Please help - handling issues

[LT1-280z]

I’m hoping someone can give me some advice on improving the handling of my Z. Its really not where I want it to be. My car is a V8 conversion with an LT1 and I have upgraded most every area. I have coilovers, Tokico Illumina, sway bars front and rear, AZC wilwoods, VLSD diff with CV’s, 17†wheels with bf goodrich kd 225/45. I take the car to HPDE events and as my skills have improved I have been finding limitations in the handling of the car. At prior events I found the car limited by understeer but generally stable and predictable. In an effort to take it to the next level I added camber plates to the front allowing -1.25 degrees, roll center spacers and lowered the car significantly more. Front struts are BZ3099 and for the rear I replaced the tall 280Z isolator with the shorter front one. At the last HPDE the car’s front turning grip was greatly improved but now the rear is giving up in a bad way the car is somewhat oversteering, feels unstable cornering like the rear is going to go out at any second. Here are the alignment settings

 

Front

Camber = -1.25

Caster = 4.6

Toe =  0.21

 

Rear

Camber = -1.15

Toe = -0.01

 

Scales (with Driver)

Left 50.9%

Front 47.9%

Lf/rr 50.1%

Right 49.1%

 

Tokico’s are set at 5 all around

 

Spring rates

front = 200

rear = 250

 

Any advice is greatly appreciated, I really need to get this sorted I can’t have 944’s and Honda’s lapping me!

[RebekahsZ]

1. Sell me any BZ3099s you have in the MR2 length. (I need one now).

2. Reduce front shocks to 3 and rears to 2.

3. Increase camber to -3 in front and -2.5 in back.

4. Buy a used set of Hoosier R6 245s or 255s off eBay. I don't know why anybody uses anything else. My last set cost $400 for a set of four.

5. Get a driving lesson from cobramatt.

 

Go race!

[RebekahsZ]

Tire pressures: low-like 30 front and 26 rear hot. You will have to let air out as they get hot. My tire pressures go up as much as 10psi from cold to hot.

[jt1]

Better tires will make you faster.  They may or may not improve the balance.

 

More camber F & R, 2.5 to 3.0 if you can get it.

 

Toe the rear in about 1/8".

 

Make sure your LCA's aren't going negative, sometimes that happens with a lowered car.

 

Consider a smaller rear bar, or maybe none at all.

 

When is the car loose?  Entry, steady state, or off?

 

jt

[pureZero]

Just make small adjustments to the rear as you go... As I'm sure you know, oversteer is better than understeer, as long as you can control it. I would actually try to avoid adding a whole lot of negative camber, as it could cause it to oversteer more, if enough is added. I would actually try to soften up the shock absorbers in the back just a hair, personally. You could also try strengthening up the LSD a little bit too...

[LT1-280z]

Wow, Thanks for replying so quickly.

 

As for the BZ3099 I got mine from http://performance.importrp.com/tokico/tokico_shocks_illumina_series/tobz3099/i-526545.aspx

Great price and good folks to deal with.

 

 

I did try the shock setting in the rear down to 3 but it was no better maybe worse. I'll try your recommendation of F3 R2 - its not a good idea to test these things on the street

 

I can maybe get a little more camber on the front - the camber plates are limited. I would have to do control arms to go any further Rear is not adjustable (yet)

 

I'm sure tires would help, but I was getting passed by cars with street tires. I would like to get it working right with street tires first. rather than cover up the balance issue with slicks (btw the guys with slicks were really fast)

 

Hot tire pressures were at 28 front 30 rear, I upped the rear to 35 and it felt a bit better but no where near what it needs to be. yes the pressure goes up about 6 cold to hot

 

I was carful not to let the LCA to go neg. they are about level in the rear so there will be no camber gain there, the front has the spacers so they are still slightly +. I was thinking improving the rear LCA angle might help but its not at all easy to do.

 

I did have questions on the rear bar easy enough to disconnect and try it.

