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Suspension Setup - Race


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#1 Missinglink

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Posted 13 June 2015 - 01:17 PM

Hi Guys,

I am in need of some advice for setting up suspension on my car from scratch, but first things first, specs below:

I have a 1972 240Z with a 302 windsor and 5 speed manual (dont shoot me!). I am running the full Arizona Z suspension setup including the big brake kit and have a half cage and extended sub-frame connectors. I am running on 235/45/17 bridgstone R comps

My alignment settings at the moment are:

Front Castor = 0.00 (L&R)
Front Camber  = 2.01 Degrees (L&R)
Front Toe = 0.08 (L&R)

Rear Camber = 2.4 (L&R)
Rear Toe = 0.00 (L&R)

Now! I am finding a finding a few issues on the track:
1) high speed braking feels very (twitchy) and the car squirms at the rear
2) Mid corner steering feel is very low, as in i am finding it difficult to figure out how much grip i have mid corner (if this makes sense)

I have 250lb springs front and rear and the shocks are set to about 6 clicks from the hardest settings (bump and rebound adjustment in one).

I was just wondering if anyone has any suggestions/settings or is using the same gear so I can work out where to start adjusting.

Thanks in advance

Zak

#2 Lurch ™

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Posted 13 June 2015 - 01:52 PM

Hi Guys,

I am in need of some advice for setting up suspension on my car from scratch, but first things first, specs below:

I have a 1972 240Z with a 302 windsor and 5 speed manual (dont shoot me!).


Well I'm not really into kicking a bloke while he's down...

I am running the full Arizona Z suspension setup


There's your first problem.

including the big brake kit and have a half cage and extended sub-frame connectors. I am running on 235/45/17 bridgstone R comps


Bin the brakes as well - you'll warp the rotors & cook the calipers.

My alignment settings at the moment are:

Front Castor = 0.00 (L&R)
Front Camber  = 2.01 Degrees (L&R)
Front Toe = 0.08 (L&R)

Rear Camber = 2.4 (L&R)
Rear Toe = 0.00 (L&R)


Change it to:

Front Castor = 5deg positive - the more the better. (L&R)
Front Camber  = Start at 3.5 deg negitive & adjust from there, via tyre temps (L&R)
Front Toe = 1 mm toe in (L&R)

Rear Camber = 2.4 (L&R) probably too much, but what are the tyre temps reading?
Rear Toe = 1 mm toe IN (L&R). Toe out makes IRS cars nervous in the rear.

Now! I am finding a finding a few issues on the track:
1) high speed braking feels very (twitchy) and the car squirms at the rear

You require more rear toe - see above.

2) Mid corner steering feel is very low, as in i am finding it difficult to figure out how much grip i have mid corner (if this makes sense)

Not enough Castor - see above.

I have 250lb springs front and rear and the shocks are set to about 6 clicks from the hardest settings (bump and rebound adjustment in one).
I was just wondering if anyone has any suggestions/settings or is using the same gear so I can work out where to start adjusting.


The China damper insert is junk in the AZC setup- you'll either get full soft or full hard with nothing in-between. Throw them in the bin & buy some MCA's.
As a starting point I suggest you install 350lbs springs in the front & go from there.
Leave the 250lbs springs in the rear for the moment, till you get the front end behaving like you want.

Thanks in advance

Zak


No problem, but I'm betting you won't follow my advice...

#3 MaygZ

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Posted 13 June 2015 - 02:40 PM

Now Lurchos, don't be so negative.  Your advice may very well be followed to the letter.

I'm not going to refute or challenge anything you have said above - but rather concur with your solution with regard to the squirmy braking and the lack of feel mid-corner.

Too much weight is being moved forward, so increasing the spring rate at the front will help keep rubber on the ground at the back.  Rear toe in will also help keep more rubber on the road during braking.

A little pos caster on the front will help turn in.

I'm sensing that your mid-corner feel issues are due to initial understeer which reduces your desire to throttle on early (read rolling through the apex) allowing the tail to 'float' instead of being planted by throttle.  Fix your turn in and then see where you can throttle on.

