jreiter

iTrader: (6)

I'm not really sure what to do about this, and some searching didn't turn up the problem. Was hoping you all could shed some light on things for me.

Basically, I've been noticing that my Z's handling seems to get quite "twitchy" sometimes. The worst situations seem to be when I'm in the process of cornering and I hit a bump of some sort (even a small one). When that happens, the car seems to want to quickly and suddenly turn quicker into the corner. Some quick searches on the web seem to suggest that this is indeed bump steer. It can be quite unnerving, especially when I'm driving hard out on twisty, 2-lane roads. It can even be difficult to keep it inside my lane on the worst occasions.

Is this common on 350Zs, or is it maybe something I've caused with my suspension mods? I have RSR Ti2000 springs, Koni shocks, and Hotchkis swaybars. I've tried a couple of different swaybar settings to no effect (didn't think that would fix it). Is it possible that lowering the car can mess up the geometry enough to cause this problem, even with a relatively conservative spring like the RSRs?

I'm willing to put the stock springs back on and give them a shot, but I'd like to make sure they would actually help before spending the money to have them reinstalled. Can anyone point me in the right direction here?

Thanks.

Q45tech

Whenever you lower a car's body via springs the steering rack lowers yet the hub stays the same, so this creates an angle across the tie rod. You must develop a method to bring the tie rod back parallel with the road. To avoid [tie rod toe angle changes] called bump steer.

350Zteve

iTrader: (6)

Have you checked your alignment since installing the parts? Lowering changes the toe angle. Setting your toe back to 0° or even a little bit of toe in would help reduce the "twitch"

abui01

iTrader: (68)

I had the same problem WITHOUT lowering the car and only having hotchkis sway bars. Perhaps the sway bars put extra tension on the endlinks causing them to bend and make this twitch happen. Then again, my friend put on his stance coilovers without swaybars and he experienced the same "twitch" when hitting a bump during cornering...

Kolia

iTrader: (2)

Stiff swaybars and mid-corner bumps don't mix well.

That's something to keep in mind also...

jreiter

iTrader: (6)

Definitely. I'm a big fan of proper alignment. It's been quite a while since I had this suspension installed (and the subsequent alignment), so I'd have to dig out the results sheet to see what the exact settings are. However, I seem to recall them all being very tight within spec. The RSR springs only lower the car about .5 to .6 inches, so there was still enough adjustability to get things back within factory spec.

jreiter

iTrader: (6)

Well sure. But when really stiff suspension hits a bump during cornering, I would guess that tends to cause a loss of traction, resulting . In my case, this thing most definitely has more grip... it tends to grab *more* and shoots more towards the direction I'm steering. I definitely think it's bump steer.

My real question is: Would the stock springs (with their slightly taller ride height) reduce or remove this bump steer? As Q45tech mentioned up above, lowering a car does alter its geometry and can certainly cause issues like this. I figured that was probably the case here. I'm just concerned that putting the stock springs on won't actually help much (as abui01 mentioned up above), and I'll still be stuck with bump steer *and* more understeer (due to the stock springs' softer rear spring rates).

FritzMan

FWIW, I found that running the front Hotchkis sway full stiff would send too much feedback into the steering wheel when hitting a bump in a corner.

Medium setting was much better. I now use stiffer springs to control the front instead.

As for lowering, I've previously run as low as 26" (ground to fender) and effect of a full stiff sway was not reproduced.

What tires are you running? Considering your mods, I would figure you've moved on from the OEM RE040. If not, I'd consider ditching them as they seem to have a really un-nerving 'jiggle' when hitting a bump in a corner.

johnlotusboy

iTrader: (1)

Tire inflation? Shock settings?

sk26dett

iTrader: (16)

bump for an update on how it turned out, i'm having the same problem right now.

Jarred@Z1

iTrader: (4)

well there is many a thing that would cause that tire size and type alignment shock and sway bar setting tire pressure ride hight type of bumps how much cornering load. Id suggest straying away from stiff anything soften the shocks and sways and see how that makes it feel. If you have the car too stiff it can feel twitchey especially without any kind of aero package. is the front or rear higher or lower than the other? I would try lower shock settings and softest sway bar setting. Ride hight only has a small amount to do with it unless its more than 1/2in front to rear. I know the nissan motorsport springs make the back of the car sit lower than the front causing all kinds of weird handeling problems. We fixed this by installing 2 very large and thick industrial washers on the perches and leveling the car out. Just my .02

sk26dett

iTrader: (16)

Well my car is bump steering pretty badly and these are my alignment specs:

Front(L/R)
Caster: 8.7, 8.5
Camber: -0.8, -0.9
Toe: 0.05, 0.05
Total Toe: 0.10

Rear(L/R)
Camber: -1.4, -1.3
Toe: 0.1, 0.1
Thrust Angle: 0.0

I'm currently on stock springs and shocks, but my hotchkis sway bars set to med front and rear (3 hole version). Changing the settings doesn't affect the bump steer either, it's always there. Any help is appreciated, I've been trying to fix it for a while now.

johnlotusboy

iTrader: (1)

What wheels with what offset are you running?

nothix

iTrader: (27)

^ what does that have to do with it?

WTX350Z

iTrader: (8)

+1 to both of those comments - bump steer is best diagnosed as bump steer when driving straight...hitting a bump. lightly hold wheel. if its bump steer the car will generally go one direction, then back the other way (on entrance and exit of the bump.) testing on a turn is going to be misleading as there are more variables.

WTX350Z

iTrader: (8)

take pic of rack and pinion unit, that includes inner/outer tie rods to the knuckles. something is up w/ your car.

ever bottomed it out really hard? I worked on a miata once that got slammed so hard it bent the subframe that held the rack, thus inducing bump steer. the subframe got pulled by a frame puller @ body shop and problem resolved. If the car has ever been wrecked this could also be the cause.

With all drivability issues I always say check air pressures on all 4 tires just to ensure there are no issues there....KISS theory.

If you were to take the car to a good suspension/alignment shop they should be able to find out the cause...this is one of those things that gets terribly difficult to diagnose over the web.

sk26dett

iTrader: (16)

Thanks for the input, my car was pretty low for a while but it's been at stock ride height for the last 8-9 months. I don't remember ever bottoming out really bad. Also the problem has gotten progressively worst in the past 1-2 months, but my alignment specs haven't changed The wheels are the oem 18" track rims. Is there anything else i should do, replace the sways with the oem ones? Dial in the rear toe closer to 0? Could it be caused by blown shocks or would that just make the wobble worst? Thanks for any help, it's really driving me crazy .

Asterix

I think what you're feeling is because the steering link is behind the ball joint. In a rear-steer car with compliance (rubber) bushings in the suspension, the loaded outside tire toes in when it hits a bump. The bushings squish, but the steering linkage doesn't. That causes momentary oversteer.

The two solutions are to move the steering rack to the front or get rid of the compliance bushings.

Asterix

Q45tech

Unfortunately the high oem caster covers up much of the oem bump steer [toe changes with suspension changes].............this is what creates much of heel toe feathering on tires----------high caster combined with toe changes.

Important to create graphs of camber and toe gain curves with +- changes in body height.

terrasmak

iTrader: (8)

What tires and what sizes are you running???