Does the Z have a rear toe-steer problem?
 

Those of you who have tracked the Z might be able to fill me in on this question.

When cornering briskly (a 70 mph interchange sweeper) if I hit a bump the front stays planted but the rear steps out aggressively when it gets light at the top of the bump. My other cars (04 T-Bird and 11 Volvo XC60, both IRS) take the corner with much less drama. Is this a toe steer or dampening issue or perhaps something else? Your thoughts would be appreciated.

I've complained about the same thing. I'm curious as to what the other guys will say about this.

The rear toes out as the suspension compresses. To minimize this butt wiggling feel you would want to dial in more toe-in and if you can, stiffen up your rear damper setting.

Btw this phenomenon is called bump steer.

I'm hoping to get some good feedback. It could be toe steer or possibly a damper issue.

This reminds me of a problem Suzuki had with the first generation, long travel suspension, RM 250 MX bike. The rear suspension just didn't behave well on big bumps. Turned out the rebound dampening was excessive and the rear wheel spent too much time in the air before returning to the ground after each bump. A wheel in the air can't generate cornering force. I keep thinking that our situation is something like the Suzuki's problem.

You don't value my post?

Is this condition improved with a change of dampers or switching to coil overs?

I appreciate your response a great deal, I just didn't see it because I was responding to the first responder when your response was posted.

Does anyone offer a bump steer kit to correct this condition?

He said he wanted good feedback :p

Just kidding!

I don't think it is bump steer (although you can get some), I think it is mostly the rear bouncing over harsh bumps as the suspension isn't as compliant as average car due to it's sporty setup.

Not sure of an ideal solution, you can make the suspension softer but then you ruin the sportiness for the smoother corners. Stiff rear sway bar can also make it worse.

Thanks for the link, do the actually do what they say they will do?

I really don't know, but the description fits the problem IMO.

I hear you. I'm hoping that someone has successfully addressed this issue so that we can learn from their experience.

The Megan toe links might be the ticket, maybe someone here has first hand experience with them.

I'm thinking that a good double-adjustable rear shock might be able to moderate the condition, any thoughts?

I'm hoping to avoid just throwing money at the problem.

Most of the dynamic comes from the high wheel rate out back, as well as the dynamic change in rear toe mid-corner (both of which have been jacked up vs the 350)

Nissan basically improved full-on-throttle corner dynamics at the expense of off- and partial-throttle dynamic. The 350 had a tendency to step out under throttle due to insufficient toe in the rear. For the 370z, Nissan dialed in a suspension setup that would increase rear toe more significantly during cornering, and you wind up with a bit of a "floaty" or unstable feel from the excessive toe-in. You couple this with the high wheel rate, and you get exactly what you are talking about.

I have adjustable traction arms, I don't think they really help in this situation (you already have them they just aren't adjustable).

Adjustable shocks tuned for stock spring rates are probably the best option, soften the settings for daily driving and then turn them up for weekend canyon carving.

What you are describing is toe-in when the rear suspension is in a compressed condition and a toe-out in a rebound condition, am I correct?

In your case did you change the torque arm length or did you set it at the stock length? The implication of the Megan product description is that by adjusting the torque arm length the toe characteristics can be altered-your experience suggests otherwise. Comments?

It is more track oriented than street (mine is from SPL). First they eliminate the rubber bushing to get rid of random flex, and second you can use it to alter the bump steer slightly. But like I said before I'm not sure that the suspension is compressing enough to actually induce bump steer in your case, but rather the back end is bouncing off the bumps as a result of the spring rate, or to be more accurate wheel rate as Red pointed out.

ha! :D

softening the rear damp rate will not help, actually will make it worse.
swaybars will not help in this case either.

it's completely related to the amount of stroke, toe-in angle on the rear, and damp rate. ive already experimented with this on my G35C and it's got a similar suspension geometry. it's a programmed design of this kind of suspension. i already mentioned on my earlier post on how to reduce this feel. :) this is another reason why im not running lowering springs on stock dampers.

So your thinking shocks are the first option?

Somewhat off topic (maybe) but I notice that those forum members that install coil overs always seem to comment that the ride has improved. This seems counter intuitive considering that most of these applications involve a 1.5" to 2" drop which, in my experience, usually makes the ride choppy and harsh. Now back on topic. Are our shocks known to be a problem? Is improved ride with coil overs the result of better shocks (I'm not interested in a sloppy ride) or is something else going on here and can any of this in any way be used address my concerns about bump steer?

the shortened torque arm and adjusted angle on the 370z changes things a bit vs the g35. The change results in the car generating additional toe-in under corner load, and if you take dynamic toe measurements, you will generally notice that the 370z is prone to over-toe, whereas the g35/350 struggle with stability due to no toe gain. It is a big part of the reason the 350 was unpredictable on corner exit.

if that was true, dont you think i would've jumped on c/o's 2 yrs ago? :D

the reason why my car has stock springs and dampers is to maintain balance and stoke for street. the car can use stiffer dampers so this is why ive been thinking about running koni's and using stock springs. lower ride does not = better handling. actually it worsens it on street as it's not a controlled surface like on the track.

the principle is the same. the rear toes-out as the suspension compresses. that's why the wiggling butt. the 370Z is much improved vs the G35C, but as i mentioned, the design shares the same principle.

