Spring rate help?

synolimit · 08-13-2014, 09:43 PM

Quote:

Originally Posted by Rusty

Great sound effects!

Did you hear me fart from pushing on the car!

GSS138 · 08-13-2014, 11:18 PM

Quote:

Originally Posted by 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.

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.

j-rho · 08-13-2014, 11:56 PM

Quote:

Originally Posted by wstar

Ok so after all the other diversions, I still have a couple fundamentally-simple questions (one of which I already asked!):

1) Will I need to use shorter springs if I switch to a significantly stiffer spring and want to keep ride height and stroke about where it is today? Or should I basically plan on ordering the exact springs I have today, just in a different rate value? What would a normal person that knew what they were doing tend to do?

If you go with a stiffer spring of the same free length, you'll need to lower your lower spring perch (assuming you have that adjustability) to maintain the same ride height. If you would end up having to move the perch by more than 1", then it may make sense to get a 1" shorter spring, and move the perch less. As spring length gets shorter, you'll just need to remember to check to make sure you don't encounter a coil bind condition.

Quote:

2) The rear sway: it's a given I at least need to cut back to the stock bar. What about just dumping the bar altogether? I know others have dumped the rear bar and been happy in 350Z's, but I suspect this was in combination with an upgrade to stiffer springs all around. What's the worst that could possibly go wrong* if I dump the rear bar and fail to do (insert some other unknown thing that needs to be done at the same time)? Would the car get unstable in some way that I'd really hate?[/I]

Removing the rear bar will soften the rear relative to the front, which will shift the balance towards understeer - just like stiffer front springs would.
The only thing I'd suggest to watch out for -which probably won't be an issue if you have decent rate rear springs - is to make sure the new softness in the rear suspension, doesn't mean that it is compressing so much further, that it's now hitting the bump stops or something.

j-rho · 08-14-2014, 12:14 AM

Quote:

Originally Posted by 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.

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.

wstar · 08-14-2014, 02:39 AM

Quote:

Originally Posted by j-rho

Removing the rear bar will soften the rear relative to the front, which will shift the balance towards understeer - just like stiffer front springs would.
The only thing I'd suggest to watch out for -which probably won't be an issue if you have decent rate rear springs - is to make sure the new softness in the rear suspension, doesn't mean that it is compressing so much further, that it's now hitting the bump stops or something.

Yeah... so just thinking of the rear bar as extra spring rate, I started looking that. I don't know the rear motion ratios yet (for the shock or the bar), but nevermind that factor for the moment, it's probably somewhere around 0.8 or something, -ish.

So, the Hotchkis rear bar has a mfg-spec bar spring rate of 930 lbs/in at it's weakest setting (where I've had it for a while). Assuming the bar's motion ratio at 0.8 that would be ~600 (rate times motion ratio squared), and then I assume I divide that in half for the contribution to spring rate in each rear corner. So this means that the bar is contributing 300 lbs/in to my overall spring rate in each rear corner.

Let's ignore that I wanted to up my spring rates in general, and just focus on the idea of removing the bar and leaving the total spring rate alone, in theory...

So... if I just wanted to pull the bar to get rid of its side-to-side affects and leave my overall spring-rate as is, I'd have to bump my rear springs from ~500 to ~800, is what this sounds like to me. That sounds like a bigger jump than I would have expected, as it puts the rear springs significantly stiffer than the current front springs (which are 650 springs, and then if you toss in the 1970 lb/in front sway contribution it's effectively ~1280). It seems a little odd that just to remove the rear bar and cancel out that effect on rate, I'd be moving my rear springs from 150 less than the fronts to 150 more than the fronts - I didn't think it was worth that much.

Is this a sane line of thinking? Do those numbers make basic sense, aside from the totally fake 0.8 bar motion ratio? (I can fix the math for that later after I measure and get real numbers, but still, the general idea isn't going to change a lot). Or am I thinking about this wrong?

