Spring rate help?
 

So, this is an image a guy shot of my car during the R4C event that's interesting. Look at the inner rear tire here: this is shortly after turning in to the left. I'm mostly likely already on maintenance throttle here given it's T16 (Sugar):

http://www.the370z.com/members/wstar...sr-houston.jpg

My tire wear has been pretty even at all four corners on the RS3's, but the above is on slicks. With the slicks, the rears are wearing more on the inside and leaving an edge of less-wear at the outside (as if too much negative camber). This pic seems to explain why.

The outer wheel lays down flat, but the inner wheel is nowhere close. (And yeah there's a little of that in the front, too, but it doesn't seem to be enough to dramatically affect tire wear in the net of a lap). I'm inclined to think the camber's fine if the outside tires are doing the right thing, and that getting the inside tire to behave is a matter of suspension...

I didn't make any suspension changes when switching tires, and even on the RS3's I know my springs are kinda weak. The easiest thing to experiment with (and what I should have thought to play with that day) is to stiffen up my damper settings and see if that helps, within reason (but I do need the dampers to move; I tend to run over inside kerbing intentionally a lot!).

I think the real change that's warranted here, though, is to switch to a much stiffer spring rate to help keep the tires pushed down flat. Does that make basic sense here, or should I make other changes first?

The current coilovers are JRZ RS1's (true type in the rear, single-adjustable), and the spring rates that came with them are:

Front: 650 lbs/in (~11.5 kgf/mm)
Rear: 500 lbs/in (~9 kgf/mm)

Like I said, they seemed a little soft for a full-time track car even on streetable tires. What would a good target guestimate set of springs rates be to try out to work better with race slicks (while hopefully not being totally undrivable on the occasion I run some streety tires on the car, or run race wets in the wet)?

Hmmmmmm

Your spring rates are stiffer in the back then front?
Also, what is your sway bar and alignment settings like?

I have 16kg front and 8 kg rear and it's pretty good on AD08R and Cup 2, thinking about 18kg and 10kg or more on slicks tho.

Oops. Yes, I think I copied them backwards. I flipped them around in the top post now.

I'm on Hotchkis sways on both ends, with the rear currently set at its softest setting (because that worked best for rear-end stability on the street tires - but then again I haven't re-evaluated that in a while, and my driving has improved and changed a lot since then. Perhaps the problem was more me than the car :) ). I've been hearing the ideal is to go to weak or non-existent rear sway and stiffer rear springs instead.

The other suspension components are stock other than SPL's front upper control arms for camber/caster adjust. Front is in the ballpark of -2.5 camber and 7 in whichever is the only reasonable direction on caster, I think. I set it at home with one of those cheap kits, and it's been a while, I should probably go re-measure and adjust sometime. I left the rear alone at stock-ish settings (with the changes from the car lowering ~3/4" or so), so I think it's gotta be around -2 camber there?

I should start writing these things down when I measure them heh, it's been months.

I am not Mr. Track but it seems to me that most people suggest stiff front sway soft rear sway. OR...is that just for autocross?

His Hotchkis is the most stiff front bar available, but the rear is a bit stiffer than stock tho.

Get the front as stiff as you can - you probably won't over do it. We're running between 1000 - 1200 lb/in front springs (900-1000 in the rear) with a custom swaybar made from .120 wall roll bar tube and the front still rolls over more than we'd like. See pic:

Hotchkis is the stiffest off-the-shelf bar that I know of tho, so you're left with just upping the spring rates.

Don't run the rear Hotchkis, way too stiff and most likely contributing to the inside rear tread lift. Go back to stock rear and see how it goes

Yeah, actually another local forum member here was going to sell me his stock rear bar, but I dropped the ball and forgot to follow up because right after that my engine blew up and everything else went on hold while I dealt with that :) Maybe I'll try that first and see how it goes next event (and up my dampers a bit too). And then work on upping the spring rates a little later and see how they pan out with different tires and in the wet, perhaps start at something like ~900 and ~800 lbs/in, or whatever values in that ballpark I can locate in matching springs.

