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

Youre right that math is math. Sometimes math cant account for weight dynamics of certain cars, tires, alignment settings, etc. Way too many variables. Practical expreince outweighs math everytime in my expereince on track. I have worked with top suspension guys around world on numerous cars and while motion ratios are good benchmark they arent good at factoring what is happening with swaybars dynamic loads etc. And I have see fast setups that completely defy what experts would calculate with standard frequency formulas.

What I have seen with some regularity for full coilovers on 370Z race cars is front range of 1000 to 1200 lbs and rear of 600 to 900 lbs. These are on cars races in series such as Continental and Pirelli and on either DOT or race slicks. Full on race slicks do need signficantly more spring due to stickage factor. I usually jump 200 lbs from rates I use for DOT tires minimum.

And differnt tracks may dictate changes as well. Im planning on having a range of springs from 1000 to 1200 front and 600 to 900 rear. I just know my old DOT setup of 1000 front and 500 rear is allowing too much rollover with slicks.

Absolutely 100%. And like I said, these numbers sure as hell don't teach you how to drive or win anything for you.

But what they are useful for is tuning.

So if you know your car is setup with say a 1.15 ratio, and man you just need the *** end to swing around a little bit faster, you can now with no guess work select a spring that is going to help move your car towards 1.20 which should make it a little looser.

It's just a tool and a reference. And it sure as heck can't tell you what you like or prefer, it's like saying "hey it's 70 degrees outside". Some people might like it, some people might not. Some people put on a jacket, some people go swimming.

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.

j-rho,

Mo CAM with this please....
https://farm4.staticflickr.com/3853/...2a4ca503_b.jpg

Lincoln is too far from SD when there's no jacket at stake.

Troof.

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.

I should have given up when I said "I give up"...

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.

https://m.youtube.com/watch?v=q5pESPQpXxE

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

Sorry OP


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

...And taking setup advice from DOT street tire AX guys on a track car is dangerous. :icon18:

I like this purple car.

:icon14:

Looks blue to me.

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? :)

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?

* - https://www.youtube.com/watch?v=20KJhBX9xtE

Have you spoke with Z1 on what spring rates they use on kleemans car? I would just start with a popular track inspired setup then refine it from there.

Well I've got a good idea on ballpark spring rates at this point (and a little confirmational math to do before I pull the trigger, which will be after I've dealt with the rear sway). Keeping in mind that I don't want to have to swap springs constantly at this stage for different tires and don't want to be too unstable on wets or r-comps, I'll probably shoot a little lower than the track specs listed in this thread, but still considerably higher than where I'm at now. Something in say the ballpark of 900 and 700 - which would be approx the same ratio of raw spring rates as what I have now, with both ends boosted by about 30%. I know there's more math to be done than that, but it's a starting point guestimate at this stage. I'm gonna go measure the suspension later today or tomorrow so I can make some easy conversion factors for F/R spring rate -> F/R frequency.

Great sound effects! :icon17:

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

good to see the Z track people putting enough 2 cents each to get a informative thread into page 4 :D

Did you hear me fart from pushing on the car! :icon18:

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. :wtf2:

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.
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.

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.

:twocents:

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.

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....:eekdance:

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

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

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.

This is "loose"

Chris Forsberg Formula Drift Atlanta 2014 - GoPro POV - YouTube

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................

:) 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.

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).

You want not more than 10-15 degrees C total spread between inner, middle and outer tyre measurements and the spread needs to be even. If the temps inner to middle are close, you can drop some camber.

The other thing to remember is that unless your pit is closest to pit entry, you will drop temps in the time take to transit the pitlane .. can be as much as 10 degC or more.

An R-Spec tyre that measures under 65-70 DegC is probably not working hard enough to generate maximum grip.

An infra-red temp gauge is an approximation only - you want a pyrometer with a probe to get into the tread proper for accurate readings, UNLESS the IR technology you are using is top-shelf (professional motorsport quality)

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.

Eh, I doubt there's a ton of difference in various IR temp gauges. They're just a simple scientific instrument, and they have a certain accuracy and work a certain way. My Fluke (that I originally bought for electronics stuff) claims 1%, and coming off a DE cooldown lap and all the way back into the paddock I'm sure contributes way more error than that. I get that the the pyro in the carcass in the hot pit is more-accurate, but at this level I generally don't need to be more accurate. I just want to know the general shape of the temps: which band of the tire is running hotter or colder.