EDIT: in converting bar rate to "virtual spring rate", I think I left out also converting back through the motion ratio of the shock absorber which would change things further. But I think, if anything, that would make the +300 lbs/in value slightly larger anyways, so it doesn't really change the overall point.

j-rho · 08-14-2014, 03:07 AM

Couple thoughts:
The swaybar only behaves like a spring in roll, but not in dive/squat. If you take off the bar and up the spring enough to achieve the same roll stiffness, the car will squat less under acceleration.

If you're somewhat ok with balance but want to try removing the rear bar, upping rear spring rate in conjunction makes sense. The exact amount to do so you won't really know without testing. There are a lot of things like bushings and a chassis that flex, to make actual swaybar effectiveness less than theoretical - not to mention a small mis-measurement in bar motion ratio, can have a large effect on its apparent contribution. The suggestion of someone above, to get lots of spring pairs, is a good one. Some racer groups even have spring pools people trade in and out of, to make stuff like this cheaper/easier. If you think 300 is too big a jump, try doing half that - a 30% increase (500->650) in spring rate should be readily noticeable but not shocking.

The side-to-side thing of bars is generally misunderstood. If you remove the rear bar and substitute a stiffer rear spring that achieves the exact same roll stiffness, the load on the inside rear wheel at a given lateral g, would be the same as it was before with the bar. People thing the bar is "holding up" the inside rear wheel, instead of thinking about it as a natural effect of lateral load transfer.

FWIW, the fast guys I know of with these cars, are running rates in the upper half of what Shamu provided - around 1200 front, 850 rear.

03threefiftyz · 08-14-2014, 05:45 AM

Quote:

Originally Posted by j-rho

Couple thoughts:
The swaybar only behaves like a spring in roll, but not in dive/squat. If you take off the bar and up the spring enough to achieve the same roll stiffness, the car will squat less under acceleration.

If you're somewhat ok with balance but want to try removing the rear bar, upping rear spring rate in conjunction makes sense. The exact amount to do so you won't really know without testing. There are a lot of things like bushings and a chassis that flex, to make actual swaybar effectiveness less than theoretical - not to mention a small mis-measurement in bar motion ratio, can have a large effect on its apparent contribution. The suggestion of someone above, to get lots of spring pairs, is a good one. Some racer groups even have spring pools people trade in and out of, to make stuff like this cheaper/easier. If you think 300 is too big a jump, try doing half that - a 30% increase (500->650) in spring rate should be readily noticeable but not shocking.

The side-to-side thing of bars is generally misunderstood. If you remove the rear bar and substitute a stiffer rear spring that achieves the exact same roll stiffness, the load on the inside rear wheel at a given lateral g, would be the same as it was before with the bar. People thing the bar is "holding up" the inside rear wheel, instead of thinking about it as a natural effect of lateral load transfer.

FWIW, the fast guys I know of with these cars, are running rates in the upper half of what Shamu provided - around 1200 front, 850 rear.

More than 850 out back with no/small bar and hoos....

03threefiftyz · 08-14-2014, 05:48 AM

j-rho, GSS is a lost cause. I've tried before.

Rangerz · 08-14-2014, 08:31 AM

Appreciate all the information in this thread guys...keep the discussion going please

bkleeman · 08-14-2014, 02:10 PM

Quote:

Originally Posted by Super Werty

Who made the sway bar? I wonder if they would sell some.

What end links do you use with this front bar?

Do you guys run a rear sway?

The front sway was made by Tim Bell Racing and it's what they run on their Conti cars (GS #21 and #28). I'm sure he'd sell you some - It requires some hardware to properly attach and I think that includes the end-links.

We run a blade-style sway bar on the rear that was fabbed by Doran Racing. Its pretty soft - rates in the 300 lb/in if I recall correctly.