 

When is it loose? It generally feels like is on a knife edge on initiation, but turns in quickly, then mid corner steady state it feels like the rear wants to let go if you even think of trying to go faster. no where near balanced. I remember diving a 924 turbo many years ago, it felt so balanced, push it in a corner and the front and rear slip pretty much even. that's what I want. That will help confidence and with confidence will come speed (of course more driving lessons wouldn't hurt ether)

 

I could see how a little neg toe on the rear could counter the oversteer a bit. I was also thinking of backing out some of the front camber, split the difference, it was pretty much dead 0 before the camber plates so maybe back to -0.75. (just to try to find ballance)

 

If I can get this sorted I will consider slicks (I have a spare set of 16x7 wheels)

 

Thank you all for your suggestions!

Edited August 4, 2013 by LT1-280z

[jt1]

 

 

When is it loose? It generally feels like is on a knife edge on initiation, but turns in quickly, then mid corner steady state it feels like the rear wants to let go if you even think of trying to go faster. no where near balanced.

 

I would unhook the rear bar and try that first.  Cheap and easy.

 

Don't think about less camber front, work on getting more for the rear.  Less front may improve the balance, but ultimately makes you slower.

 

If the LCA's are level with the car sitting still, they may be going negative when the car rolls in a corner.

[LT1-280z]

I would unhook the rear bar and try that first.  Cheap and easy.

 

Don't think about less camber front, work on getting more for the rear.  Less front may improve the balance, but ultimately makes you slower.

 

If the LCA's are level with the car sitting still, they may be going negative when the car rolls in a corner.

 

 

Will try the sway bar disconnect tomorrow.

 

As far as ultimate potential, yes taking away grip in the front won't be as fast as keeping front grip and fixing the rear. But with the imbalance I'm slower now than before adding the front camber.

 

Agree probably going neg in the rear LCA while in corner and will probably get worse with the softer setting on the shocks and disconnected sway bar. How can the rear LCA angle be improved? Front was easy with the spacer.

[mark]

Make the front stiffer and the rear softer. The rear bar as jt1 suggested is the first place to start. Also street tires need more air pressure than you are running. Try 40-42. More rear camber for sure.

[JMortensen]

If the LCA's are level with the car sitting still, they may be going negative when the car rolls in a corner.

Doesn't matter. As Terry Oxandale showed me years ago with this drawing, you won't actually start losing neg camber until the control arm is perpendicular to the strut tube, which I think is practically impossible. He says caster, but meant camber:

http://www.fototime.com/ftweb/bin/ft.dll/detailfs?userid={7DC317B0-8EDB-4B2E-A837-F708D07C9769}&ndx=19&slideshow=0&AlbumId={E19B86F3-5BFB-4733-AF72-09BD805A6F1A}&GroupId={832D28D1-26F8-4E35-B3D1-6BB2152C089B}&screenheight=1050

 

All that happens when the control arm points up is the rate of camber gain changes, and even that isn't a big deal. This post has a diagram of the camber curve on a Z and also talks about something more important, loss of camber due to roll. 

http://forums.hybridz.org/topic/63492-suspension-tech-motion-ratio-unsprung-weight/?p=616174

 

The more tire you have the more spring you need, so if you're talking about going to sticky tires, you'll be running out of spring pretty shortly I suspect. I ran 200/250 on my car for years and ran slicks with it. Even with the camber plates maxed out my tires ended up wearing pretty badly on the outside edge.

[johnc]

Swap the springs front to back and keep the rear bar hooked up for now. You want the car to feel loose mid corner and on corner exit. These cars are steered with the throttle at the limit. From your posts it appears you haven't got it sideways, much less spun. These cars handle best with the back end out a bit it a four wheel drift. I suggest you get used to that knife edge feeling because its the fast way around a track.

[RebekahsZ]

It is cool that each of us has had different advice. Must be a lot of different ways to get to the same place. Johnc, do you still sell any bolt-in camber plates he could buy and install in back while swapping the springs? Achieving your recommended alignment specs was the best "cook book" thing I've done to my car. I was happy with it right out of the box. I've had one pro autocross driver take it around the cones a couple times and one pro driver take it around a big track for about an hour and the reviews have been positive with no complaints. When it was tail happy with street tires, we were able to simmer it down a lot just with changing the tire pressure and shock settings.

