping yet, was trying to figure out the proper preload settings first but am unable to find the best amount of preload and am unable to get rid of the bounce I get from the rear whenever the road isn't flat.

My supra is about as light as it gets without tubbing the chassis and it's on D2 coilovers, I was told the spring rates are 17.8F and 8.7R.

Any and all help is appreciated, TIA
Craig

 

[IJ.]

You need to adjust rebound damping

ALL cars are rarely perfectly square due to production tolerences so a lot of times you will need to adjust corners to make it sit flat.

Keep in mind most times a car will only have a driver so may require more preload on the drivers rear to offset your weight.

 

[AGlobalThreat]

Do you have any recommendation for what I should set the preload to before adjusting the damping? I was already planning on making the damping pretty soft so the car will be able to squat more and get more traction (Already running without a front sway bar, front suspension is all dialed in and rides great, height is perfect). Right now there is 1/8" of preload on both rear springs.

I only weigh 128 lbs so I don't make that big of a difference in the car, should I just give the rear passenger side another half turn of preload?

I tried reading sites online about how preload works but never got a clear understanding. If the spring is linear, how does preload affect the spring besides the obvious length of the compression travel?

Thanks for the reply! <3

 

[Wiisass]

Don't even worry about preload. There's really no reason for you to worry about it besides making sure it's equal.

I would just put a little in or just enough to keep the spring seated and then set the height using the lower mount.

If you're having trouble getting the height even, are you messing with the secondary height adjustment or just the preload? Like IJ said, cars aren't always even, so it might not be perfect.

And the bounce, it probably won't go away, ever. Or at least until you ditch the D2's and get good shocks. But the bouncing could be a result of a lot of different things. Tires, spring rates, valving, etc.

 

[IJ.]

The biggest + of aftermarket Coilovers is also their biggest -, they're so adjustable.

Unless you fully understand what each setting does and how it interacts with the vehicle dynamics it's far too easy to lose your way.

You need to baseline the car then discuss what you'd like it to do differently then change 1 thing at a time keeping a log of each change you make so it's easy to revert if it's wrong.

 

[AGlobalThreat]

If you're having trouble getting the height even, are you messing with the secondary height adjustment or just the preload? Like IJ said, cars aren't always even, so it might not be perfect.

I'm setting the preload even on both sides and then adjusting the height with the lower mount.

Unless you fully understand what each setting does and how it interacts with the vehicle dynamics it's far too easy to lose your way.

You need to baseline the car then discuss what you'd like it to do differently then change 1 thing at a time keeping a log of each change you make so it's easy to revert if it's wrong.

That's why I'm asking these questions. I'm trying to fine tune the suspension as best I possibly can but it would be much easier if I fully understood exactly what each change is doing.

 

[IJ.]

You need to be methodical and give us some feedback.

Drive the car take notes come back and tell us what it's doing that you like/dislike then we can suggest a change.

repeat

Try and find a nice quiet bit of road close by to use for testing you don't need to drive it 11/10's just consistantly.

 

[AGlobalThreat]

You need to be methodical and give us some feedback.

Drive the car take notes come back and tell us what it's doing that you like/dislike then we can suggest a change.

repeat

Try and find a nice quiet bit of road close by to use for testing you don't need to drive it 11/10's just consistantly.

Everything is fine except for the fact that the rear feels so stiff that it bounces up and down and feels like there is no suspension. The shocks are not absorbing the bumps and it is transferring to the chassis and throwing me up and down in the driver's seat.

 

[IJ.]

Do the shocks have seperate compression and rebound settings?

 

[AGlobalThreat]

No I'm pretty sure it adjusts them at the same time.

 

[AGlobalThreat]

The coilovers are already set to full soft

Would removing the rear sway bar help?

 

[AGlobalThreat]

I want to get my car aligned this week, but am unsure what specs would be best.

I want to get maximum lateral traction, the car squats quite a bit (and will squat even more when I switch out the rear springs), so I need positive camber in the rear correct? So as the rear comes down the tires sit flat and I have the best contact patch.

Should I be changing toe front or rear? Any recommended alignment specs for the front?

I really need some help with this because I am unsure what alignment specs to use.

Any and all help is appreciated

-Craig

 

[LordDigital]

I want to get my car aligned this week, but am unsure what specs would be best.

I want to get maximum lateral traction, the car squats quite a bit (and will squat even more when I switch out the rear springs), so I need positive camber in the rear correct?
-Craig

Positive camber in the rear?? ,could only be good for Drag Racing provided that the car is trailed to the DragStrip

For street CoilOver setup I would go at least negative 1 on front and rear ,maximum (positive) Caster in front with 0 toe ... and total to-in of 1mm for the rear.

 

[Wiisass]

You don't want positive camber ever if the car is meant to turn as well. Under cornering, the loaded corner will lose camber relative to the road from the suspension geometry, so you need enough static camber to still maintain some negative camber relative to the road to produce good grip.

I would do something like -1 to -1.5* camber all around. Get caster even in the front, without arms, you won't have the most adjustability. I would just try and get camber and caster even on both sides and hopefully they will be in a decent spot. I also like a little toe out in the front and a little toe in for the rear. Like 1/16" at each wheel. Just enough that you feel it and not enough to really affect tire wear.

 

[AGlobalThreat]

Thanks a lot for the input guys! I really appreciate it! :icon_bigg