Spring rate help?

wstar

I'm sure I'll end up closer to that than I want to be, eventually. But the nature of my earlier question, if it wasn't clear, is more like: if I change a spring rate dramatically and want to maintain approximately the same suspension stroke and ride height, do I need to buy shorter springs when I buy stronger springs, because they won't be as compressed when the car is static?

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7AT Track Car!
Journal thread / Car setup details

clintfocus

03threefiftyz

I give up.

03threefiftyz

I think you need to heed Jason and I, take a few minutes and review how f/r frequency plays into the handling of the car.....

03threefiftyz

Oh...keep in mind syno is not running a spring in the bucket.

synolimit

Correct. True type as of today. Well maybe not wtf??!!!

Sorry OP


https://m.youtube.com/watch?feature=...&v=l5i_kyW7_Y4

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13 370z-

Shamu

...And taking setup advice from DOT street tire AX guys on a track car is dangerous.

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Grant

Rusty

Great sound effects!

Trying to learn from this thread, and my mind is going hu.............................

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"The Difficult Anytime, The Impossible By Appointment Only"
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synolimit

Did you hear me fart from pushing on the car!

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13 370z-

j-rho

Sure every car is different, but increasing front spring rate with no other changes (increasing the ratio you mention) will make the front tires do relatively more work in a corner, which as a primary effect, shifts balance towards understeer. Your generalization is backwards of the general truth. If you want to make a case the general truth does not apply for some reason to the Z, you need to be able to explain why. You also need to be able to separate a discussion around bump handling (where shocks come heavily into play) vs. handling balance at steady-state limit cornering.

I encourage you (and anyone following along while scratching their head) to get a basic education in vehicle handling dynamics - Herb Adams, Fred Puhn, Paul Van Valkenburgh all have fairly accessible texts on the subject. A few $ for a book and a few evenings of reading, and you'll be much better equipped not only to understand what's happening with your own car, but to help others in their pursuits.

GSS138

fair enough and I agree with you, but feel my point is being missed a bit, as I am not addressing over all vehicle handling dynamics, weight transfer, tires, or anything else. All I am saying is this:

There is a ratio between front and rear ride frq that will tell you if the car has a tendency to oversteer or understeer.

If you want to change that tendency-change that ratio.

To redo my example, let's go back to our OEM rates:
I am using 392 front springs, and 440 Springs (listed OEM rates I could find)
They produce a ratio of:
1.6334/1.8563 = .89

Do you not find it interesting, that using completely different spring rates, this same .89 number is produced by just about every post market spring kit within a few decimal points?

Swift Spec-R's claim 10K and 10.5K so approximately 560F 600R
they produce a ride frequency on the same car of:
2.0115/2.2427 = .89

Much stiffer springs, totally change the way the car handles, so why is that .89 ratio still popping up?

All I am saying is that .89 is not a coincidence and was put there by your car manufacturer, and by Swift, and Eibach, and by every other lowering spring I can find rates on.

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j-rho

By itself, it can't begin to tell you that.

What you might be able to say - if you had a neutral car, and then you increased front spring rate, or softened the rear spring rate (increased that ratio value), the car would probably tend to understeer. But that's the opposite of what you're saying.

GSS138

I am dividing front/back, you could just as easily divide rear/back and see it inverse. All that matters is the number of units it is away from 1.

Just like 90 is 90% of 100, and 100 is basically 110% of 90(with some rounding problems). Pretty sure we are on same page.

What I am getting at is that if you mess with that ratio, it induces one or the other-oversteer or understeer. If you think the car understeers, you can reduce that understeer by 10%, or you can increase oversteer by 10% the same way-by increasing or decreasing that ratio. The factory sets it a particular way to make the car safe(.80-.89 generally, or 1.1-1.9 inversely). Almost across the board unless you buy a Ferrari, factory race car, or something else I can not afford.

The post market spring kits aren't reducing understeer or increasing oversteer with their rates(none that I can find and will post all the ones I know if you want). They are just increasing the ride rate(not to be confused with ride frequency). Increasing ride rate is great, and yes will reduce some understeer naturally on a car where the suspension is too soft overall. That is not what I am talking about at all.

An experienced track driver of a car instinctively knows, that a ratio of .89 (as I describe it) is not "fast". That's why the "performance coilover" solutions invert that number and come in at ~1.11(or .89 of OEM understeer the way you are describing). It feels fast! And by all accounts is fast. It's a major improvement over the understeer induced slosh bucket designed by the oem setup engineers.

The higher wheel rates alone make the driver feel faster, take the slosh out of the ride, and they also help prevent suspension geometry problems by eating up some shock travel and lowering CG. It's honestly a brilliant solution at a very good price.

So at that point , unless someone has a question, I give up too.

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j-rho

Not trying to argue about it man, I sincerely hope this discussion in some way helps somebody learn a little more of the basics of things.

You're hung up on this ratio that is just one small part of the picture, and your understanding of it is backwards. If you want, try putting 2000lb. springs in the rear of your car, and 500lb. in the front - the ratio will be way less than .89, which according to your equation, would make the car understeer like crazy. Go try it (not on the street! somewhere safe!) and report back how the car handles - bet you'll find it oversteers like crazy.

The ratio is but one variable. Adding front camber arms to an otherwise stock Z will give the front more grip, which will make it more oversteer-y - but the ratio would still be .89. Putting wider and stickier wheels/tires up front only would increase front grip and make it more oversteer-y, without changing the ratio. Putting on front aero devices to give the front more grip at speed would make it more oversteer-y, without changing the ratio. And on and on... As soon as you start making any changes to a car, including lowering, a lot of the assumptions that went into the factory handling balance go out the window, and the ratio of front to rear ride frequencies really becomes meaningless. What matters is that the car fits the needs of the owner/driver for what they want - whether it's lowest laptimes, good performance while retaining street manners, or whatever.

On some car, in some conditions - possibly even a 370z, a f:r ride frequency of .89 might just be perfect - but that value is arrived at as a result of having optimized all the aspects of the chassis/suspension and its setup that matter - not because anyone was trying to hit (or avoid) that value.

03threefiftyz

j-rho,

Mo CAM with this please....