Need help with Spring Rates and set up on my NA Fat Cat suspension
 

I have a Fat Cat suspension with FCM Elite coilover package and 600/450 spring rates on my NA. I am using 225/45/15 NT01's and my rear end is too loose on track. My Racing Beat 1 ⅛ tubular sway bar in front is set to full stiff with rear sway bar completely removed. Does anybody have suggestions as to what is wrong with my setup and suggestions for getting it right for driving on the track? I am an advanced intermediate driver.

Needs more front roll stiffness/spring.

go to 700/400. Or in your case, i guess 800/450.

Thanks for responding. Does bump stop density have anything to do with the final spring rate ie if I change the stops would you expect an improvement ?

only if your springs are too soft for your ride height/grip level.

That doesnt sound right... define too loose ? When and how does it happen ? The oversteer without a rear ARB is really strange. What alignment ?

I've got Yellows with 600-400, FM swaybars and with the rear too low (leveled rake w/ driver) I needed to put the rear ARB to mid setting... front was full stiff. Still not too oversteery, just a complete lack of traction whilst cornering cause open diff lol, rear had no travel.

What is your pinch weld ride height and what are your alignment settings?

What weight, ride height, alignment, condition of tires,condition of track, and weather? And at what point does the over-steer happen and what type of turn? Entry, mid-corner, exit? Constant throttle, increase throttle, decrease brakes and where is the steering angle at with all of those when it happens?

Have you talked to Shaikh?

"loose rear" means too much oversteer coming on so quickly that it can be difficult to correct for in time either with throttle or counter steer and therefor more spins or wheels off track than Id like
Alignment is neg 3.3 and 0 toe in front and neg 2.8 with 3/32 toe in rear. Its definitely improved since I increased front sway and removed rear- and of course there is my driving to add into mix- however Ive had more advanced drivers try it and comment that they really enjoyed driving but felt it was too loose in turns- they enjoyed drifting through corners-me not so much. Also this is a Kswap car so I have a lot more power than standard

Im looking at about 12.25" front and 12.5 rear height- so slight rake forward. car is around 2400 with me in it. I d say it happens leading to mid corner when brakes are completely released. I had a consult with Shaikh and he was very helpful- hes on with the sway bar changes and I just now received something from him Im excited to try called spring rubbers. Havent seen these before but looks like inserted into coil adds to resistance. Will check into these today and let you all know

The setup really doesn't make sense. The FRC is >74% from rough calculations. That would be the setup with the FSB on the softest setting, and I don't feel like measuring the different in the arm length at full stiff. That is much higher than a stock NB, so it should be biased toward understeer in a steady state corner. The front spring rate is also rather low for R-compounds, (which may be causing interaction with the bump stops) but again, that would induce understeer. You should read up on 949's website for a rough setup guide. I would start with increaseing front spring rate and see where that gets you; it's obviously too low. I would throw that flat ride tuned setup out the window on a race car and setup the car for maximum grip.

No offense to Shaikh, but he focuses an awful lot on the math and numbers of suspension design and not nearly enough on how the cars actually function in the real world. You are not the first customer of his to complain about loose handling in your 600/450-equipped car, and you won't be the last. There is no amount of setup bandaiding, bumpstop tweaks, valving, "spring rubbers", or anything else that will fix your car's balance. You need stiffer front springs (700/750/800) or softer rear springs (325/350). You can fix it now or waste a bunch of time on other solutions and fix it later, the choice is yours.

I really dont want to waste a bunch of time trying stuff that wont work when there is a straightforward solution available. When Ive asked a little at the track I realized that most "fast guys" are running 750-800 at the front. So thats what i figured to do. The problem has became more obvious with my higher speeds after the kswap was done early this year. Im not as knowledgable as many of you and when I contacted Fat Cat he was pretty adament about not changing the spring rates so I started looking at other options and here I am! I actually dont know how to order springs of the correct size ( or even what the size is) so appreciate all your help

They're OTS bilstein shocks with a sleeve over it, so it will be a standard 2.5" ID spring. Measure the length of your current spring and buy an 2.5" ID 800lb spring in that length (chances are it's a 7" or 6" long spring).

Hyperco or Eibach are good value and top quality.

+1

Thank you!!

OK one more thing- If I leave the rear at 450 am I better with 750 or 800? Is it significant? Thanks

I would do 750# fronts, add extended lower balljoints, raise the front of the car 0.25" and the rear 0.2", re-install the rear bar, and fine-tune from there. It will be much better than it is now.

thank you all so much. Cant wait to try this!

Best post I've read in a long while. I wish I could give two pos cats for it.

https://media.makeameme.org/created/...ive-ywbqwk.jpg