Spring rate help?

GSS138

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.

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03threefiftyz

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.

GSS138

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.

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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.

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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synolimit

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

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13 370z-

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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synolimit

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 ??

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13 370z-

clintfocus

1000lbs springs are still softer then bump stops

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

GSS138

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

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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-

GSS138

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

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