Shamu · 08-14-2014, 03:35 PM

This is "loose"

Chris Forsberg Formula Drift Atlanta 2014 - GoPro POV - YouTube

thompsontechs · 08-14-2014, 08:28 PM

I just typed a book and then erased it... here's what my gut or arse tell me... Make one change at a time drive it and then make another not forgetting the first. Everyone drives differently, I like a loose car and drive it well. If you are new, I would say you should go tight, but to think this or that is right for another driver is flawed. Don't get me wrong, if you are lost then any help is good and what some have said here can help you get where you want to go. I have driven for a living and the best car I ever had, my co claimed undrivable.

Find some numbers here and then learn what you like need to for yourself. No two cars are alike and no two drivers either.... end of line................

wstar · 08-14-2014, 09:14 PM

Yeah that's all the general idea. I prefer a slightly loose car. Step one should be downsizing or getting rid of the rear sway, but I'm also way overdue to up my spring rates as well - and while the swaybar is the bigger issue right now, dropping rate from that is going to make at least my rear springs suddenly a bigger issue, too.

So I'm probably going to end up making both changes at once. It'll be fine if it's somewhere in the ballpark of correct. So I'll do a bunch of math and season it with some random guesswork and then throw on a set of springs and see what happens

Really, the worst adaptation I've had to deal with so far was a simultaneous switch from high-treadwear tires to RS3's while also stepping down from a staggered to a square tire setup. Felt awful to me the first drive, but after a full weekend I adapted and decided I liked it better. I'm sure this sway+spring change will feel a little weird to me at first, too, but it'll probably be fine as long as I don't screw it up too badly.

synolimit · 08-14-2014, 10:04 PM

Quote:

Originally Posted by wstar

Yeah that's all the general idea. I prefer a slightly loose car. Step one should be downsizing or getting rid of the rear sway, but I'm also way overdue to up my spring rates as well - and while the swaybar is the bigger issue right now, dropping rate from that is going to make at least my rear springs suddenly a bigger issue, too.

So I'm probably going to end up making both changes at once. It'll be fine if it's somewhere in the ballpark of correct. So I'll do a bunch of math and season it with some random guesswork and then throw on a set of springs and see what happens

Really, the worst adaptation I've had to deal with so far was a simultaneous switch from high-treadwear tires to RS3's while also stepping down from a staggered to a square tire setup. Felt awful to me the first drive, but after a full weekend I adapted and decided I liked it better. I'm sure this sway+spring change will feel a little weird to me at first, too, but it'll probably be fine as long as I don't screw it up too badly.

Speaking of treadwear, do you check tire temps? I drove around the block after coil install and when checking rubbing and such when I got back I noticed the inner wall was hot as hell yet the outer was very cold. Obviously severe camber and getting it aligned tomorrow but it still made me think about temps on the track and wear. I'd assume even temps across the carcass is ideal? Thinking of buying a temp gun.

wstar · 08-14-2014, 10:24 PM

Yeah I use an IR temp gun to check things out sometimes. A proper pyrometer would be way better, but 9 times out of 10 the IR temp tells me what I need to know (and hell 8 times out of 10 I already know what the temp gun is going to say just by looking carefully at the rubber).

08-14-2014, 08:31 AM	#69 (permalink)
Rangerz Enthusiast Member Join Date: Jun 2013 Location: Northern Utah Age: 59 Posts: 476 Drives: 2012 370 Nismo Rep Power: 12	Appreciate all the information in this thread guys...keep the discussion going please __________________ Stillen Gen III/ NST/ Fast Intentions Non-Res HFC & 12" Resonated CF TDX/ Setreb series 9 OC/ SPL upper control arms/ Whiteline front & rear swaybars/ Uprev tuned by Seb@specialtyZ/ 319HP 262TQ/ Z1 PS Cooler/ Z1 SS Premium break lines/ CJM Road Race pump/Carbotech F:XP10 R:XP8 Nismo OC DIY

08-14-2014, 03:35 PM	#71 (permalink)
Shamu A True Z Fanatic Join Date: Jan 2011 Location: Nor Cal Posts: 1,059 Drives: 370Z Racecar Rep Power: 19	This is "loose" Chris Forsberg Formula Drift Atlanta 2014 - GoPro POV - YouTube __________________ Grant