[LT1-280z]

Swap the springs front to back and keep the rear bar hooked up for now. You want the car to feel loose mid corner and on corner exit. These cars are steered with the throttle at the limit. From your posts it appears you haven't got it sideways, much less spun. These cars handle best with the back end out a bit it a four wheel drift. I suggest you get used to that knife edge feeling because its the fast way around a track.

 

Oh yes I did spin. 360's across the grass thank goodness I missed the armco. I was pushing it and the rear let go and just kept on going. Usually I can feel it coming on and "play" with it with the throttle but with the current setup it just let go and went around and around.

 

I tried disconnecting the rear sway bar and setting the shocks to F3 and R2 today and it seems better. I can't really test it fully on the street. I will try swapping the springs next. Maybe work on adding more negitive camber to the rear.

 

Jon, Interesting info, I'll certainly will relax on the LCA angle. What spring rates would be a good match for slicks?

 

Thank you all for your suggestions. I'll post my progress.

[JMortensen]

Seems like the fast guys are going 400+ on the springs. The issue is that your tokicos won't handle it, so then you get into other struts and that's a whole other rabbit hole. If you are driving and tracking this car, I'd stick with what you have and disconnect the rear bar as others have said. If you want to go with sticky tires, you'll have a lot of issues to work through.

[johnc]

A lot also depends on the diff you're running. With the Vlsd you're better off running the rear springing softer then the front. The Vlsd does go open or you get a very uneven torque distribution if the inside rear wheel gets very light.

[heavy85]

"and lowered the car significantly more"

 

Not sure what that means but you may want to undo that.  IME those springs can still be relatively fast.  Yes Jon is right once you are getting really serious you will want more but those should work for what you are doing.  Rear toe in is good, very good.  Swap springs.  As light as those springs are I think you need the bars.  I dont run a rear bar but use 425/375 springs.  Get the camber where the tires are happy and I wouldn't use camber to adjust balance.

[tube80z]

You've already got a lot of good advice.  The one thing that would help a lot is if you can find some pictures of the car loaded up in a corner.  These can tell you a lot.  Is the car rolling too much, how is the camber, how does the front look compared to the rear.  One reason you're getting advice to add a lot of camber is two fold.  Not only do the tires need it to get the maximum rubber on the ground but with the soft spring rates you're running the car will roll a lot.  Typically it does this by compressing the outside spring a little and lifting up on the inside spring a lot.  And on a strut car you lose camber at almost the same rate as roll.  

 

One thing that's been done on a few chump cars that might be worth trying is to limit some of your droop.  This will make the car work like you have stiffer springs and could be something you put on at the track.  I would try it first at a lower speed event like an autox before you jump into the deep end on a track at a HPDE.  I'd probably try running around 1 to 1.25 inches of front droop and 1.75 to 2 inches in the rear.  You can try less and see if that helps.  The car will probably change direction a lot quicker that you're used to, which is why I'd try the autox first.  This trick will help to limit the amount of roll the car sees by stopping inside lift and making the car push the outside down for any more roll.  It might make a good compromise if you want to keep the car softer for the street and not reun higher rate springs.  

 

Hope this helps,

Cary 

[LT1-280z]

Thanks Cary,

 

Yes lots of good advice here. I really appreciate it.

 

So far disconnecting the rear sway bar and softening the shocks seems to have really tamed things down.

 

Droop limit makes a lot of sense. Seems like a similar affect as sway bars but centered on the inside and only active when enough roll is achieved.  

 

For this car I do still want it streetable. I've been giving some serious thought to a dedicated track car. Something like a chump car. So I can beat the snot out of it and not worry.  

[LT1-280z]

"and lowered the car significantly more"

 

Not sure what that means but you may want to undo that.  IME those springs can still be relatively fast.  Yes Jon is right once you are getting really serious you will want more but those should work for what you are doing.  Rear toe in is good, very good.  Swap springs.  As light as those springs are I think you need the bars.  I dont run a rear bar but use 425/375 springs.  Get the camber where the tires are happy and I wouldn't use camber to adjust balance.

 

 

Sorry I was vauge on the lowering. The ride height is 6-1/2" now as measured from next to the pinch weld front and rear. It was quite a bit higher maybe just 3/4" lower than stock.

 

 

Thanks again to everyone.