Auto news on Youtube Feb 21 2018

Hello everybody! Bill here from QA1 and today I want to talk to you about a very

popular topic that we get a lot of phone calls on, is "How do I know what spring

rate I need?" There's a couple of different methods to do it. You can get

your car weighed on some corner scales like what we've got over here, we've got

a set of scales. It'll weigh each corner of the car individually. You can use that

number to determine what kind of spring rates you need. The other way to tell is

if you have a spring that you have, that you know what it is. For example, this is

a 14HT150 which means it's a 14 inch free length, 150 pound per inch spring rate.

If you can see how far that spring is compressing, we can very easily

determine how much force is on the car. What works really well about that is

that that takes into account any sort of shock angle that you've got. It takes

into account it doesn't measure your unsprung mass, which is your weight of

your wheels, your tires, your brakes, your control arms all that stuff.

It's just looking at what force is on the spring. So if this particular spring,

which again is a 14HT150, if that were on the back of a car and we measured it

out and it was coming down to 11 inches, that would mean that it's compressing

three inches. From our spring rate video, if you haven't seen it you can check it out,

We know that spring rate is measured by

how much force it takes to compress the spring one inch. So if we know our spring

is compressing three inches from its free length and we know that it's 150

pounds per inch, that tells us right there that that particular spring has

450 pounds of force on it. That's just a multiplication of three inches of

compression times the spring rate which is 150 pounds per inch. Generally we want

to shoot for somewhere between 25 and 35 percent of the free length to be

compressed with the weight of the car on it. So that's going to change for your

front and your rear depending on what style suspension it is. If it's an

independent it's gonna be a higher spring rate than a solid axle.

But we want to see it compressing, and there is a range there because

different springs will work for different things. There's not one perfect

spring that's going to make your car work and every other spring is going to

be junk. There's a range of springs that will work for different applications so

don't get too caught up on what is my absolute perfect spring rate. Especially

if you're looking at between, you know, like a 150 and a 170. They're only one

step apart so the change is not that huge. They will both work for your

car, they'll just work slightly different. Stiffer spring rate will handle slightly

tighter on the street. Softer spring rate will transfer weight side to side or

front to back a little bit easier, it'll also ride a little softer so you can

tailor your spring rate for different applications. And again what we're

shooting for is 25 to 30 percent of the free length to be compressed under the

weight of the car. If you do have, or if you don't have a set of springs that you

know what they are, you can use a set of corner scales. You just look at what the

weight of each corner is. The one thing you got to remember there though is that

that does weigh all of your unsprung mass. So it's gonna weigh your axles, it's

gonna weigh your differential. If you got a solid rear axle it's gonna

weigh the whole thing with the brakes, the tires, wheels, so that's all pretty

heavy stuff. So if you have a rear-end weight of 1500 pounds, you know, generally,

I usually think about 300 pounds as an average weight for a rear-end. So I

would subtract 300 pounds off of that and then start doing my calculations for

how much weight it's gonna take to compress the spring. If you have any

questions make sure you give us a call on our tech line or send us an email.

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