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Spring rate help?

So, this is an image a guy shot of my car during the R4C event that's interesting. Look at the inner rear tire here: this is shortly after turning in

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Old 08-12-2014, 08:40 AM   #1 (permalink)
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Default Spring rate help?

So, this is an image a guy shot of my car during the R4C event that's interesting. Look at the inner rear tire here: this is shortly after turning in to the left. I'm mostly likely already on maintenance throttle here given it's T16 (Sugar):



My tire wear has been pretty even at all four corners on the RS3's, but the above is on slicks. With the slicks, the rears are wearing more on the inside and leaving an edge of less-wear at the outside (as if too much negative camber). This pic seems to explain why.

The outer wheel lays down flat, but the inner wheel is nowhere close. (And yeah there's a little of that in the front, too, but it doesn't seem to be enough to dramatically affect tire wear in the net of a lap). I'm inclined to think the camber's fine if the outside tires are doing the right thing, and that getting the inside tire to behave is a matter of suspension...

I didn't make any suspension changes when switching tires, and even on the RS3's I know my springs are kinda weak. The easiest thing to experiment with (and what I should have thought to play with that day) is to stiffen up my damper settings and see if that helps, within reason (but I do need the dampers to move; I tend to run over inside kerbing intentionally a lot!).

I think the real change that's warranted here, though, is to switch to a much stiffer spring rate to help keep the tires pushed down flat. Does that make basic sense here, or should I make other changes first?

The current coilovers are JRZ RS1's (true type in the rear, single-adjustable), and the spring rates that came with them are:

Front: 650 lbs/in (~11.5 kgf/mm)
Rear: 500 lbs/in (~9 kgf/mm)

Like I said, they seemed a little soft for a full-time track car even on streetable tires. What would a good target guestimate set of springs rates be to try out to work better with race slicks (while hopefully not being totally undrivable on the occasion I run some streety tires on the car, or run race wets in the wet)?
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Old 08-12-2014, 09:22 AM   #2 (permalink)
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Old 08-12-2014, 09:30 AM   #3 (permalink)
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Your spring rates are stiffer in the back then front?
Also, what is your sway bar and alignment settings like?
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Old 08-12-2014, 09:48 AM   #4 (permalink)
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I have 16kg front and 8 kg rear and it's pretty good on AD08R and Cup 2, thinking about 18kg and 10kg or more on slicks tho.
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Old 08-12-2014, 09:59 AM   #5 (permalink)
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Originally Posted by clintfocus View Post
Your spring rates are stiffer in the back then front
Oops. Yes, I think I copied them backwards. I flipped them around in the top post now.

Quote:
Also, what is your sway bar and alignment settings like?
I'm on Hotchkis sways on both ends, with the rear currently set at its softest setting (because that worked best for rear-end stability on the street tires - but then again I haven't re-evaluated that in a while, and my driving has improved and changed a lot since then. Perhaps the problem was more me than the car ). I've been hearing the ideal is to go to weak or non-existent rear sway and stiffer rear springs instead.

The other suspension components are stock other than SPL's front upper control arms for camber/caster adjust. Front is in the ballpark of -2.5 camber and 7 in whichever is the only reasonable direction on caster, I think. I set it at home with one of those cheap kits, and it's been a while, I should probably go re-measure and adjust sometime. I left the rear alone at stock-ish settings (with the changes from the car lowering ~3/4" or so), so I think it's gotta be around -2 camber there?

I should start writing these things down when I measure them heh, it's been months.
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Old 08-12-2014, 10:04 AM   #6 (permalink)
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Originally Posted by wstar View Post
Oops. Yes, I think I copied them backwards. I flipped them around in the top post now.



I'm on Hotchkis sways on both ends, with the rear currently set at its softest setting (because that worked best for rear-end stability on the street tires - but then again I haven't re-evaluated that in a while, and my driving has improved and changed a lot since then. Perhaps the problem was more me than the car ). I've been hearing the ideal is to go to weak or non-existent rear sway and stiffer rear springs instead.