Thanks for the input guys :)

Yeah going back to stock rear bar would be the first thing I try. Its cost effective and I know for sure a track Z shouldn't have that bar back there lol

I run 1000 lb fronts and 550 lb rears and thats not enough spring for slicks. You are way undersprung upfront. low front spring rate allowing rear to lift like that.

We are going to 1100 front and 700 rear maybe more! I drove on streets for couple years with 1000 lb springs and JRZ coilovers. Was downright comfy.

Really? I'm DDing my new 2 ways that just came in, 1000 fronts and 670 rears :tup: I'll figure out tomorrow I guess.

Would agree with all the above. The rates are low. In the pic, the front right is rolling over(as is probably the rear), and the rear sway is lifting the rear left.

Clint's suggestion is definitely the fastest, least expensive change though. Long term I would look at something more like 16kF/10KR if you otherwise like your current setup.

I was told by the company I bought my 2 ways from that the front and rear rates need to be closely matched for even balance. Like if you need a harder front you might also need to step up your rear. He advised to stay within a 5-6k range unless you're a drifter then it changes. Anyone else follow this rule?

I see Shamu is at 8k difference now but would like 7k and bkleeman is within that range.

Completely depends on corner weights and if you are trying to lean the car towards more understeer or more oversteer.

On my first set of coils(soon to be installed). I have opted for 10KF/12K rear. This will produce a front ride frequency of 2.0 and a rear of 2.3
2.0/2.3 = ~.86 which is on the understeer side, and is almost identical to the OEM ride frequencies. It's also almost the exact ride frequencies of the swift spec-R.

The mfgr's tune to this frequency on purpose, understeer is safe. Almost every single OEM vehicle is going to be close to this ride frequency. I figure I will stay close to OEM, but at a stiffer spring/wheel rate, as to not make too drastic of a change. The car will behave similar to it does now, but won't roll over as bad.

Now if you wanted to dial in some oversteer which is more typical of a race car setup(looser). You would bring the front rate much higher. Something like 14k/10K on oem spring location would produce

2.3/2.1 = 1.12. Which would be mild oversteer and is pretty well balanced and is probably what I will do next for a stepping stone.

The big no-no is to do something like 2.1/2.0 = ~1 as was explained to me by an engineer(this is not my math I just know the equations).

As he described it to me, anything in the range 0.9-1.1 is flirting with some real problems and can get you into trouble. You always want to aim outside of those numbers either towards understeer or towards oversteer.

Well, in my case I've switched to true-type rears, so I can't directly compare the ratios from the stock spring setup anyways. The rule of thumb for avoiding near-1.0 (I assume for harmonic reasons between front/rear bounce) makes sense, but I'll have to figure out how to do the freq calculations for my setup first.

My current setup is definitely oriented in the oversteer direction (not that I know the math, I just know that every single time I get close to being in trouble, it's from oversteer not understeer, even in a faster sweeping corner :p), and I'm pretty comfy with that.

I think you need to go back to that engineer and have him run you through it again...you didn't grasp it the first time.

2.0f/2.3r is going to be loose, 2.3f/2.1 is pretty nuetral and 2.1/2.0 is a little soft and probably still on the nuetrul side (tending towards oversteer)....

Fwiw, my race car sits in the 2.4f/2.25 and tends towards slightly loose on corner exit and that is with no rear bar.

Which one of you true type rear coils guys needs SPL toe arms?!?!?!

Agreed im running stock nismo bar in the rear

have to find out first. all i know right now im 57/43 weight ratio so the rear is way happy!

finally someone talking about frequency! i have no idea what youre talking about but was trying to tell someone and couldnt say it right so he had no idea what i was talking about. if you could PM we wont thread jack, i have a ??

1000lbs springs are still softer then bump stops :D

before any spring rates get changed around, i think that rear Hotchkis needs to go and be tested with stock. then further tuning from there.

with both the weight balance of the 370 NOT being 50/50,. and the high amount of both front grip potential with sqaure tire setup, decently high levels of unsprung weight, and the wishbone suspension, i think the front really needs a good amount of rate. depending what rear rate you need depends on spring location (stock or true coilover), sway bar selection in back (large, stock, or none), power level, and LSD.


