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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 10:04 pm 
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Location: Reno, Nv
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i still feel that the critical factor in choosing springs is knowing how much a spring is loaded to at ride hight then work back to the fully extended hight, if you only have a given length for the coilover assembly and ride hight is at the mid point, then you will know what you are stuck with for NF wether you like it or not.

There is more than one way to determine the correct spring rate. A person does not have to "work back to the fully extended height" as an example if the spring has 300 lb on it at ride height with the suspension compressed 3 inches you could use a 100 lb/in. spring.
Or 50 lb/in that is preloaded 3 inches.
Or a 300 lb/in spring that is compressed 1 inch so that with the suspension is fully extended (full drop) there will be a 2 inch gap between the spring and the spring seat that should be filled with a tender spring. So any (almost any) NF could be accommodated.

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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 10:09 pm 
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Yeah, rear travel sucks. But you're right, I did mean 2" of compression travel, not full travel. It's generally accepted as a good idea to have more rebound travel than compression travel, but I don't think you can get away with that in a Locost, at least in back.

Also, my choice of 2 Hz for the rear is just that, my choice. There is no ideal value, it's just a question of how often you want to bottom out. You can probably go with a 1.5 Hz spring and be fine on relatively smooth roads. You'll put up with more bottoming on rough roads than you would in my car, but in regular driving at least your fillings won't fall out.


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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 11:29 pm 
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john hennessy wrote:
the spring fixtures at each end of the spring, that being the chassis at one end and the "a" arm at the other, would move equally when the spring was compressed by a bump in the road and the chassis would dip down the same amount as the wheel moves up, but what appears tto happen is that the end of the spring on the "a" arm moves up and the center of the spring moves up half of that
All motion is relative such that what you see as stationary is moving in another frame of reference, and what you see as moving is stationary in another frame of reference. A spring only cares about its own perspective. So as you so observantly noted already, if only one end of the spring appears to move the middle of the spring moves half as far. Thus if you measure from the middle of the spring, both ends of the spring did move an equal distance.



nick47 wrote:
If unsprung weight were somehow zero, the body wouldn't move at all, and the suspension would completely absorb the bump. Occupants of the car wouldn't feel a thing...
Actually unsprung weight is only part of the equation. A theoretical car with zero unsprung weight would most certainly have body movement and the occupants would still absolutely feel it. An overly simplified example would be to consider a car with 300lb/in springs supporting the sprung weight and zero unsprung weight. If the car hits a bump that compresses the spring by 1 inch, the spring would still be transmitting 300lb of force up to the chassis. You are correct that unsprung weight and unsprung vs sprung ratio does play a significant role, since the spring (and shock) must also control the momentum of the 75+lb being thrust upward by the bump in the road.



john hennessy wrote:
my current setting are 1.6 in the front and 1.8 in the rear
Those sound like your method also worked well in bringing you to some pretty reasonable numbers. :cheers:

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 Post subject: Re: Coil over suppliers?
PostPosted: December 14, 2012, 12:16 am 
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Driven5 wrote:
A theoretical car with zero unsprung weight would most certainly have body movement and the occupants would still absolutely feel it.


You're right. Because bumps typically have some contour to them, in a 2-inch bump at 50 mph, the corner of a car with massless wheels, tires, control arms and springs would move upwards about 0.03". You might feel that, but I probably wouldn't.


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 Post subject: Re: Coil over suppliers?
PostPosted: December 29, 2012, 1:16 pm 
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JackMcCornack wrote:
JPS Europa wrote:
HeHe....I hear you.
We had expected 1-2 weeks when I placed the order. It ended up being more like 2 months. They blamed it on racing season.
And Nick noted...
nick47 wrote:
I've always had a real problem with that excuse. Like the racing season came up unexpectedly.
With umptyjillion combinations of shock lengths, spring weights, balls/bushings and even shock body material, neither Dennis or I stock these coilovers in advance. What we do have is a toe in the door at the GAZ factory, and Dennis' and my combined orders do give us some clout regarding haste, but every GAZ order is a custom order and I don't think they treat racing season like WalMart treats the Christmas season--they don't hire and lay off staff with the ebb and flow of seasonal orders.

And now and then they goof with their predictions. For example, GAZ doesn't wind its own springs and a delivery delay on some common weights was the source of one recent delay...perhaps that one was palmed off as a "racing season" issue, but I assure you that neither I nor Dennis have delayed getting orders processed because it was racing season.

I think what we've got is the fastest way to get GAZ shocks to your door. GAZ trusts Dennis (the US distributor), Dennis trusts me, and I trust you, and an order placed with Kinetic is in process at GAZ the following day...and when completed, it's FedExed to you direct from the factory.


Thanks JPS/Jack, goodness knows I have no one to blame for any delays but my self. Should have had these ordered months ago, but life finally got in the way.

