Spring rate help?

GSS138 · 08-13-2014, 12:17 PM

Quote:

Originally Posted by 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.

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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