Spring rate help?

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.

__________________
Current Mods: Vorpal Weapon +5.

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.

GSS138

Feedback much appreciated. And that's why I am here, to discuss it . Appreciate the opinion and congeniality.

You actually raised a really good point by suggesting putting 5000 lb springs on the rear. Yes, the damn rear would skate worse than Tonya Harding at that point lol.

With a 5000 spring in the rear and a 600 lb spring in the front, the ratio would be .33. This makes me wrong. Everyone knows that a 5000 lb spring in the rear is going to make the rear un-dampable unless the rear weighs 2500 lbs per corner. That's what you are missing. The spring rate doesn't matter, it's the spring rate and the corner weight.

But that got me thinking as well. If this is an inverse function which I know it is, then it is exponential as well. Let's do the opposite of what you are suggesting and put a 100 lb spring in the front of the car with a 600 lb spring in the rear. Guess what, car understeers like whoah.

What's the ratio? .39. Wow, that's really weird, .33 is close to .39. So why does your 5000 spring in the rear make it oversteer, and my 100 lb spring in the front make it understeer?

Everyone knows that putting a 100 lb spring underneath a 750 lb corner is going to be near useless. Just like anyone that puts a 5000 lb spring under a 750 lb corner is not going to get good results.

Assuming a motion ratio of .62 at all four corners(close to oem) if the car was perfectly corner balanced at 750 lbs each, .62 * 760 = 465 lb spring. Lets put 465 lb springs on a perfectly balanced car, by my math, it would produce a ratio of 1. Let's for argument sake assume that is a very bad idea.

So, you can either stiffen the front or soften the rear. lets add 100 lbs of spring to the front. New ratio = 1.06

This will probably not have much effect, tell me if you disagree.

Lets add 100 more. New ratio = 1.15. Wow, big change(exponential actually).

My guess is that this will drastically reduce understeer Since the front will not roll over and the fronts will transfer weight to the back much easier. Tell me if you disagree.

Lets add 500 more lbs of spring. ratio 1.52.

My guess is the front of the car at this point is barely controllable and is skating all over the place , not quite as bad as Tonya at the Olympics , but is definitely prone to break loose. A 750 lb corner sitting on top of an 1150+ lb spring barely allows the dampers to do their job.


so we went from the following ratios

1.00 Not a good idea.
1.06 Not much better.
1.15 If we agree, we reduced understeer( or added oversteer)
1.52 Turned the front end into a Frisbee.

the same works in reverse

1.00 not good idea
.94 not much better
.85 Increased understeer (or removed oversteer)
.48 turned the car into a knee board with no rudder.

__________________
Current Mods: Vorpal Weapon +5.

Megan370z

On slick I wouldn't run anything lower than 900 *16kg* in the front !!
Now with the aero its an ever bigger number !

as far as running an 1150+spring , Its not un-commun to see a car which can be Pro or Amateur driver with nearly as much spring rate and they wouldn't go much below than this with slicks.

and remember that 1150 spring on a 750 corner, Im pretty sure the car is moving and seeing over 1g in the corner.. isnt that bring that corner to over 1500 llbs ? then you have 1inch and half of travel due to weight transfer.. which is relatively acceptable in my book for 1g corner.

math paper talking is quite different when you are actually driving the car, it will bring you close but the rest its all feeling and how the car react.





I haven't gave my opinion on the first picture Wstar posted,
For his setup I would recommend 16kg *900* front // 12kg *672* rear with the stiffer front bar and then the stock rear.

this is my new baseline w/ aero I will be using when I'm fit enough to get back on the track. I know the front wont be enough but its a baseline.

__________________
Megan Journal *Click Me* ....................One Man Team Motorsport *Click Me*

Shamu

For you guys who like "loose" cars what does that mean?

I like a balanced car that transitions well and is getting maximum mechnical grip from the tires. Not too much understeer and not much oversteer so I can managing turning with brakes and power application. I havent found too many road courses or hillclimbs where excessive oversteer is benificial .

So isnt what somone who is going to track wants is nuteral handling car with excellent transistory response for given tire selected? All this focus on loose or not loose seems to be foreign to me. Focusing on what spring and bar combo can slightly increase or decrease understeer and oversteer to your liking is probably better focus. Loose car as I know it isnt fast. But then I have been in very well buttoned down race cars with huge spring rates that arent "loose"

__________________
Grant