adjusting height/dampening with coilovers

[hjkim483]

I was testing out some settings with my Tein SS and was wondering some physics behind this stuff. Tein tells you to set it at a certain default height (.79 inches from the bottom of the thread) and at certain clicks from the stiffest (8 in the front and 6 in the rear) Now, if you were to raise the car up from this default height (compress the spring more upwards; 1.5 inches from the bottom of the thread) would you want to stiffen your ride more or soften it more, dampening-wise?

I was thinking, since the springs are more compressed and closer to each other, that the dampening should be stiffened more to prevent bottoming out... Am I right in my logic?

How does bottoming out feel like? Do you hear your tires hitting the wheel well?

[DopeCelicaGT]

^^^Mainly, if you adjusted the springs to be more compressed then you might be raising the spring rate, depending on what type of springs you have, and thereby would be increasing the force upon them, making them stiffer, obviously. If you do this then your valving needs to be increased as well to handle the quick forceful rebound of your newly adjusted springs, at least that is what I have been taught. Look at it this way, even though some springs like Hotchkis will work with stock struts its not exactly a good idea because the rates of the springs will cause the springs to rebound much faster than the stock struts can handle, if that makes sense. In order to compensate for the new springs you would want to buy some struts in which either had dampening capabilities or adjusted the dampening automatically, depending on the driving style and input they got from the spings. I hope all of this makes sense. It is kind of like this if you get stiffer springs then you want better valved struts to go along with them. The funny thing is a set up with some fairly soft springs and some struts with an increased rate of valving can actually handle better and feel better than a set- up consisting of stiffer springs and better valved struts. The reason being is that when the suspension is too stiff it can actually make the car bounce over things, nto exactly the best thing in the world. The set-up with soft springs and more aggressive valved struts however would give you good handling characteristics and allow the tire to maintain a good contact patch with the road no matter what the conditions. It is all kind of hard to explain but lets put it this way, it is better to ride on the surface of the road and have the suspension follow that input vs. bouncing over the surface of the road.

[hjkim483]

thanks for the detailed explanation.
So it seems like, since I compressed the springs by pushing them upwards, I would need to stiffen my struts to compensate it. Am I right?

[boostjunkie26]

I think DopeCelicaGT is correct, if we were to talk about a progressive rate spring. However, the spring in that coilover is a linear rate, correct? Therefore, regardless of what position of flex the spring is in, it will always give the same resistance, would it not?

Therefore, if by some act of God, someone were to tighten the perch so as to begin to compress the spring (unless you weld a breaker bar onto the perch, I don't see a person compressing it that much), you will still ultimately realize the same rate as if the spring were not compressed.

Crank the perch all the way up or leave it down. It's the same spring (and rate). That's why companies such as ground control let you swap out spring rates... if you could change it on your own, you wouldn't need their service.

[DopeCelicaGT]

Originally posted by boostjunkie26
I think DopeCelicaGT is correct, if we were to talk about a progressive rate spring. However, the spring in that coilover is a linear rate, correct? Therefore, regardless of what position of flex the spring is in, it will always give the same resistance, would it not?

Therefore, if by some act of God, someone were to tighten the perch so as to begin to compress the spring (unless you weld a breaker bar onto the perch, I don't see a person compressing it that much), you will still ultimately realize the same rate as if the spring were not compressed.

Crank the perch all the way up or leave it down. It's the same spring (and rate). That's why companies such as ground control let you swap out spring rates... if you could change it on your own, you wouldn't need their service.

Exactly, my response was in regards to a progressive rate spring, not linear rate. If the spring is in fact a linear rate spring then boostjunkie is 100% correct most coilover springs that I have seen are linear rate. However, the only thing I do not get is if the rates of the springs on even a linear spring did not change with compression then why do manufacturers recommend you to set them to a certain height? Also, my TRD coilovers have linear rate springs and there is a big difference on the handling characteristics of the car when the spring is more compressed vs. being uncompressed or not compressed as much, if that makes sense.

Justin

[boostjunkie26]

Originally posted by DopeCelicaGT
However, the only thing I do not get is if the rates of the springs on even a linear spring did not change with compression then why do manufacturers recommend you to set them to a certain height?

I think this has more to do with roll centers, king pin angles, and camber, castor, and toe (bump steer) changes. The celica's suspension is designed with a given bump characteristic, for the stock spring rate. As the spring rate is increased, the amount the suspension will deflect will change. Most notably less deflection for an increase in spring rate. Therefore, the manufacturers set "recommended" heights, which place keep the suspension within its "sweet spot," even though travel is decreased.

I have a feeling if you change the spring rates of these coilover systems drastically, that the manufacturer would recommend a different ride height.

Originally posted by DopeCelicaGT
Also, my TRD coilovers have linear rate springs and there is a big difference on the handling characteristics of the car when the spring is more compressed vs. being uncompressed or not compressed as much, if that makes sense.

Most likely due to the action of the dampers, rather than the springs. Perhaps the location of the piston within the bore will affect its dampening characteristics. If it's a gas charged damper, the piston's location in the bore might be even more affected.

But that's just a guess.

[MicaCeli]

Tein gives you the settings because those are the setting that give you the 'optimal' weight distribution and ride height.

It doesn't matter how high you crank the perch, once you lower the car the spring will compress.....and like boost said they are linear rate springs so it doesn't matter where they are they will give off the same resistance.