I run G37S coupe rear bar

Ok one more thing: I know the exact brand and type of coils on my RS1's: they're HyperCoils, and their model number system is pretty simple (they go by "free coil length", basically a coil count, the I.D., and the spring rate). So the ones I have now are 8A0500 rear (8 coil, 2.25 ID, 500 lbs/in), and 6A0650 front (6 coil, 2.25 ID, 650 lbs/in). You can see their catalog page here: http://www.hypercoils.com/skin/front...Catalog_12.jpg , but basically I can pick any reasonable rate and coil count I'd want.... do I need to change the length when I change the rate, or keep the same length as the ones I have and just change rates?

Make it easy on yourself, just get a pair of springs in 50lb increments from 600-1500lb....

Best answer!

Syno, you actually setup perfectly for doing doughnuts in the snow.

350 completely and respectfully disagree. Disagree since the freq calcs include corner weights, The guy I am talking to is Gordon Benson from Koni that engineered the 2812 long body. I know Koni these days isn't the "cool kids" choice of dampers, but math is math. If you want email him at Gordon.benson@itt.com. Guy is awesome and will even get into the calculus of it.

Every post market "spring kit" out there tunes to something around .80-.85
because they can sell that product and not kill someone. Or at least not be sued for creating an "unsafe ride rate" as per the DOT.

that being said, I don't drive your car that you know intimately. I see what you are saying, because you know your car's frame, your sway bars, your tires, what you like, etc. better than I do, and are a much more experienced driver. But as for a baseline tuning point, and to understand how a suspension works(regardless of the car) the Front ride Freq/ rear ride Freq, tells you how the car is setup. <1 induced understeer. > 1 induced oversteer. That's not my opinion that's just physics. Doesn't tell you how to drive it fast, doesn't make you push the throttle when you know you maybe shouldn't, it's just a reference point.

:drama:

:p 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?

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

What end links do you use with this front bar?

Do you guys run a rear sway?

You might want to publish what Gordon said directly, as in re-reading, I think you'll find you've reversed things.

Increasing spring rate at an axle (front or rear) with no other changes, shifts the lateral load transfer distribution (LLTD) towards that axle. LLTD tells you how much of the car's lateral weight transfer is borne by either the front or rear axles in roll. An axle pair of tires generates the most lateral grip, when inside and outside are most evenly loaded, due to the tire load sensitivity curve.
If at Setup A, the front and rear had equal LLTD, and from there you stiffened the front springs, you'd now have a greater front axle load differential at a given lateral g, than you had before. Greater load differential = less grip. Less grip at front means shift towards understeer.

The ratio of ride frequencies is one data point in the understeer/oversteer equation but hardly the only one. Sway bars, resulting geometry of the outside tires, static weight distribution, wheel/tire stagger are a few of the other variables.

Changing roll stiffness at one end can have second-order effects (like improved resulting geometry due to less overall roll) but the primary effect is to increase the load transfer of the stiffened end, resulting in a shift of grip to the other axle in cornering.

...but you don't have to take it from me - there are countless texts on the subject, encourage everyone to check them out and discover how it all works, for themselves.

You're 370z isn't 50/50? :hello: I can help you get closer.

whats your weights though? im on swifts till tomorrow and since they are 10k and 10.5k id think with the "math" that'd be more in the middle of under/over? but my rear is so damn loose because you can only gut the rear out, its the weight making me loose and not the rates id think. maybe you too?

fyi, i just drove to a scale and cut the wheel width in half and used that as my front to rear weight.

lol got mine from brian, thanks for the referral :tup:

dear lord, this reminds me of National Treasure, Riley says "'why cant they just say go to this place, here's the treasure, spend it wisely." the search for suspension just never ends. just clue after clue.

I give up.

:ugh:

I've gutted my car fairly thoroughly throughout at this point. I'm sure a little more was removed in the rear than the front, but it's not like my car is super-light in the rear. Having a full cage in the car restores a little balance, too. I haven't put it on scales or corner-balanced it yet, partly because I'm lazy and partly because I know I have more-significant setup changes than that left to make.

