surfingsk8r

Ill do my best to keep this short.

I am building a new car (97 GSR) and am wanting to get away from drag racing a bit and start doing some HPDE's. As such I have been planning my suspension set up and I have become fixated on spring rates. I have pretty much set my mind on getting PIC Select R3's but I am actually thinking about swaping the springs so that the 14k springs are in the front and 12k in the rear. Ultimately the purpose of this car is multi-use. I want to be able to run a few 1/4 mile passes with it when I feel like it, or take it out on a sunday for a quick drive (hour max probably, not a DD) and I want to be well set up for road coarse purposes.

Here is my line of thinking, If I have done my math right regarding MR and wheel rates then with the 14k f and 12k r I will have a similar suspension frequency which should improve ride quality (i think), plus I am not super interested at having a car that has a tendency to oversteer and I figure I can tune that a bit with sway bars.

For reference, I have zero track experience in a car that was not a kart, but I have years of experience on motorcycles, both racing and track days, so I am familiar with basic principles, and I am a bit obsessed with setup as it has been very beneficial for me in that arena.

So, am I overthinking it? Should I just leave them alone? Is the Select R3 the wrong coilover for me?

Any and all help is appreciated. Thank you.

Greyout

I like the idea of stiffer springs up front and tuning with bar settings / removing bar

boxedfox

What sort of ride frequency numbers are you getting with those rates? I like to have the rear ride frequency slightly higher than the front so the car settles faster after going over big bumps and dips for ride comfort.

surfingsk8r

The math I did was as follows:

measured MR as .66 front and .74 rear

Then I used this formula to get wheel rate WR = MR^2 * SpringRate so FRONT WR = 341.5 = (.66)^2 * 784 <-- 14k spring, and REAR WR = 367.9 = (.74)^2 *672 <-- 12 spring

Then to get the suspension frequency I used this formula: SF = (187.8) * (sqrt(WR/spring weight)) so FRONT SF = 122.7 = (187.8) * (sqrt(341.5/800)) and REAR SF = 167.9 = (187.8) * (sqrt(367.9/460))

So, to put it more plainly here are the final numbers

14k Front 12k Rear

MR = .66 Front, .74 Rear
WR = 341.5 Front, 367.9 Rear
SF = 122.7 Front, 167.9 Rear

Whereas if I leave the springs as 12k front and 14k rear I get this:

MR = .66 Front, .74 Rear
WR = 292.7 Front, 429.3 Rear
SF = 113.59 Front, 175.2 Rear

As you can see the difference is quite large when the springs are in their "normal" orientation for the PIC Select R3's, which is why I was questioning switching them.

KoRn_vIRuZ

How did you come up with that formula for ride frequency and what units is it using?
It needs to take weight into account. Since the car is heavier in the front, for similar spring rates the ride frequency will be much higher in the rear.

14k front/ 12k rear is not a choice that is optimized for comfort at all. It is just trying to make the car rotate, at the expense of comfort.
If you want ride comfort you need softer springs in rear.

Here's an Excel file I wrote, hope it helps:

surfingsk8r

The formulas used are from Eibach. Here is the url to that info. https://eibach.com/us/p-101-suspension-worksheet.html

Also I agree with you that the rear would be too stiff, which is why I want to swap the front and rear springs. They come from PIC as 12k front 14k rear. By swapping them to 14k front and 12k rear I "should" be making that problem a little better on paper, but that is why I am asking the folks who are in the know for racetrack use. I am not looking for a comfortable ride exactly, but I dont see the sense in running it as 12k front and 14k rear as it comes, which again is why I am asking the question.

killerpenguin21

on my HC integra i run 1000lb front and 700lb rear with no front bar and the big asr bar, so thats like 18k F/13k R, and it handles very,very well.

flipping those springs like you said is a good start imho.

surfingsk8r

So I found some pretty good information about suspension frequency that I though I would share the link to here.

http://downloads.optimumg.com/Techni...Tech_Tip_1.pdf

That article basically talks about pairing suspension frequencies for different purposes and then goes into spring rate choice from there. As it stands I think I will be at a pretty good starting point for me to flip the springs to be 14k front and 12k rear, but if I can swing it through PIC directly or a vendor I will probably shoot for 14k front and 10k rear as I think that will be optimal for my purposes at least for now.

Thank you all for the input, i learned alot from the points discussed and the subsequent research.

PS. that article above is one of several to see them all go here: Technical Papers - OptimumG