This is kind of what I was talking about at one point earlier, about trying to find out what it really matters to obsess over at an amateur/learning level. There's a pretty wide gap between "what you need to measure/adjust/fix just to make the car reasonably-drivable and not destroy tires", and "what you want to do to squeeze every thousandth in tight competition". In some areas I still have no idea where to draw the line yet. But I'm pretty sure at this point that tire temps/pressures, as critical as they are to the car, can be done for DE-level stuff with just an IR temp gauge and a simple pressure gauge after getting back to your parking spot in the paddock and still get you in the ballpark well enough. Most of the time you can even see gross pressure/alignment errors visually if you just look at how the rubber melts/wears.

It is not so much about differences, but the fact that an IR temp reader reads the surface temp but what you really want to know is the temp in the underbelt

Anyway, for amateur purposes, you are mostly correct - it is the relative difference between inner, md and outer temps that is key ... you want an even graduation of temps - say 5 DegC apart - across the face of the tread as a lead indicator to camber sweet spot. What I am trying to communicate is that you want to measure these differences as close to hot-track exit as you can - i.e. by the time to trundle down the put lane and turn to the paddock out-back, your graduations will have morphed significantly enough to distort the knowledge you are after. Tyre pressure will be affected as well, but nowhere near the same extent.

For example, real-time monitoring of my RHF tread surface temps at T12 at Philip Island GP circuit (290mm wide Dunlop SS12 compound slick) now shows (inner to outer) going from 88/85/82 to 108/100/94 in the space of 150 metres as the car is turned in and accelerated thru the mid-corner. Once I take steering angle out of it, the temps drop 15 DegC in the next 300 metres. I borrowed the setup from a semi-Pro team because I was blistering the inside of the RH front at PI after a track resurface a few years ago because the settings I was using from prior seasons was too agressive and we had to take a bit of camber and some toe out of the car to get the tyre to last (blistering set in with temps over 115 DegC on the SS12).

One of our 370Z owners over here (Keith Flanagan - KF365 here) had a couple of delamination/tyre failures with Dunlop DZ03G in T12 as well, because it is a very hi-speed corner and the car stays loaded for an eternity (maybe 8-10 seconds from turn-in until you pull all the steering out of the car). It is the temps in the carcass that lead to failure, not the outer tread surface ....

On a cold day where track temps are ~15DegC, by the time I exit the track and get to the top of pitlane (where crew can use a probe on the tyre), the IR surface temps can be back to 60 DegC or less but the temp under the surface layer can be up to 15 Deg higher - so it can be very easy to get confused. That is my real message !!

Toe (and caster) can also influence heat build-up on turn-in and in the case of toe-out, inner temps in straight running.

This thread had an earlier post on the inter-connected-ness of springs, suspension settings and even driver habit and if I have learned one thing in the past 40-odd years, it is that there is always something new to learn, that simple things usually work best - because us amateurs don;t have the funds to invest in full-time engineers to can run the calcs all the time. There were a couple of book titles recommended as well which are a great source of information and the basis for personal experimentation.

Keep experimenting and you acquire knowledge .... and tread your own path !!

As long as this thread is wobbling all over the place off the original topic anyways ... :)

Here's another question for those more-knowledgeable: does balancing wheels/tires really matter on a racecar? I've googled on this a bit and seen conflicting advice. Some seem to think it matters, others take the line that it doesn't. Those that say it doesn't matter argue that (a) You'd mostly only feel the vibration coasting at a steady speed, which you almost never do anyways, and (b) aside from a potential few uncomfortable vibrations, it doesn't really damage anything or hurt performance anyways. It would save time on the (increasingly-frequent) tire re-mountings not to bother with it, and then I wouldn't have to worry about taping down wheel weights and/or worrying about them flying off or possibly getting stuck in the brake caliper somewhere, etc. That and let's face it, with all the tire worms inside the wheel and the pickups on the outside, and probably the tire slipping into a different rotational position on the rim regularly, how well is the thing really staying in balance throughout the day anyways?

So: to balance or not to balance? What do pro race teams do?