Hey guys,

I’ve had my Z for just under a month and I’m still learning about the dynamics of the vehicle. I have yet to hit the track, shooting for the next Auto-X event in March but through some aggressive back road driving I have identified some areas of concern.
One that has me puzzled is on a moderate speed corner, say 4k in second, any slight irregularity/bump in the street will throw the rear off, creating a slight rear end skip leading to a touch of over steer and forcing me to lift off slightly and apply steering correction. My question is how do I best tackle this? The vehicle is a base 05 so no LSD w/31k miles by two previous owners and it “appears” the shock/struts have some good life left in them. Would an aftermarket shock swap cure this or do you think the stock 17”’s need upgrading. Any advice would be most appreciative.
Thanks,

Neil

 

If you have the stock suspension and tires it could be a natural situation. By lifting off the throttle abruptly mid corner, you are upsetting the balance of the car and transferring weight to the front of the vehicle. This transfer lightens the rear by lifting it and thus lower the level of grip available in the rear. Now if this is not the case its likely you have a mechanical issue.

 

omg stop driving your car now, there is a serious problem.

 

What you're describing is not the usual dynamic handling trait of a stock 350Z. Nissan designed in a lot of understeer and you're more likely to find that's the limiting factor at an autocross. I'd also check the condition of your rear tires if your Z continues to be loose. Z's can go through rear tires quickly, if driven aggressively and that might be your problem.

 

earlier Z's (pre 2004.5) had different shocks than newer Z's. I believe switching out your shock swill improve that handling. Koni's are good replacements for the stock pieces.

 

The OEM open diff isn't helping matters but it's hard to give you a full review without being in the car. Are the bumps that severe that you absolutely can't continue adding some more throttle?

Has camber, toe, tires, and shocks been checked? Sway bars?

If the car is bone stock, it really shouldnt be behaving as you described unless something is amiss.

 

I think your right and its more driver error rather than the car. My guess is that the bump is abrupt enough to upset my footing on the accelerator forcing me to lift. I'll try the corner again and if I end up in the Armco I’ll just blame Motormouth.

 

It’s a single bump running the width of the lane; mostly likely a patched-up strip of black top. I just had an alignment done by Prescient Z to factory specs, as the vehicle is bone stock, so all looks good there. I know it’s rather hard to determine without being in the car from what I'm reading it appears to be more of a case of driver error.

 

haha!

There was a bump on a road in NJ that used to mess up my braking. it was as you described, a lane-wide fairly serious buckle in the asphalt and while braking into it (it was a left hand yield to merge lane) the ABS would always shudder a bit, and if I had the lane, accelerating through it would make the rear end jiggle around.

You might just be oversensitive to the movements of the car, since it is new.

But to answer your question: no, it is not normal for a Z to lose rear end stability over a moderate bump in the road, while cruising. I can not imagine anything less than a real issue with your suspension causing this. As others have said, when you have a moment, go over the rear suspension bolts and bushing and make sure everything is still there. I doubt there is an issue though.

 

i have discussed with other local owners a similar feeling. i am lowered on gf210's with SPC rear camber arms and tow bolts. on the stock 17" wheels and tires it isn't as aparent as on my 19" RE30's. while cruising it feels as though the rear tires will grab the imperfections in the road and try to drift away from the car. at first i thought of alignment so i got it checked, still felt it so went back and got it rechecked. talked to a local shop that said it could be the SPC arms, so swapped to stock got it aligned(again) and still felt it. thought it might just be because of running a 285/35/19(first a pair of goodyear f1 supercar, then michelin PS2's) in the rear, but other local member running the same sizes say the feel the same thing(even a local G35 stock on stock 19's). now in the process of replacing the diff bushing and going to try SPL rear arms. i understand mine is an 04 with about 70k on it, but i would expect a "sports car" to have a better feel to it

 

It's been years since my 05 base was stock.

I don't remember having the problem you are describing, but I try to avoid hitting large bumps when the car is near the edge of traction. (I try to settle the car as best I can before hitting such things, if I can't avoid them altogether.)

There was (is) one "suprise" bump in a very bad spot on hwy28 near Fontana Village at ZdayZ. It did unsettle my Z when in stock form, but I think it upset most cars.

 

The stock sized tires have understeer built-in. If you change the tire widths, then you do change the balance of the car, sometimes significantly more than the tire width difference might suggest.

The other thing is that large bumps in the middle of the corner have a significantly larger effect on a stiffly-sprung car like the 350Z than they would have on something a bit softer.

 

I suggest you stop stuffing things up there if your rear is becoming loose

 

Well said.

Tires. Some tires are skittish (best word I can think of). Uneven pavement or concrete expansion joints they seen to be "searching" for a flat spot to regain lost traction. Natural tendency is to back off the throttle. Of course doing so reduces rear tire torque which may exaggerate the condition.

 

 

what kind psi are you running in the rear tires?........also is it getting loose in any other turns or is it just that one?...........because you could be miss diagnosing a push............alot of people think that a car is loose just because the rear-end is coming around but most of the time it ends up being a bad result of a push. Alot of times when making the first cut into a turn and trying to get a tight car to pivot down to the apex of the corner most drivers will try to steer the car down to the apex and jack the mess out of the steering wheel and by the time the rear tires break loose (via weight transfer, bump or whatever) the steering wheel is still jacked and the rear comes around on them.............however if its a true loose situation then i would just make a air psi adjustment to start with because if you start with big changes you'll be out in left field all alone before you know it!!!!

 

I'm sorry, I lol'd at the title, is that immature?

 

+1
You beat me to it!
I think he went to one serious prison, and was pimped the ffffuuuuuuuuukkk out.

but I mean if you're a female, then no problem... Just sucks that you have a loose rear end. Does that mean diarrhea just falls out like a water fall?

 

Did either of the alignment checks come with a printout? I'd like to see what they are saying is OK. I had two separate shops try to pass off a toe and camber setting that was way off as OK. After trying to play with the alignment myself I found the trouble the two shops had...with the SPC or similar arm, you wouldn't expect toe to change along with the camber but it does, and by a significant amount. So when you get one right the other needs adjustment. The two shops I went to didn't notice the separate toe bolt cam adjustment and only used the SPC rod for both, compromising the setup. The car uses a near zero toe-in and aggressive camber setting, and if the toe is off the car will handle erratically at the rear especially in the wet, or on large dry rain grooves in the road. If this isn't it, I would continue checking for broken or loose connections in the suspension as you are.

 

Since you purchased the car used with 31k miles, there are a few things you should look into first:

1. Check the condition of tires. Very low or very high tire pressures have very little grip. Also, if the front tires are newer, and the rear tires are old and hard, that will cause the rear to kick out suddenly.

2. Check alignment settings.

3. Check shocks. At 31k miles, they should be fine if they are OEM. Check to see if the springs are OEM. Some aftermarket springs are too stiff, and simply do not work with OEM shocks.

4. Check bearings for play and all the links/connections. Lift the vehicle and try to wiggle the wheel in search for looseness. Take a socket set to all connections and test bolt tightness (do not tighten more, just check to make sure none are loose)

5. Maybe that bump is simply rough/big enough to knock most cars off their intended path. Are you sure you don't get any understeer before oversteer? The bump could knock the front end out first, then the rear end, but you only notice the rear end give away.