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#1 chev z

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Posted 28 September 2008 - 08:15 PM

Firstly my Z is a 260 2+2[v6 chev motor] with lowered king springs, koni adjustable shocks,1/2 roll cage, strut bar , rear 20 mm sway bar and 26mm front sway bar set in medium position.I am running 15 x 7 inch rims with soft kumho front and med. rear semi slicks.I tried soft front with stiff rear ,then stiff front and soft rear on konis with very little cornering difference.Hopefully someone with race setup experience can help me overcome extreme front tyre scrubbing, due to car wanting to plough straight ahead when cornering and advise me on front  end wheel set up in conjunction with the suspension that I have or should have. Seeking your race setup knowledge, thanks to all that answer....Steve

#2 stevo_gj

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Posted 28 September 2008 - 08:29 PM

Is that sometimes called understeer? I think if you used the search function on this forum you would find a bit of info.

Good luck,

Steve

#3 chev z

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Posted 28 September 2008 - 08:51 PM

Stevo, tried your suggestion couldn't find much info on wheel camber, toe in or out, tyre pressure[I use cold 30 psi , hot 35psi approx.] ,spring  poundage.....just remembered I have 4 degrees toe in on rear .I will keep searching using different phrases...thanks

#4 Glen

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Posted 28 September 2008 - 08:59 PM

Ash races Zeds and should be able to help you out.

#5 chev z

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Posted 28 September 2008 - 09:18 PM

M..S..Bluz, do you know Ash's username,I was told toe in on rear and toe out on front [my car is running 2 degrees toe in , front]

#6 Hunter

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Posted 28 September 2008 - 09:50 PM

Generally harder shocks in the rear will make the car OVERSTEER. (back end slide)

Harder shocks in the front will make the car UNDERSTEER. (front end slide.)

You want your car to understeer as this is easier to correct while driving than oversteer.

Zeds naturally understeer I think the weight distrubution ratio is 47% rear 53% front. (someone please correct me if I am wrong.) This would be different with your setup.

Try your hardest setting in the rear and the softest setting in the front. Also probably loosen that front swaybar up it may improve your conering.

Otherwise get used to how the car is driving now and compensate with your driving technique.

Scando does circuit racing here in Tassie. Scando is his username.

http://www.viczcar.c...pic,2662.0.html <<<<<<<<CHECK THIS THREAD OUT

I FOUND THIS AFTER A QUICK GOOGLE SEARCH
http://www.thorneymo...ensionsetup.pdf

#7 Lurch ™

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Posted 29 September 2008 - 07:24 AM

Perhaps people with a REAL idea about compettion car suspension should post.
The internet is already full of enough BS already...

I'll post some info tonight after work.
In the mean time get books writtten 'Carol Smith' - that'll set you in the right direction...

#8 620Z

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Posted 29 September 2008 - 12:21 PM

Ha Ha go Lurch!.
Steve this is a bit of trial and error since everyone's car is slightly different. Especially yours with the V6. But to me it sounds like, apart from messing around with spring rates and shockers you need to look at your Camber & Castor. I am also tipping your tyres may not be up to it as well.
Some people have drilled out the top of their strut tower and been able to slide them about 10mm closer to the motor. This would help the handling as a cheaper option. Also you most likely get bumpsteer. If this is the case like 97% of Zeds then this will also effect the handling of your car when turning into a corner. Heaps of varied fix's here depending on the cash you have. there might be a picture or two under my ZZZ8 that could give you some ideas. If not Lurch might be able to help with some more technical info.

#9 zr240

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Posted 29 September 2008 - 03:53 PM

hi steve

I raced a very well handling zed for quite a few years (hopfully will race again) and as Lurch said there is alot of BS all over the place. I have alot of suspension/ handling books and have read pages of info but really to give you a correct and usefull piece of information on getting your car to stop understearing I would have to have a good look at the car. There are soo many things on an old zed (infact when the zed was new it apparently was a big understeerer:)) cause it to understeer. Hey for all I know it could be your right foots prob :)

Really though I thing Craig (or Lurch) would probably be able to give you the best advise because he has a v8 zed and does a bit of track work aswell.

