TarHeel085 said:
so who has some input on what rate coil to go with, since i cant afford to be out $68 by gettin the wrong coil, which are non-returnable. and also, where should i put my front link mount? as previously mentioned, i was leaning towards the rear mount for the lower control arm. ANY input would be much appreciated!
I guess you can calculate the proper spring rate assuming you know about how much weight each wheel holds up (subtract about 100 lbs because the wheel is unsprung weight, along with some suspension components). You already know the total distance the shock travels and I'm assuming you probably want the shock to be half compressed at ride height. So just go with the F=kx equation (dont pestor me about the negative sign, no vectors here
you know which way is up and which way is down). Take X as half the compressed length and F as the weight at each wheel (minus that 100 lbs or so) - that'll give you K which would be the spring rate.
BTW Just to let you know, the FOX shocks typically come with alluminum bushings at each eye already. So you don't need to put spacers or more bushings on them.
I understand you're doing coil-overs but I still dont undestand some of the terms - like kicker bar
I'm so new!
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EDIT: I'm going to
TRY (key word
) explain the spring rate thing for future readers following the same conversion. If anyone finds a problem with my explanation, pleas let me know so I can change it.
F = -kx
This equation is based on Hooke's law (http://en.wikipedia.org/wiki/Hooke's_law) which accurately describes deformations of materials and the resistance (force) to such deformations. Some of us may remember this dandy equation from high school.
So to break the equation down:
F represents the force
k represents the spring rate/constant
x represents the degree of deformation
We'll ignore the negative sign for now because, in terms of springs in vehicles, we know which way the spring will apply the force. Soo getting rid of the negative sign:
F = kx
In terms of coil springs (or any linear spring for that matter), we can predict about what the spring rate would be given that we know the two other variables (there are three variables in the equation, we want to know one of them, so we have to know the other two). But first lets rewrite the equation just to make it a little easier with the things we want to know on one side and the things we SHOULD know on the other side. Sooo, moving X over to the left, we see that:
k = F/x
Well now that we have what we want to know on the left (k) and what we SHOULD know on the right (F and x), we need to make sure we understand exactly what F and x are within the context of coil springs on vehicles.
F represents the Force that this spring will apply to suspend the vehicle at the proper height. Of course, looking at the original equation and from everyday knowledge, springs do not apply a contant force - they push back more and more as they are compressed more and more. But in terms of vehicle weight, there is only one Force and that is the weight of the vehicle due to gravity on flat ground sitting still. To narrow this down more, since this coil spring will suspend the front axle, this F represents how much weight is at each front wheel. I mentioned earlier to subtract 100 lbs or so because the wheel, the tire, and some suspension compnents will not be 'suspended' by the coil spring - these components are on the opposite side of the coil spring from where most of the vehicle's weight is being applied.
x is how compressed the spring will be at ride height. The good thing about this is that, because TarHeel is using a coil over setup, we know exactly how much travel this spring will be allowed - which is the stroke length of the coil over's shaft (5.10" - lets assume 5.0" for simplicity). Another assumption we have to make is that the coil over will be about half compressed when the vehicle is sitting still on flat ground - so lets say the coil-over assembly will be compressed 2.5". Well wow there then is our x term!
So now we know (or SHOULD know) everything on the right side. We can (I guess) appoximate how much weight is at each wheel and subtract 100 lbs or so from that to give us the F term. We also already know the x term by knowing the total shock stroke length and also making an assumption that, at ride height, the coil over will be about half compressed.
Just to give an example, lets say that the Explorer Sport at hand weighs 3,750 lbs and that 70% of the weight is at the front wheel. So thats about 2,625 lbs total at the front wheels which means 1,300 lbs at each front wheel and minus 100 lbs or so, that gives us 1,200 lbs. Using the same coil over with 5" of travel, and 2.5" compressed at ride height, the equation becomes
k = F/x
k = 1200 lbs / 2.5 inches
k = 480 lbs/inch
Which sounds about right for such a heavy vehicle. Heavier track cars (Mustangs) on twisty courses typically run about 650 lbs/inch - but those are cars probably have less suspension travel which means greater spring rate.
But wait! We're not done yet. Another assumption we made is that this coil-over spring rate will be sitting perfectly vertical. Most likely, it will be angled at some degree from the vertical. Most of the times these angles are small enough so that you don't need to worry too much about them - but just in case, the equation you need to use to figure out the spring rate k2 for a shock that is at an angle A is:
k2 = k / cos (A)
Where again, A is the angle of the spring from the vertical in degrees (not radians) and k is the spring rate we figured out above with the k = F/x equatoin.
So just to get an idea of how an angle changes our spring rate, lets take that same 480 lbs/in spring rate and run it at a 5 degree angle.
k2 = k / cos (A)
k2 = 480 / cos (5)
k2 = 481.83 lbs/ inch
So you can see the angle affects it but not by much.
If you're unsure between two rates, I would opt for the higher spring rate just because most people prefer a stiffer ride than one that feels like a battle ship in a tsunami.
AGAIN, I'd like to point out that we made an assumption on how much weight there is at each front wheel -- this is the hardest part!