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 Post subject: Re: Coil over suppliers?
PostPosted: January 4, 2013, 8:49 pm 
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nick47 wrote:
You're right. Because bumps typically have some contour to them, in a 2-inch bump at 50 mph, the corner of a car with massless wheels, tires, control arms and springs would move upwards about 0.03".


Seems to me that would depend entirely on the spring rate.

Where did you get .03?

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 Post subject: Re: Coil over suppliers?
PostPosted: January 5, 2013, 4:16 pm 
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You're right. It does depend on the spring rate, and the weight of the car. I used a 1000#-rate spring to simplify the math.

The .03" was a rough estimate based on a few generalizations. The math was greatly simplified by having zero mass in the unsprung bits. If you do the calculations with a more normal spring rate of, say, 200#, then movement would be reduced even further.

Justin and I had a good discussion about this afterwards, and he pointed out quite correctly that it's not the movement that the occupants feel, but the acceleration. In a 2" bump, a massless 200# spring will compress 2", creating an upward force on that corner of the car of 400 lbs. If that corner of the car also weighs 400 lbs., acceleration upward is 1g (32 ft./sec./sec.).

However, because the spring and unsprung bits are massless, they can accelerate infinitely fast, and so the bump is over for the suspension in less than .005 seconds, depending on the width of the bump. So 1g of acceleration will move the car at most 32*.005*.005/2 feet, or .0004 feet, which is .0048". Of course the 1g is an instantaneous max, so we've really oversimplified things by saying the car would feel 1g for .005 seconds. It wouldn't of course, so movement and mean acceleration would be a lot less. Both Justin and I had to admit we didn't know enough about the human nervous system to say definitively whether or not the occupants would be able to feel that.


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 Post subject: Re: Coil over suppliers?
PostPosted: January 9, 2013, 12:53 pm 
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Actually it's not even acceleration we feel, it's the rate of change of acceleration, called jerk; gravity is a constant 1 g field, and notice how at takeoff you stop noticing the acceleration after the turbines have spun up to full thrust.

Also you're placing undue significance on the effects of zero unsprung mass.

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 Post subject: Re: Coil over suppliers?
PostPosted: January 9, 2013, 1:02 pm 
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In the days after Dale Earnhardt Sr's death, Ford Motor Company crashed a NASCAR chassis into a wall at roughly the same speed of the into-the-wall vector of Dale's crash (roughly 42 mph into the wall). IN the words of the engineer, "They killed the dummy." As he explained it, the problem wasn't the total amount of energy under the curves, but rather something called the "impact spike".

Which, I assume, is that "change of acceleration" that was just mentioned? That the NVH (noise, vibration, harsheness) is really the impact spikes in many cases (along with harmonic vibrations and other stuff)?

BTW, if you haven't read it yet, I just got done with Steve Olvey's book, "Rapid Response: My inside story as a motor racing life-saver". Totally worth the read. Totally. Scary how bad emergency medicine used to be, even at major motorsports events.

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 Post subject: Re: Coil over suppliers?
PostPosted: January 9, 2013, 7:00 pm 
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NoahKatz wrote:
Also you're placing undue significance on the effects of zero unsprung mass.


We're not placing any significance on the effects of zero unsprung mass. We're just saying the less unsprung mass, the better.

And of course we can feel acceleration. If we couldn't, why would any of us want 300 horsepower?


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 Post subject: Re: Coil over suppliers?
PostPosted: January 11, 2013, 12:43 am 
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nick47 wrote:
NoahKatz wrote:
We're not placing any significance on the effects of zero unsprung mass. We're just saying the less unsprung mass, the better.


Then why keep mentioning it?

More power gives more jerk.

Did you not understand the plane example?

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 Post subject: Re: Coil over suppliers?
PostPosted: January 11, 2013, 1:24 am 
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NoahKatz I don't think the plane example is a good one as the acceleration is very high at takeoff an then reduces to zero at a slow rate normally. Acceleration is the rate at which the velocity of a body changes with time. It is easier to feel spikes of acceleration but a constant acceleration can also be felt that's what forces us back in the seat when the loud peddle is pushed, and I might say pushes us against the seat belts with the brakes applied.

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 Post subject: Re: Coil over suppliers?
PostPosted: January 11, 2013, 1:28 am 
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NoahKatz wrote:
Then why keep mentioning it?

To be honest, it was because I thought you didn't understand what we were talking about. I'll refrain from discussing it any further.


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 Post subject: Re: Coil over suppliers?
PostPosted: January 14, 2013, 11:19 pm 
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MYTF wrote:
NoahKatz I don't think the plane example is a good one as the acceleration is very high at takeoff an then reduces to zero


Yes, but if you notice it stays high for a few seconds after reaching full acceleration, but it's ho hum compared to when the turbines are spooling up and the acceleration is increasing.

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 Post subject: Re: Coil over suppliers?
PostPosted: January 14, 2013, 11:21 pm 
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nick47 wrote:
To be honest, it was because I thought you didn't understand what we were talking about. I'll refrain from discussing it any further.


How's that? You said "massless" before I said anything.

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