08-14-2014, 09:14 PM	#73 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3594	Yeah that's all the general idea. I prefer a slightly loose car. Step one should be downsizing or getting rid of the rear sway, but I'm also way overdue to up my spring rates as well - and while the swaybar is the bigger issue right now, dropping rate from that is going to make at least my rear springs suddenly a bigger issue, too. So I'm probably going to end up making both changes at once. It'll be fine if it's somewhere in the ballpark of correct. So I'll do a bunch of math and season it with some random guesswork and then throw on a set of springs and see what happens Really, the worst adaptation I've had to deal with so far was a simultaneous switch from high-treadwear tires to RS3's while also stepping down from a staggered to a square tire setup. Felt awful to me the first drive, but after a full weekend I adapted and decided I liked it better. I'm sure this sway+spring change will feel a little weird to me at first, too, but it'll probably be fine as long as I don't screw it up too badly. __________________ 7AT Track Car! Journal thread / Car setup details

08-14-2014, 10:24 PM	#75 (permalink)
wstar A True Z Fanatic Join Date: Mar 2009 Location: Houston, TX Posts: 4,024 Drives: too slow Rep Power: 3594	Yeah I use an IR temp gun to check things out sometimes. A proper pyrometer would be way better, but 9 times out of 10 the IR temp tells me what I need to know (and hell 8 times out of 10 I already know what the temp gun is going to say just by looking carefully at the rubber). synolimit likes this. __________________ 7AT Track Car! Journal thread / Car setup details

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08-14-2014, 03:07 AM	#66 (permalink)
j-rho Base Member Join Date: Jul 2014 Location: San Diego Posts: 154 Drives: 1967 Camaro Z28 Rep Power: 11	Couple thoughts: The swaybar only behaves like a spring in roll, but not in dive/squat. If you take off the bar and up the spring enough to achieve the same roll stiffness, the car will squat less under acceleration. If you're somewhat ok with balance but want to try removing the rear bar, upping rear spring rate in conjunction makes sense. The exact amount to do so you won't really know without testing. There are a lot of things like bushings and a chassis that flex, to make actual swaybar effectiveness less than theoretical - not to mention a small mis-measurement in bar motion ratio, can have a large effect on its apparent contribution. The suggestion of someone above, to get lots of spring pairs, is a good one. Some racer groups even have spring pools people trade in and out of, to make stuff like this cheaper/easier. If you think 300 is too big a jump, try doing half that - a 30% increase (500->650) in spring rate should be readily noticeable but not shocking. The side-to-side thing of bars is generally misunderstood. If you remove the rear bar and substitute a stiffer rear spring that achieves the exact same roll stiffness, the load on the inside rear wheel at a given lateral g, would be the same as it was before with the bar. People thing the bar is "holding up" the inside rear wheel, instead of thinking about it as a natural effect of lateral load transfer. FWIW, the fast guys I know of with these cars, are running rates in the upper half of what Shamu provided - around 1200 front, 850 rear.

08-14-2014, 05:48 AM	#68 (permalink)
03threefiftyz Track Member Join Date: Apr 2010 Location: MD Posts: 536 Drives: 03 350z 6mt Rep Power: 16	j-rho, GSS is a lost cause. I've tried before.

08-14-2014, 08:28 PM	#72 (permalink)
thompsontechs Base Member Join Date: Apr 2014 Location: Rockford Posts: 129 Drives: 370 Sport Rep Power: 11	I just typed a book and then erased it... here's what my gut or arse tell me... Make one change at a time drive it and then make another not forgetting the first. Everyone drives differently, I like a loose car and drive it well. If you are new, I would say you should go tight, but to think this or that is right for another driver is flawed. Don't get me wrong, if you are lost then any help is good and what some have said here can help you get where you want to go. I have driven for a living and the best car I ever had, my co claimed undrivable. Find some numbers here and then learn what you like need to for yourself. No two cars are alike and no two drivers either.... end of line................