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 Post subject: Re: Coil over suppliers?
PostPosted: December 12, 2012, 1:48 pm 
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john hennessy wrote:
if you know your corner weights, two sets of bathroom scales with a plank between them for each wheel, and an average of their readings will do for most as a base line at each wheel.
then work out the ratio of your "a"arms, the center of the tire footprint to the inner pivot compaired to the shock mounting to the inner pivot.
then the angle of inclination from vertical, vertical being 100% and horizontal being 0% to give the effectiveness of the spring at ride hight.
now the amount that the spring/shock is compressed in inches from fully extended to ride hight and work back to an unloaded spring in inches per lb.
The critical piece of information missing from this explanation is how to understand and choose the desired number of inches of free spring compression at ride height used in the calculation, as by the described method of determining spring rates that is what determines how hard or soft the suspension (ride) will actually be.

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 Post subject: Re: Coil over suppliers?
PostPosted: December 12, 2012, 2:07 pm 
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john hennessy wrote:
remember that a 100lb per inch spring is for the first inch of compression so if they are compressed at ride hight to three inches they are 300 lb springs supporting the car and so on until coil bind.

does anyone else find this concept confusing or hard to grasp (?)


They won't be "300 lb springs" at coil bind since they won't compress further with a 300 lb force. At coil bind they will be supporting 300+ lbs.

Your method of spring definition is certainly confusing. I suggest you describe springs as the rest of the world does; force/deflection. That's the only way spring/suspension calcs can be performed.


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 Post subject: Re: Coil over suppliers?
PostPosted: December 12, 2012, 9:51 pm 
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perhaps either of the two gentlemen cold offer the "correct" advice

i have removed my comments as it would appear that i have no clue what the heck i'm talking about.

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Last edited by john hennessy on December 12, 2012, 10:13 pm, edited 1 time in total.

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 Post subject: Re: Coil over suppliers?
PostPosted: December 12, 2012, 10:00 pm 
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i am wating with interest and i will make no comments about what you say, just get on and explain it so we all know all there is to know about springs.

i have one question though, how does a spring know which end to move so that the wheel goes up instead of the car going down?

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 Post subject: Re: Coil over suppliers?
PostPosted: December 12, 2012, 11:42 pm 
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JPS Europa wrote:
I got my Gaz units from Jack at Kinetic who really just passed it off to Dennis, whom I ended up dealing with...both very pleasant guys. It all took a bit longer than we all thought to ship them and the rear springs were slightly harder than what I spec'ed out, but all in all a relatively painless transaction.
Paul

I will be following this path so, Just curious, how long was a bit longer?

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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 3:50 am 
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john hennessy wrote:
perhaps either of the two gentlemen cold offer the "correct" advice

i have removed my comments as it would appear that i have no clue what the heck i'm talking about.
While some of your comments may have been not very clearly stated, or may have had a few technical inaccuracies, the message you were attempting to convey was entirely legitimate. In fact, whenever I actually get to that point I will probably be following a somewhat similar method to what you described for selecting my spring rates as well. However since I don't have any gut feel as to what compressing the spring 3 inches at ride height means in terms of a ride rate, I will be using the directly correlated natural frequency. This is simply because I do personally do have a gut feel as to what different frequency values roughly mean in terms of ride rate, and is the measure I believe to be the most easily learned as a common language for the purposes of discussion. This is most commonly measured in either cycles per minute (cpm) or Hertz/cycles per second (Hz)...I suppose you could call it cps, but you might get some funny looks from strangers when you do. Generally speaking, I would guess most people building cars on this site will probably be looking in the 1.5-2.5 Hz range, with more street oriented on the lower end and more track oriented on the higher end.

john hennessy wrote:
i have one question though, how does a spring know which end to move so that the wheel goes up instead of the car going down?
From the cars frame of reference the wheel is going up, but from the wheels frame of reference the car is coming down. That's one of the great things about a spring: Since any force applied really just passes right through it, both sides are simply exerting the same force in opposite directions.

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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 9:59 am 
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cboettch wrote:
I will be following this path so, Just curious, how long was a bit longer?

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.

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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 12:29 pm 
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I've always had a real problem with that excuse. Like the racing season came up unexpectedly.