The other suspension components are stock other than SPL's front upper control arms for camber/caster adjust. Front is in the ballpark of -2.5 camber and 7 in whichever is the only reasonable direction on caster, I think. I set it at home with one of those cheap kits, and it's been a while, I should probably go re-measure and adjust sometime. I left the rear alone at stock-ish settings (with the changes from the car lowering ~3/4" or so), so I think it's gotta be around -2 camber there?

I should start writing these things down when I measure them heh, it's been months.
I am not Mr. Track but it seems to me that most people suggest stiff front sway soft rear sway. OR...is that just for autocross?
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Old 08-12-2014, 10:10 AM   #7 (permalink)
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Quote:
Originally Posted by Arrvaxx View Post
I am not Mr. Track but it seems to me that most people suggest stiff front sway soft rear sway. OR...is that just for autocross?
His Hotchkis is the most stiff front bar available, but the rear is a bit stiffer than stock tho.
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Old 08-12-2014, 10:21 AM   #8 (permalink)
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Get the front as stiff as you can - you probably won't over do it. We're running between 1000 - 1200 lb/in front springs (900-1000 in the rear) with a custom swaybar made from .120 wall roll bar tube and the front still rolls over more than we'd like. See pic:

Hotchkis is the stiffest off-the-shelf bar that I know of tho, so you're left with just upping the spring rates.
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Old 08-12-2014, 11:02 AM   #9 (permalink)
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Don't run the rear Hotchkis, way too stiff and most likely contributing to the inside rear tread lift. Go back to stock rear and see how it goes
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Old 08-12-2014, 11:51 AM   #10 (permalink)
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Yeah, actually another local forum member here was going to sell me his stock rear bar, but I dropped the ball and forgot to follow up because right after that my engine blew up and everything else went on hold while I dealt with that Maybe I'll try that first and see how it goes next event (and up my dampers a bit too). And then work on upping the spring rates a little later and see how they pan out with different tires and in the wet, perhaps start at something like ~900 and ~800 lbs/in, or whatever values in that ballpark I can locate in matching springs.

Thanks for the input guys
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Old 08-12-2014, 12:44 PM   #11 (permalink)
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Quote:
Originally Posted by wstar View Post
Yeah, actually another local forum member here was going to sell me his stock rear bar, but I dropped the ball and forgot to follow up because right after that my engine blew up and everything else went on hold while I dealt with that Maybe I'll try that first and see how it goes next event (and up my dampers a bit too). And then work on upping the spring rates a little later and see how they pan out with different tires and in the wet, perhaps start at something like ~900 and ~800 lbs/in, or whatever values in that ballpark I can locate in matching springs.

Thanks for the input guys
Yeah going back to stock rear bar would be the first thing I try. Its cost effective and I know for sure a track Z shouldn't have that bar back there lol
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Old 08-12-2014, 01:05 PM   #12 (permalink)
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I run 1000 lb fronts and 550 lb rears and thats not enough spring for slicks. You are way undersprung upfront. low front spring rate allowing rear to lift like that.

We are going to 1100 front and 700 rear maybe more! I drove on streets for couple years with 1000 lb springs and JRZ coilovers. Was downright comfy.
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Old 08-12-2014, 01:51 PM   #13 (permalink)
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I run 1000 lb fronts and 550 lb rears and thats not enough spring for slicks. You are way undersprung upfront. low front spring rate allowing rear to lift like that.

We are going to 1100 front and 700 rear maybe more! I drove on streets for couple years with 1000 lb springs and JRZ coilovers. Was downright comfy.
Really? I'm DDing my new 2 ways that just came in, 1000 fronts and 670 rears I'll figure out tomorrow I guess.
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Old 08-12-2014, 02:09 PM   #14 (permalink)
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Would agree with all the above. The rates are low. In the pic, the front right is rolling over(as is probably the rear), and the rear sway is lifting the rear left.

Clint's suggestion is definitely the fastest, least expensive change though. Long term I would look at something more like 16kF/10KR if you otherwise like your current setup.
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Old 08-12-2014, 02:20 PM   #15 (permalink)
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I was told by the company I bought my 2 ways from that the front and rear rates need to be closely matched for even balance. Like if you need a harder front you might also need to step up your rear. He advised to stay within a 5-6k range unless you're a drifter then it changes. Anyone else follow this rule?

I see Shamu is at 8k difference now but would like 7k and bkleeman is within that range.
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