Chassis Help! Need a track day set-up.

SG4247

I am new to the road course deal, and have my Z in the shop now prepping for track days in April.

This car is a 2010 touring model, with rear adjustable camber arms and toe bolts. Stock suspension components otherwise.

I just installed new RE-11 285/35/19 F on 19x10, and 325/30/19 R on 19x10.5 wheels, and did a four wheel alignment.

Car works pretty good, except that when I go through a long sweeping 45 degree turns at high speed (VDC off), the car begins to wiggle. At first I thought it was porpoising, but after several attempts on the same corner turning both left and right, the car has a significant wiggle coming from the rear.

This happens under full power, part throttle and coast at a certain speed. For example, it is stable through the corner at 80 mph holding part throttle, but when I increase the power say mid-way thru the turn, to increase speed to 85 mph, to blast out of the turn exit, the wiggle comes on and continues even though the tires do not feel like they are sliding or spinning, the car is still under my control, even if just barely.

If I suddenly brake during the corner when the car begins to wiggle, the outside front tire will lock up, and chatter due to the ABS.

Very strange behavior to me, is this car pushing? Is the different tire widths causing this?

Not sure how fix this problem, but I dont like it.

Any help would be greatly appreciated.

Boss_302

Start with throwing away the factory shocks, and go with a good performance set, S-tune NISMO, Bilstines, Konis, and a good alignment, the car will feel so much better.

SG4247

Thanks 302, I hadnt even considered the shocks.

The car seems to have a lot of body roll with the big RE-11 tires, so I was thinking it needed better sway bars, especially in the front.

Still dont understand why it has the wiggle issue.

Would the body roll conbined with my camber setting of -1.0 degrees (all four wheels) cause this?

BGTV8

So you have the VDC off but there are still nannies in operation

How hard are you pushing the car (is you experience level as a beginner, or some experieence in pushing a car).

My reason is that the residual stability control might be detecting sufficient yaw for it to trigger one rear brake to try and straighten you up (not ideal on a road course).

Check these threads
DIY Yaw Sensor rocker switch and
How to turn off vdc completely
Look at the bottom of page 2 of first post for explanation of trail braking - you will experience a similar feeling if you are close to the lateral grip or traction limit and the car senses wheelspin

Solution - install a switch in the power lead to the yaw sensor.

SG4247

I am very experienced in fast cars.

So, yes I can push it right into the barrier!

I had considered the yaw sensor interfering and have seen it come on at low speed when doing 180 type maneuvers.

I didnt notice the yaw sensor light blinking during this test, but at that speed I could have missed it, but it also doesn't mean there aren't electrical shinagans going on without the light.

Any other thoughts?

ufoz8mycow

Sounds like your yaw sensor is kicking in a little active handling. The link above will solve your issue. Beyond that there is no reason your car should be wiggling around unless we are talking unbalanced wheels, warped rotors, etc.

SG4247

I just turned all four factory rotors, and installed XM72 pads.

Brakes are excellent - and no chatter or vibration felt so far in the pedal.

The wheel balance feels pretty good also. Wheels and tires are both new.

In a straight line, the car feels great its hands off even way over 100 mph, but in fast corners, it wants to like crab walk.

Is the excessive body roll causing my low -1.0 degree camber angle to reduce the tire contact patch on the front and rear inboard tires?

BGTV8

1.0 deg neg at the rear is about right.

If the car feedback is abrupt and giving you a "holy cr4p" moment, then I would put a switch in the car to isolate yaw sensor as first step - takes an hour or so if you have crimper,s some wire and a switch.

If the car feedback is the same with yaw sensor disabled, then I would suspect rear wheel bearing, or rear-steer as a consequence of rear suspension bushing that are FUBAR. You can check wheel bearing by seeing if there is any free play with a wheel unloaded (in the air).

A pry-bar on suspension rods will give you an idea on bushes.

I am assuming that the crab-walk is coming from the rear per your original post.

Other alternatives to look at are rear tyre falling over (what pressures are you running - this can only really happen if pressures are really low - like 20psi)

The other thing is that the tyres are too wide for the rims - especvially at the rear ..

According to my version (Australian) of Tyre and Rim Assoc book, 325 width needs an 11" wheel minimum and 12" max. I would not have thought that 10.5 was too narrow, BUT this may be pressure sensitive, especially if you are really loading the suspension when the car initially takes its set.

If the car is not porpoising, then I cannot see the dampers being the issue.

Park your ars3 on the rear quarter and give the car some weight and step away ... if the car does not settle in 1 or 2 (max) oscillations, that would indicate a damper that is shot, but since you say it is the same in left and right turns, it would be strange to have both go out at the same time ....

I do keep coming back to the residual electronic nannies - Nissan have set the OEM threshold very low, so simplest check is to switch the yaw sensor power, which you will need to do anyway.

Good luck

Over_ReV

I had this same issue, where the rear would feel like it's wiggling to the side going around a corner even when the tires were not losing traction. I thought something had to be loose in the suspension so I jacked it up and found everything tight. I found a thread on here with someone else having the same issue and they solved by using stiffer rear shocks. Sure enough I stiffened mine and the issue 100% went away.

It also sounds like you may be having VDC intrusion, and if you are capable of driving the car close to the limit you should definitely do the yaw sensor switch mod.

Good luck hope this helps!

SG4247

Thanks guys really appreciate the help!

The car really does feel like something is loose in the rear suspension, but nothing unusual has been found.

This gives me some direction to go forward with.

Thanks

Boss_302

A good set dampers will make a difference in the handling. The factory shocks only go so far. I have 40K on my 2011, after installing a set of performance shocks the car feel so much better and more confidante in the turns. One thing I should have added was to go thur and check the rubber bushings on the suspension pick-up points, That they are in-tacked and in good shape. Any looseness will cause movement in the suspension which will effect alignment and the car will do all kinds of funny things.

SG4247

The rear tire is pretty wide for the wheel. This means the pressure is critical to maintain the desired tire cross section. Right now I have the rear at 34 psi to keep the center of the tire level with the tread corners. This may be alittle high...

What shocks would be suitable for track use and are affordable?

Looking for rear shocks right now, and the yellow Konis appear to be the best value at $228 each from flea-bay. Cant afford Blistein or S-tune kit. Nismo shocks are doable, but konis seem like a better deal since they are adjustable.

302 - I will look all the rear suspension points over again. I may even go back to the alignment rack and make sure the rear toe in is not off.

m13s

Agree what everyone said on the YAW sensor. I am new to the platform but physics are physics.

I would think about going to 18" square setup to start, add stiffer springs front and rear with a good set of coil overs. Talk to your tire and suspension guys to see what they recommend for the type of driving that you do at the track. Pressures are key along with camber.

Depending on budget you will have to make a determination as to what you feel works for your wallet.

For my track set up we run 18x10.5 squared, 3.5 - front and - 2 in the rear. 2 way adjustable JRZ and I'll have to check the spring rates. We do NOT have any nannies on the car including ABS.

Rusty

1. How many trackdays you have done?
2. Stock sway bars?
3. What are your alignment specs? Post please.
4. What are your rim spec?
5. What are your tire specs?
6. What is your tire pressure front and rear?
7. What other mods have you done to the car?

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Boss_302

For nismo shocks take a look on e-bay, there are some salvage yards that have had some new 15/16 Nismo parts for sale. A lot of the stuff is low mileages and like new. I missed a good set of Nismo springs and shock at a good price that where like new. They're the same as the s-tune. Believe me I did my homework. I also picked up a bunch the Nismo braces at a fraction of the cost that they are being sold new.