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Looking for some advice on suspension set up for autocross

Old 04-24-2017, 04:49 AM
  #1  
cbax
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Default Looking for some advice on suspension set up for autocross

Made some big changes over the off season and had my first event of the season yesterday with the SCCNH club. We managed to get 1st and 3rd in a class of 16. SCCNH's Street Mod class = SP and SM automatically paxed and bumped. But we sortof fought setup issues all day and I would like some feedback.


Quick specs:
2004 G35 track pack in ESP
16/14k (stock rear location) FA dreadnought Pro 2-ways
Large front sway bar, currently no rear sway bar
OS Giken diff
Hawk HP+ (blah) pads
275 RE71-Rs for the next 2 events, then 315 Hoosiers (ended up at 35/32 yesterday for pressures)
seats, shorai battery, no ac, single exhaust
Car makes 260whp on a "low reading dyno"


Problems:
- Front end bounce
- wheel/fender contact (too low in the front)
- corner entry push, decent mid corner grip...but feels like it could be better.
- hard to hook up on exit (loves to drift)
- brakes too grabby


This is my first double adjustable set up. Started the day at 50% on all Compression and Rebound settings. Tightening up front rebound made the bounce less severe. Loosening up rear compression made it hook up a little better. But I didn't go too crazy with either as the car was decently competitive and I wanted to make sure it wasn't just us. Literally no changes other than pressures for the first 4 runs. Then had 7 in the afternoon that we made adjustments in between each one. Do we keep going up in front bump or keep going up in rebound? Or both? What should happen to rear settings as front changes? Go up equal amounts to keep the balance the same?


The coilovers have independent height adjustments so I'm pretty sure we aren't hitting the bumpstops. But I am going to raise it up in the front anyways.


Ferodo DS2500s have been ordered. I'm putting front and rear in now. After I feel like the suspension is balanced as good as it will get, we may experiment with HP+ in the rear...maybe.


Sway bars. I feel like if I toss the rear sway back in, we will get that entry and mid corner grip back. But it's already really loose on exit. I'd hate to make that worse. Can the loose exit can be tuned out with shock tweaks if we add the bar? What about just tossing a stock front bar on?


Should I get some different rate springs on the way?


Attached some pictures of the car. Yes..its obviously too low in the front. Rear comes unloaded at full droop right now (I'm out of preload adjustment on the shock), but I feel like it should be a little lower. Front is coming up 1/2"-1"


any help or advice is appreciated.
Attached Thumbnails Looking for some advice on suspension set up for autocross-18077125_1631033403597659_1215087957559208226_o.jpg   Looking for some advice on suspension set up for autocross-18119082_1631033473597652_3451673662445609066_n.jpg  
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Old 04-24-2017, 04:57 AM
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Alignment specs are as follows

-3.5/-2.5 camber
0/-.15 toe

I ran a little toe out in the front last year. But with us travelling 2.5 hours to events this year, I decided to run 0 front.

The rear camber on one side could not go lower than -2.5 and keep toe in check. I was originally targeting less than -2 deg in the back. And we did that on one side. Then the other wouldn't do it. Car has Z1 street front and rear camber arms. Maybe I need a new technician? He was pretty frustrated towards the end. haha Im getting my use out this lifetime alignment though.

Last edited by cbax; 04-24-2017 at 04:59 AM.
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Old 04-25-2017, 09:35 PM
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Waiting for the BSP master to chime in.

My thought, back off rear spring rate
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Old 04-26-2017, 03:23 AM
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Car isn't that stiff, but sounds like the shocks are not valved for the rates. Do you have a shock dyno?

Front end "bounce" would make it hard for the front to set, grip and turn like it should. I wouldn't be surprised if you are on the bumps in the back, which would make the car crap on corner exit/power down. I'm guessing if there is a bump in the mid turn the car is also junk?
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Old 04-27-2017, 02:55 AM
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Lower the psi in the Re71. I run F28/R26 cold on my setup. I will let the pros talk about suspension setup. I am learning that myself. I do remember a pro making a thread about setting up a BSP 350z...

My specs : For RE71. (I was told by the pro above to much camber for the HoHo's.)
-3.5F / -3R
1/16 out front
1/16 in rear

Also a few locals that have been doing it longer had great success(best borat voice) with the HP+?