Is more toe going to eat the rear tires, or do you just bias it to the factory maximum spec for toe in? Whose dampers do you like?

more toe-in condition (0.40 total) will eat at your tires, but it will improve straight line stability for sure. but stiffer dampers will net your a lot more on this type of suspension.

on stock springs i think im going to be okay with koni yellows which are only re-bound adjustable (yellows are usually only re-bound adjustable and i am assuming the same for the 370Z's set). unfortunately this is the only damper set currently available for the 370Z that i know of. my only other alternative would be to get coilovers with near stock spring rate, linear rate springs, and keep stock ride height, use the adjustable damp settings to tighten up a little bit.

if im running progressive rate lowering springs i would prefer to have simultaneous adjustment dampers for street (bound and rebound stiffens together like my tokico D-Specs on the G...but not available for the 370Z). my goal would be to minimize suspension movement since it's already sitting near the outer stroke range of the stock suspension from the lowering springs... sacrifice would be some ride comfort. tires are eating pretty quick but i was able to get ~10K with sprited driving on RE050A PolePositions so that's not bad at all (currently running the new S04 PolePositions :p ).

Kenchan, Red_Zed, I'm learning a lot here but if I'm reading your posts correctly kenchan says it toes out under compression and Red_Zed says it toes in under compression. Pick one.

My butt-o-meter suggests that the rear suspension gains significant toe in as it compresses because the car smartly (more like abruptly) steps back in line as the suspension compresses as it lands on the far side off the bump. If the toe change is radical enough that it goes to a near zero toe or (worse) a toe out condition at full droop when it launches off the bump and then gains a lot of toe in on compression we might be onto something as such a behavior would cause the condition I seem to be concerned about.

Comments?

except the shortened torque arm creates toe-in on compression. the funky wandering feeling described here (and in many other threads) comes from excessive toe-in.


I can't speak for the G35 for sure, but when I did bump steer measurements on my 370, I started at ~1/16*, and went to ~3/32* at full compression on the rear.


You can hook your Z up to a bump steer gauge if you don't believe me.

Regardless of toe in or toe out, firmer shocks would reduce suspension travel and minimize undesirable toe changes,

Would an adjustable torque arm allow you to tune out some of that toe change?

Red_Zed, am I reading that right a total increase of 1/16" additional toe in? Is that from full droop to full compression?

I bought better tires, redid the alignment and the problem went away. My car felt nervous as I drove home from the dealership too

Don't keep me in suspense, what tires, what alignment specs?

Firmer suspension will reduce the bump steer but will increase the bounce on very sharp bumps. How many miles on your tires? Might be time for a good alignment.

Yes, and yes. The change from full droop to body weight compressed is relatively minor, too, so most of the toe is getting dialed in on compression from rest.

I don't know wat happened on your car, but on mine the stock rear toe-in appears pretty aggressive as it is. 4K on the stock tires and 1/2 worn. I'd want more toe-in?

Redzed- I will need to check into wat you posted.

5K on the the original tires, the wear pattern is near perfect, no irregular wear.

A little context please: I've done a lot of reading on suspension design over the years and I know that bump steer is generally to be avoided. Since bump steer characteristics, on a production car, are rarely adjustable I have no practical experience altering them, so please help me out, is a 1/16" toe change (most of it on bump) considered to be a lot/excessive for a car such as the Z?

When contemplating the Megan Torque Arm as a possible solution:

1. Changing the inner pivot point (dropping it or moving it in a bit, probably not practical) could alter the bump steer profile.

2. Changing it's length (most likely longer) would reduce the angularity of the torque arm over it's length of travel which should "soften" or reduce the total amount of toe change. This assumes that there is enough adjustability in the torque arm to make a meaningful increase in length and enough adjustability in the rear suspension to bring the static toe and camber adjustments back into spec.

Comments?

I honestly don't remember off the top of my head. Alignment on new cars can be spotty given the abuse some of them had. I traded in a stock RX-8 that had Direzza Star Specs and a relatively tame alignment on it. The car handle corners with grace and had no drama. On the way back from the dealership, the Z felt nervous at the same exact speed on the stock RE050a. I immediately went out and bought myself a set of RE11 along with an alignment. I basically put together to 1/16 toe in in the front, about 2 degrees of camber in the back along with I believe about 1/8 in toe in in the back. The nervousness I had with the car was gone right after. Heck, it took me a good two years before I had anything close to a spin.

Interesting. Mine has been rock solid in all modes from the day I got it except for this one issue. That's the reason for my initial post, the apparent bump steer issue stands out because every thing else is so good.

I am choosing my words carefully here to avoid having them misconstrued by some of the overly sensitive members here, so the answer I will give is I believe so
I would agree with both of these. I also agree that the first is likely not practical.
I have no real experiece with the Megan arms, but I am always hesitant to use Megan parts. I know that a longer arm is needed to get good bump dynamic, but at the same time, I don't imagine you have the time/money to play around with a bunch of different parts.

If you do get the Megan arms, definitely post up thoughts though. I'd be curious to see if it sorts out the craziness (and it would be pretty helpful for anyone else that experiences it)