My car always had super sticky wide tyres and not that much power so it really stuck like glue to the track so I did muck with the handling a whole lot:) Hopfully with my new powerplant I will have to much power and have to work on getting more grip and handling out of the car.

Ash

#10 Glen

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Posted 29 September 2008 - 05:13 PM

M..S..Bluz, do you know Ash's username,I was told toe in on rear and toe out on front [my car is running 2 degrees toe in , front]


whoops yer i got it back to front lol

#11 Scando

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Posted 29 September 2008 - 05:57 PM

The first thing I would try is getting some negative camber on the front as some others have suggested.  This should help turn in and help with your tyre wear.  I have my lower control arm mounting points re-drilled about an inch up and out from the original positions.  This gives the car a bit of negative camber but it still needs more.

Sounds like your front swaybar is adjustable so maybe trying softening it up a bit.

What sort of diff are you running?

Let us all know what you try and what you find does and doesn't work.

#12 Hunter

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Posted 29 September 2008 - 06:29 PM

Perhaps people with a REAL idea about compettion car suspension should post.
The internet is already full of enough BS already...

I'll post some info tonight after work.
In the mean time get books writtten 'Carol Smith' - that'll set you in the right direction...


I hope that comment was not aimed at me LURCH. I was just trying to help, that is why I suggested Scando.

#13 zr240

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Posted 29 September 2008 - 06:48 PM

Hi Scando

Dont think Lurch was having a go at you as I think what you said is spot on :)

Not exactly sure who he is having a go at, I thought he was just generalizing as there are alot of people online(and offline) who think they know alot and have often never actually done any real work on cars :)

Look forward to reading what Lurch posts as I think we can pool all our different experience together and sus most probs out :)

Ash

#14 Hunter

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Posted 29 September 2008 - 06:50 PM

Yeah she is all cool.

#15 Zeddophile

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Posted 29 September 2008 - 06:52 PM

Hopefully someone with race setup experience can help me overcome extreme front tyre scrubbing


Which part of the tyre is scrubbing?  The whole width of the tread, the inner, the outer?  If its the outer half really wearing badly, as others have already said negative camber would be a good starting point.  

I found on my Alfa with 1.7 degrees of negative camber on road tyres, my front tyres wore very evenly around Sandown, despite the very standard suspension leaving lots of bodyroll and a touch of understeer to contend with.  However, on cars we set up to run 'R compound' (road legal race rubber) tyres I think its more like 2.5-3 degrees.  Then if running radial slicks, I believe the camber figure is somewhere between road tyres and 'R' tyres - not sure why that is.  You will almost always get wear on the very outside edges of all tyres though, regardless of suspension settings.

End of the day, its not that relevant to what you are doing other than as a guide figure - not sure what the standard Z front camber is, but I'm guessing not a lot.  I would think that 1.5 degrees negative camber would be a minimum figure on your semi slicks, but thats just my thoughts on what I'd use as a starting point if I were doing it.

Have you tried varying the tyre pressures in the front a few psi either way?  It sounds like you are in the right range for those tyres, but some people/cars find 5 or even 10 psi one way or the other works better for them....

Another point is - have your roll centres been corrected for the lowering (and does it require that on a Z)?  This makes a huge difference on an Alfa GTV - raising the front roll centre and lowering the rear one makes the handling improve vastly.  The Alfa ones aren't well located at factory height, and once lowered, become much worse.

Your best bet is probably to call Top Performance in Vermont (don't have the number to hand), I'm of the belief they have set up more than a couple of zeds for various event types, and will probably have much better idea of what are the important points to address with a zed, and more specifically to help iron out your problem.  From dim memories of my chats with them, they commented about roll centres when lowering.  Either way, they have set enough cars of all types up, their thoughts would be invaluable, and I've always found them helpful.

