Changed springs what should I expect?
 

Hey all,

I had 8/6 F/R springs and changed out the rears to 7's. Now that I am at a 8/7 ratio, what should I expect for change in my steady state corner handling? Will it be significant or just a slight change?

As an FYI, currently I have slight steady state understeer with my old spring rates and was looking to evenly balance the car. Other than that, the car seems set up very well now.

We don't have to go into discussions beyond this as I have dug and dug and done a very good job of eliminating many issues including my steady state understeer. This is now fine tuning.

thanks,
Ben

In theory that should translate to reduced understeer/increased oversteer, assuming that the rates aren't too high. I don't know what a '8' spring rate equals too in ft/lbs so I don't know if maybe your overall setup is too stiff or too soft with the information provided.

Probably means 8k up front, 7k out back.

6k/mm ~ 335lb/in
7k/mm ~ 390lb/in
8k/mm ~ 450lb/in

Xkg * 2.20lb * 25.4mm = lb/in

I assume this is an FC? 390# seems a little stiff in back given the fronts. What swaybars are you running?

Yes FC.


I am running stock front sway and no rear. Again, I am happy with this so don't want to change. This is about fine tuning. The only thing I would do beyond this point is to make the stock bar adjustable. However, I don't want to go there as I want to talk on what I should see by going from 8/6 KG to 8/7.

Thank you,
Ben

Hey,

Sorry, I can't quiet parse that sentence. If you are happy and don't want to change, then why are you changing?

To me, a 16% increase in spring rates is not "fine-tuning". Adjusting tire pressures is. But that is not really part of the discussion.

In any case - with stiffer rear springs you should see a back end that is more prone to oversteer. But as in everything - it depends. What type of tires are you running? What bushings? What shocks/struts? Did you do the DTSS elimination? What are your camber settings f/r?

It's all a system, and a complex one at that. I am by no means an expert, but trying to reduce understeer by increasing the rear spring rates does not seem to be the best approach. I would be more prone to look at sway bars and camber settings. An 8/6 f/r spring ratio seems to work for a lot of people on the track, so I keep thinking that you need to look elsewhere.


-bill

Bill,

To correct my statement, I don't want to focus on other things beyond springs. The reason being is I have already changed bars (front, rear and stiffnesses), pressures, shock settings, DTSS, toe, camber, bushings, braces, tires and have come up with a combo that gets me as close to steady state neutral as possible.

I also felt that changing the rear spring would not be "fine tuing" but it was the only thing left to do in my analysis since softening the front bar even more did not seem like a good option.

Ben

I'd consider ditching these Xk springs and go to a quality Hyperco or Eibach where you can buy them in steps of 25lbs... 25lbs/in is a noticable rate change... 55lbs/in is significant if you were close to happy before.

Hey Ben,

No problem - I certainly didn't want to come across like I'm putting down your efforts. I just wanted a little more info on what else you had in your setup.

One of the challenges with the FC suspension setup is finding the proper compromise between the McPherson struts in front and semi-trailing arms in back. From what I have seen, read and talked to others about it is very difficult to get a truly "neutral" handling car and when it is neutral it may not be the best setup for getting through the corners quickly.

One of the primary issues is that the McPherson's lose camber under bump. This is compounded by the fact that we want to drop our ride height but can't (due to race class/budget) relocate the lower suspension points to compensate. So we lose a lot of camber - which can result in understeer. To correct for this, many people (incl myself) run a heavy front sway bar to try and reduce roll in mid-turn.

So it's kind of counter-intuitive. You need to stiffen up the fronts a bit to reduce understeer. Kind-of. It's a compromise.

Getting power down to the rears is the other challenge. If the rears are too stiff, you may experience oversteer on turn exit. So you have to keep them a little soft. Which doesn't help your understeer problem in the front, but hopefully by that point you are transitioning weight rearward and gaining a little camber back in the front which will help keep that in control.

So, I'm facing the fact that I'm going to get understeer, I'm probably going to get oversteer, and I have to pick the balance. For me, getting power down a little sooner is more important, so I'll suffer some understeer at the initial turn in. That will mean that I have to enter the turn a little slower but if it lets me come out faster then it's a win.

So, a basic track setup that seems to work well for many people is:
1) a 8/6 (400#/275# in my case) spring ratio.
2) a big front sway-bar (the RB bar seems a popular choice)
3) remove the rear bar.
4) lots of static neg. camber in front, a little less in the rears. (-2.5/-1.5 in my case)

This seems to be a good place to start and you can adjust and tune/tweak to your preferences. Certainly different drivers prefer different setups and no one combination works for all. It all about driving style and compromise. But the reason I bring this all up (and have sat here and typed all this in) is that you seem to be thinking about changes that will possibly make worse the things you are trying to correct for. I just wanted to point this out.

YMMV, void where prohibited. The opinions expressed herein reflect only my own limited experience. Improper application may cause itching, rash and spontaneous combustion. Please consult your physician. Do not induce vomiting.

..and have a happy Thanksgiving. :D

-b

Interesting as you have what I USED to have. Granted my apex acceleration was way beyond my competition with the apex understeer I had. I still have my RB front bar, will NOW always keep off my rear bar, still have my 6 rear springs and have very similar camber settings.

I just "feel" (kinda liberal I know) that if I am neutral through the turn, I can be overall faster inbetween corners.

In the end, if I don't like what I see, I will convert back. I just have hear of other FC's with stock front bars and spring ratio closer to 8/7.

I will report back when I get back from the track after this weekend.

Ben

OK back from the track.

Changes made:

8/7 springs from 8/6
Upped rear tire pressure from 31 hot to 36 hot
Rear toe in went from 1/8" to 5/16"

Before I had some understeer at the apex and the rear tires were never working as hard as the fronts as indicated by a pyrometer. After the above changes, the rears are working a bit harder than the fronts and I have just the SLIGHTEST bit of understeer. Very happy with how things have turned out.

Glad you got what you wanted... but which of the three things you changed did it? :-)

That is easy: springs.

I again was at the track and was able to push it to the limits. Very slight oversteer at apex only after going faster than I have ever been in that car. Tire pressures were about 40 PSI front / 38 PSI rear with the same toe settings. The car is almost there with neutral at apex. I cannot get it to understeer/oversteer upon corner entry which is a good thing.

The only things I am looking to do is get on the gas more after apex. If I get on it early, it seems to want to oversteer.

What tires are you running and what does the MFR recommend as pressures for your vehicle weight? For that matter, what is your weight and power output?

Also did you play with your damper settings at all to go with the new springs?

Well, Nitto on the NT-01's doesn't do a good job of giving details. I understand that 40 PSI hot is considered optimal, as referenced by Nitto themselves on the tech line.

My weight, with driver is 3050 lb and output is 400+ HP.

Yes I played with damper settings to completely eliminate transitional understeer/oversteer issues. They did need to be adjusted pretty significantly to accomodate the new springs. Any more adjusting and I will have to revalve.