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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 1:02 pm 
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Justin, thankyou for your response,

if what you say is true,

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

if you drop the car from a great hight, what happens then, the chassis goes down so clearly it is able to do so, why does this not happen when you hit a bump on one wheel, i was always taught that a spring that is collapsing has no force to support anything, as in rear axle tramp where if the body is moving down, the axle is free to move up and traction is lost, therefore if the wheel is moving up, the body is free to move down, but it doesn't seem to do that, just the wheel moves up

the reason i ask is not to be difficult, but i have always wondered about cars with the springs mounted across the car as in Airframe fixer's LMP car where the front suspension moves up but does the car dip in that corner, after all the other three corners are at equilibrium balanced on there springs and suddenly that spring is collapsing.

i have seen FWD cars with a damaged rear shock going down the road and that wheel is actually flaping up and down at quite a rate, to the point where the wheel comes off the ground but the corner of the car stays level

just curiouse,

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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 1:52 pm 
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The wheel goes up and the car goes down in proportion to the sprung and unsprung weight of that corner of the car.

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, and the other good news is that the wheel would follow the road exactly, with no loss of traction. The lighter the unsprung weight, the closer you get to that ideal.

Of course one way to improve the sprung/unsprung ratio is to make the car (sprung weight) heavier, which is why a big sedan with blown shocks can seem to be absorbing bumps without the car moving at all.


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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 4:32 pm 
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JPS Europa wrote:
cboettch wrote:
I will be following this path so, Just curious, how long was a bit longer?

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.

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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 4:46 pm 
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Don't worry, Jack, I'm not blaming you or Dennis at all. I'm totally blaming GAZ. Shocks are in the Locost budget for February and we'd like to be driving the car in April. Hopefully that won't be racing season somewhere. :D


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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 5:26 pm 
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nick47,

so what you are saying is that because the wheel/ hub is lighter than the car, it moves first and by moving, then the bump is absorbed thus no further shock travels to the body which being heavy, requires longer to react to the bump, so long in fact that it's all over before it starts.

have i got it now?

so would this provide a need for using the softest springs that will support the car, allowing the suspension to react quickly but stiff enough to stop it bottoming out?

sorry but this raises another question, how stiff does it need to be before bottoming out occures on the adverage locost for most practical bumps you might encounter?

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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 6:50 pm 
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In the zero-unsprung-weight scenario, that's true. However, because there's always some unsprung weight, some of the spring's movement is going to be transmitted to the chassis. In any case I wouldn't let your sprung/unsprung weight ratio determine how soft your springs are. Lighter unsprung weight will improve the ride and road-holding of any spring rate, so it's always good. As for spring rates, I agree with Driven about going for a specific NF within the constraints of your wheel travel.

On the average live-axle Locost, for example mine, you've got roughly 2" of travel in back and about 4" in front. To minimize bottoming out in back, which is much more likely than up front, you're probably going to need an NF around 2.0. You want the front NF to be around the same or a little less, so around 1.75. You can calculate your spring rates from that if you know your sprung weight and motion ratios. Of course you can always go with higher rates than that, particularly if you want to minimize camber change in front.


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 Post subject: Re: Coil over suppliers?
PostPosted: December 13, 2012, 7:39 pm 
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think my fillings would fall out at an NF of anything over 2Hz.

when you say 2" of travel in the back, is that total travel or the ride hight from completely extended

if it is total travel and the spring/shock was about half way extended at 1", that would work out at arround 3.1, bits would fall off the car i think.

if that was the compression at ride hight, 2", that would work out at around 2.2, would be a little stiff for me

now for very slight changes in ride hight, the Hz change dramatically, 0.25 of an inch changes the figure by quite a lot,

my current setting are 1.6 in the front and 1.8 in the rear, and although i do not have any anti roll bar in the front, body roll is minimal, just enough to get camber changes, however i do have one in the rear, specifically to limit the rate of rear body roll and the camber changes.

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.

if you have such a short amount of compression available, then that is all you have and aiming for a nice figure of NF may not be feasable without making provision for a longer unit.

note that most locosts have a falling rate spring setup in the front anyway necesitating a higher spring rate to prevnt bottoming, and an "a" arm ratio of almost 2-1, compounded by laying the spring over requiring even stiffer springs, and you are obsessed with an NF number?

in an ideal world we could have desert racing shocks and springs 2 feet long under our cars but we don't and even then in that situation, they run two different spring rates on one shock and the NF only applies to the lighter one because the stiff one is usually fully extended at ride hight.

and talking of desert racers, how do you have a low unsprung weight with those big tires and wheels?

on a haynes roadster the rear shocks are mounted on top of the rear upright, likewise on a live axle book car, this all limis the length of the spring and there is not much you can do about it without redesigning the chassis.

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