Chris
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Old 04-27-2017, 03:14 AM
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The 71's do like low pressures...
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Old 04-27-2017, 04:07 AM
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Thank you guys for chiming in.


I am attaching the shock dyno plots.


Like I said above, we started the day with front and rear rebound and bump set to 50%. We never touched front bump or rear rebound (have to drop shock top mount to adjust).


After doing a little reading, it definitely seems like all problems start with the bounce. if we get it to turn with that issue, we are likely screwing up the rest of the corner. And it seems like that is happening because of a lack of compression and maybe rebound in the front end.


The rear shocks are at the lowest limit (with the reservoir fitting tying up 3/4" of that space). The springs do come unloaded when you jack it up. I may pull one and test articulation to see where the bump stop is. Should I get some helpers on the way? My thought is that rear shouldn't really any higher than it is now though.


My plan of attack for this weekend is to raise the front at least 1/2" maybe more. The front compression is at 12/24. I'll raise that to 20/24. The rear rebound is 12/24. I'll raise that to 16/24. Then I'll easily be able to adjust rear comp, and front comp/rebound during the event.


I will try a lower pressure as well. My starting point of 36/33 was from my notes last year on stock shocks and lowering springs. Things did better once we dropped a couple psi.
Attached Thumbnails Looking for some advice on suspension set up for autocross-20170427_075415.jpg   Looking for some advice on suspension set up for autocross-20170427_075420.jpg  
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Old 04-27-2017, 04:54 AM
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I run 27/26 psi hot on 285 71r's n 11s for even wear. Car is 3100 pounds for reference. You might need to be a couple psi higher for a g35 depending on its weight.
I second that you are probably hitting bump stops on corner exit. Wrap a zip tie around the top of your shocks shafts at the beginning of a run. As you do the run, the zip tie will move down based on how much shock travel you are using. It will be a good indication if you are bottoming out.

also, HPS pads have a lot less initial bite for braking. You may like those more

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Old 05-01-2017, 03:55 AM
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Saturday I raised the front end about an inch, raised the rear about a 1/2" (rear spring is slightly preloaded now at droop), turned up front compression to 20/24, and turned up rear rebound to 18/24. Then started the day yesterday at 32/28 for pressures.

It was fantastic. Bounce is gone. And everything from turn in to exit was awesome. I was .1 off the fastest fender and managed to get #2 in pax behind a st miata and great driver. At the end of the day, I dropped the rear to 27, turned up rear compression back up to 12/24, and turned up front rebound to 20/24. Fastest lap was last run in sprinkling weather and mid 40S temp. It was .2 faster than my fastest in the morning in the Sun and mid 50s.

Only issue was a braking problem in the stop box that happened to me once and happened to my co driver once. It also happened alot last weekend during the bounce. Brakes lock up and then just disappear. Ive got the yaw sensor unplugged to defeat the vcd. And ive never felt a typical pulsing ABS. Not sure what's happening and need to do some research on it. I installed ss lines and bled the system before our first event. I'm still on the hp+ waiting for new pads to arrive.

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Old 05-02-2017, 09:15 AM
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I am also looking at autox suspension setups.

How much better are the koni 3012s vs the Ohlins R&T?

Beside the obvious that one is double adjustable.

My STU build

Enthusiast 350z
Stock except the following:
OSgiken dif
Front Hotchkis Bar
Modified Kinetic A arms
Braille light battery.
Weight: 3176

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Old 05-31-2017, 12:37 PM
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subbed for learning.. good stuff here.
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Old 06-03-2017, 03:22 PM
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cbax
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My issues are pretty much non existent on RE71Rs at this point. Just cranking up the compression and rebound made it 1000x better.


Ran the 315 Hoosiers at a small local autocross 2 weeks ago. Some of the bounce came back, but adding a little more compression up front made it mostly go away unless you just went in too hot. Took FTD and #1 PAX at that event. Codriver was #2 for both.


The Ferodo 2500s made the ABS system happy and have way better modulation and feel than the HP+.


Over the off season, I'll probably send these coilovers in for a revalve and up the spring rate as well, requesting that the valving be on the high side for the new rates.


Running the Hoosiers again tomorrow with SCCNH and hope to refine the setup for the champ tour in 2 weeks at Devens.

Last edited by cbax; 06-03-2017 at 03:23 PM.
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