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Originally Posted by skets
well for the drop (1.5") the spring rate of the tein h-tech are pretty low as in teh fronts are not even 250 and they are progressive rate springs .. and all the info i've seen here indicates that you need a rate closer to 300. So i find it strange that these springs work so well.
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I think the issue here is really that people don't know how "drop" correlates to the probability of bottoming out, and you're tired of having to guess. If that's the case, I have a general rule of thumb that I sometimes use for maintaining sufficient travel in street cars. Here's how it works:
As you know, springs compress when you apply load to them. The more load you apply, the more a spring compresses. With a linear rate spring, the amount the spring compresses relates directly to the amount of load you apply to it. Here's the relationship between all of those factors with a linear rate spring:
(Applied Load) / (Spring Rate) = (Distance the spring compresses).
So if you know the spring rate of the stock springs and the amount of travel the stock suspension has when the car is parked, you can calculate the amount of load that one corner of your car can handle without bottoming out:
[Amount of load you can apply] / [Stock Spring Rate] = [Stock Damper Travel]
or:
[Amount of load you can apply] = [Stock Damper Travel] * [Stock Spring Rate].
For example, if I know that my stock front dampers have 3.75 in of travel and that my front springs have a spring rate of around 125 lb(f)/in, I can stick that into the above formula and figure out that I can put a maximum of 468.75 lb(f) of load onto that corner before it bottoms out:
[Amount of load I can apply to one stock front damper] = 3.75 in * 125 lb(f)/in = 468.75 lb(f).
Now, what I like to do is to
try to keep the maximum amount of load I can apply the same before and after lowering springs are installed (<< this is my rule of thumb).
If you buy lowering springs and put them on non-shortened dampers, you know exactly how much it's going to reduce your travel by (the amount of "drop" advertised = amount of travel you're going to lose). So you subtract that amount from the stock damper travel, and come up with a similar formula for after you install lowering springs:
[Amount of load I can apply to one stock front damper] = ([Stock Damper Travel] - [The Advertised "Drop"] ) * [Minimum Spring Rate of the New Spring].
or:
[Minimum Spring Rate of the New Spring] = [Amount of load I can apply to one stock front damper] / ([Stock Damper Travel] - [The Advertised "Drop"]).
This formula will tell you what the spring rate of the lowering spring needs to be in order for you to keep the same maximum load capacity on that corner of your car.
Say that I want to lower the car in the example above 2" with KYB AGX's (non-shortened aftermarket dampers). If we plug in the numbers, we get this:
[Minimum Spring Rate of the New Spring] = (468.75 lb(f)/in)/(3.75 in - 2 in)
[Minimum Spring Rate of the New Spring] = (468.75 lb(f)/in)/(1.75 in)
[Minimum Spring Rate of the New Spring] = 267.85 lb(f)/in
This tells us that in order to lower the front of the car 2" and still maintain the same maximum load capacity as stock, we'd need to make the spring rate of the lowering spring at least 268 lb(f)/in.
Now I'm going to warn you by saying that the above will only give you a
conservative estimate of how stiff your lowering springs need to be to avoid constant bottoming out. Factors like the increased compression damping you get with aftermarket dampers and the decrease in load transfer associated with stiffer springs will all affect the actual outcome and throw off the estimate by some amount. The only reason I'm posting this is because it's a very simple formula that people can apply when they're choosing lowering springs, and the numbers it produces will always be
conservative estimates.
If you follow this rule when choosing linear rate lowering springs, you should not encounter severe bottoming problems.
That's my rule of thumb. I hope it helped a little and not just confused a lot.
Linear Mode