You'll notice there's a lot of things I just haven't measured or done yet for where I'm at, which may seem a little odd. The thing is, I'm a super-geeky guy, and I'd have a natural tendency to over-engineer all of this and math out on it and nitpick a thousand details. If I let that side of me run wild, I'd be making like 4 significant setup changes between every run on the track and trying to blame everything that happens on some subtle issue with the car even though it probably only makes 0.5% difference, and even then only to a much better driver than me.

So I tend to consciously try to push myself in the other direction. I just go drive, and if the car doesn't feel seriously out of whack, then it's up to me to drive the car and adapt. It's probably better for my skill development anyways, and it's nice that the car's response is relatively stable from run to run most of the time, even if not optimal. I try not to futz with any settings during a track-day/weekend unless I think something is really feeling unstable and strange, or if I think there might be a mechanical problem with the car. And I try not to over-engineer things between, either, or I'd waste so much time on tweaking and math that I'd lose my day job :p And honestly, I have no good judgement yet on exactly which items are worth the time spent obsessing over, and which are just nitpickery for -0:00.001 lap time in a hyper-competitive environment that has no bearing on me today.

But yeah, especially now that I seem to have finally broken out of another skill plateau and I'm feeling pretty confident in my driving, my suspension needs some geeking on in the near future, at least one little burst of it to consider these basic suspension issues and get the car up to the next approximate level of goodness. Even so, the primary thing driving me to start toying with suspension again isn't so much lap time as getting my tire wear even on the slicks so I don't destroy sets of tires too fast.

I have no idea what this even means, but I don't suspect wheel width ratios is much of a determinant of weight distribution.

Great, here's me on the track then at 3 minutes

https://m.youtube.com/watch?v=tj_cW7aoRdQ

I mean I drove to a scale for semi trucks. I measured the distance from the front tire to the rear tire. I split that distance in half, about where my torso sits in the drivers seat. I drove on and parked so the front half was on the scale. Then I drove the back half on with the front hanging off. That's how I got 57/43. I figure its as good as any to find the front to rear ratio. Till I get my cage and add 100lbs back to the back, no matter what I think I'll have over steer.

I need to go again if it truly works and also drive on with right side/left side/one tire at a time. Figure that way I'll know all 4 corner weights for free and give me an idea about ballast. I like math too and doing this stuff!

I Completely agree with this, but I am not counting grip, sway bars, or anything besides the motion ratios, corner weight, and spring rates. I am just talking about a natural frequency that the car exhibits when it goes over a bump. It's something that is there by the manufacturer on purpose in every car. And if you take those freq and divide them, I am completely speculating here, but I will say that 95% of the cars on the planet rolling of an assembly line are in the range of .80-.90.

If you calc the rates for every single post market spring kit or out of the box coil over solution, you will either get a number between .80 -.90 (Understeer)
or you will get something in the range of 1.13-1.25 (looser rear end).

(Assuming close to OEM un-sprung corner weights)

Swift Spec R= 2.0115/2.2145=.90

Tein S-tech= 1.682/1.87 =.89

Nismo T2 motorsports springs = 2.0821/2.4224 = .859


Now let's look at some popular performance coils

Tein Flex = 2.2035/1.9833= 1.11

Stance GR= 2.2035/1.9624 = 1.12

Megan Racing 2.0115/1.6650 = 1.21 (loose!)

Edit:

Synolimit's Setup 2.6880/2.0361 = 1.32 (have fun cowboy)

Our OEM(non nismo) 1.6334/1.8563 = .89


This isn't a coincidence!


Again, it doesn't make your car go fast, has nothing to do with grip, doesn't get you trophy girls. It's just a baseline calculation that you can use to have a reference point for what you can expect out of your spring, your motion ratios, and your corner weights to do. Of course putting the tires, driver, sways, fuel, etc on top of this number changes everything. But it's nice to have a solid starting point :).


This PDF explains it better than I can: Freq of Ride rrates

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.....

Hey I grew up in Toledo, I have done my fair share of doughnuts in the snow.