One thing to remember with steering and suspension set up - it's all robbing Peter to pay Paul.  Improving one thing will reduce something else.  Having said that: the numbers that you have put up leave plenty of room for improvement (as per Lurch's comments)

I have no experience at all with the AZC inserts/struts so I can't comment on them - but I know Lurch has so I trust his opinion on this matter.

Good Luck

#4 PeterAllen

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Posted 13 June 2015 - 02:55 PM

You haven't stated what balance bar setting and m/c(s) you are using - or a proportioning valve setting. I could comment further but I see you are not a donating member!

#5 Missinglink

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Posted 13 June 2015 - 05:01 PM

Righto! Thanks for your input everyone!

I think i will start at the cheaper end of your suggestions Lurch! ie the alignment settings, and work from there....I have already warped the rotors once and upgraded them to something that doesnt warp. In regards to my 'racing' the car is not a full time race car, so I dont think a full brake change is worth the hassle at this stage. I will no doubt stick with the current dampers as it becomes a costly excersise to change everything all at once. It is interesting to hear your thoughts on the AZC gear, i have not heard much from people using his gear in anger before.

The MCA suspension is on the wish list already....

In regards to other questions, i am using a 15/16th MC and i think the front sway bar is 22mm and the rear 19mm.

#6 Lurch ™

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Posted 13 June 2015 - 05:08 PM

Update your location to, cocko...

#7 PB260Z

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Posted 13 June 2015 - 05:10 PM

I could comment further but I see you are not a donating member!


Good Point  ;)

#8 Lurch ™

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Posted 13 June 2015 - 07:02 PM

The MCA suspension is on the wish list already....


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#9 Scando

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Posted 16 June 2015 - 01:18 PM

Change it to:

Front Castor = 5deg positive - the more the better. (L&R)
Front Camber  = Start at 3.5 deg negitive & adjust from there, via tyre temps (L&R)
Front Toe = 1 mm toe in (L&R)

Rear Camber = 2.4 (L&R) probably too much, but what are the tyre temps reading?
Rear Toe = 1 mm toe IN (L&R). Toe out makes IRS cars nervous in the rear.


Agree with what Lurch has said above.  I prefer a little toe out on the front rather than toe in but given the care feels unstable at the moment, the toe in should be better.

The only thing I will add is to do one step at a time so you know the difference each change made.  Start with the alignment setting and see how it feels.  If that doesn't fix it, move on to the springs and shocks.


#10 Missinglink

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Posted 17 June 2015 - 05:18 PM

.

#11 Missinglink

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Posted 17 June 2015 - 05:22 PM

So,

Had the wheel alignment adjusted today by a race guy here in Perth,

Front now running 3 degrees neg camber, 2 degrees pos castor, total 0.9mm toe in. Rear now 3mm rear toe in, 2.25 deg neg camber. Cant run much more castor as running out of space in the wheel arch apparently (if that makes sense).

So now to get it to the track and see where to go from here.

#12 PZG302

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Posted 17 June 2015 - 06:46 PM

Cut the guards, they will only need a little trim of a few mm depending on what wheel tyre combo you are running.

I had to trim about 20-30mm from mine to fit 240/650/18 slicks on a 8 inch rim with around -2mm offset. Got me all the castor i wanted/needed.

#13 Missinglink

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Posted 17 June 2015 - 07:05 PM

Cheers! You dont happen to have any pics of the area you trimmed do you?

I am not sure if the issue is related to the rims I am running, 17*9 with a +17 offset (R32 GTR). Or if its just normal for a Z?

#14 dat2kman

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Posted 17 June 2015 - 07:20 PM

Put a bit f steering lck on, get someone, heavy, to stand in/on engine, to simulate suspension compression, you'll then see what needs trimming, it wont be much, just the very lower front edge.

#15 Missinglink

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Posted 17 July 2015 - 09:24 PM

So, quick update, finally got the Z to the track.

Suspension settings are a huge improvement! much better turn in and now i can feel whats happening mid corner, thanks to all suggestions.

Now I just need to work on the shocks and driver.....

#16 Lurch ™

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Posted 17 July 2015 - 10:01 PM

;)




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