#16 DevilZ

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Posted 29 September 2008 - 07:24 PM

Firstly my Z is a 260 2+2[v6 chev motor] with lowered king springs, koni adjustable shocks,1/2 roll cage, strut bar , rear 20 mm sway bar and 26mm front sway bar set in medium position.I am running 15 x 7 inch rims with soft kumho front and med. rear semi slicks.I tried soft front with stiff rear ,then stiff front and soft rear on konis with very little cornering difference.Hopefully someone with race setup experience can help me overcome extreme front tyre scrubbing, due to car wanting to plough straight ahead when cornering and advise me on front  end wheel set up in conjunction with the suspension that I have or should have. Seeking your race setup knowledge, thanks to all that answer....Steve


Hi Steve,
I was just curious as to what differential you are using in your car. Also when you talk about your car wanting to plough straight ahead when cornering, is this when you are only on the throttle, on the brakes, rolling or does it do it in all 3 cases?
I was also wondering what width tyres you are running front and back? Kumho's aren't a very good tyre in general and they will wear very fast. I've seen a street driven Evo 7 go through a new set of Kumho Escta's in 5,000kms and those were warn to the wires.
Your tyre combination and size will make a huge difference to what you want to achieve. Semi-slicks are also only good if they get to the right temperature range, which i'msure you already know. If there not hot enough you will spear straight on every time......



#17 Scando

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Posted 29 September 2008 - 07:51 PM

Hi Scando

Dont think Lurch was having a go at you as I think what you said is spot on :)


lol, I didn't say he was, I think that was hunter.

Have you tried varying the tyre pressures in the front a few psi either way?  It sounds like you are in the right range for those tyres, but some people/cars find 5 or even 10 psi one way or the other works better for them....


That's another good point.  I find changing my pressures by as little as 1 psi can make a huge difference in the longer races.  See if you can find other cars running the same tyres at your next track day and ask what tyre pressures they're running.

Might also be worth trying some different tyres.  I run Bridgestone RE55S which wear quite well.  Dunlop's are as good as you'll get but wear quickly and are expensive.  Toyo's seem to be good value for money.

#18 Lurch ™

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Posted 29 September 2008 - 09:14 PM

I need some more info, 'Chev Z':

What is the spring rate? As the Zed has near enough to a 1:1 ratio the spring rates will be more or less the same as the wheel rate. Lowered King springs are fairly soft so I'd be looking to go up in rate all round.
What are the tyre temps at after a session: outside, middle & inside of the tire <- this info is important.

As a very broad guess, I I'd say you need more front camber & a possible increase in castor.

The Khumo V70A's are a very soft compound R-spec tyre. Hence they reason they wear quickly.
They are PERFECT for Super Sprints because they have a fast heat up time.
BUT if used with incorrect suspension setup, they WILL degrade very quickly.
Also comparing an road car to a track is just plain silly...
DevilZ, Have you used them yourself? Or are you just going off what you've seen???
The setup of a 4WD Evo is a completely different kettle fish to a Zed...

People, IF YOU DON'T KNOW WHAT YOU ARE TALKING ABOUT - DON'T POST! >:(
I DO NOT want to see in-accurate information posted on this site.

#19 Glen

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Posted 29 September 2008 - 09:23 PM

Also comparing an road car to a track is just plain silly...
DevilZ, Have you used them yourself? Or are you just going off what you've seen???
The setup of a 4WD Evo is a completely different kettle fish to a Zed...

People, IF YOU DON'T KNOW WHAT YOU ARE TALKING ABOUT - DON'T POST! >:(
I DO NOT want to see in-accurate information posted on this site.


oh my thats gold!  :o


Should we get pre-approval before posting from now on....

#20 Zedman240®

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Posted 29 September 2008 - 09:28 PM

From memory lowered King springs are only around 180-200 Lb/in. A powerful tool to take with you next time Chevz is a infra-red pyrometer to measure the temps of the tyre as Lurch said from the inside, middle and outside edges. They should all be within a couple of degrees of each other. I remember checking one zed's tyre temp and they were out by about 12-15 deg C of each other (hottest was the inside) which meant too much negative camber. Those pyrometers used to cost about $5-600 now Jaycar sell them for about $100. Only when you do that will you know whats happening with your suspension. I'd probably go up in spring rate also; I'm using Kings 300Lb/in on all corners and that seems ok for most events.




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