Spring rate help?

j-rho

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.

Shamu

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

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Grant

synolimit

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

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.

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13 370z-

03threefiftyz

I give up.

wstar

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 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.

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7AT Track Car!
Journal thread / Car setup details

synolimit

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

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

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13 370z-

synolimit

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!

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13 370z-

GSS138

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

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Current Mods: Vorpal Weapon +5.

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.....

GSS138

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

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Current Mods: Vorpal Weapon +5.

03threefiftyz

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

Shamu

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.

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Grant

GSS138

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.

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Current Mods: Vorpal Weapon +5.

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.

03threefiftyz

j-rho,

Mo CAM with this please....