euro.r

so i gather that both bars worked in well with the car and provided neutral handling? Did the 350Z understeer/oversteer fro mthe factory? I'm curious to know if the front bar is even needed on the is350.

fritZman

This is probably a longer answer than what some want, but I figured I'd share my experience from the last few years of suspension tinkering.

FYI, if you're not used to adjustable bars think of them as elastic bands. The stiffer you go (sway bar end links are placed furthest in) the tighter the elastic band you're trying to ‘pull’. It resists more roll energy (pulling the elastic) however there's a more dramatic release when traction limits are exceeded (bigger snap when you release one end of the elastic). I found a stiffer rear bar setting on the 350Z caused more of a snap over steer when the tires did let go.

The 350Z under steered from the factory (worse than the is350 it seems). However, for large changes in balance/handling I like to use tires and springs/dampers rather than sways. So I ditched the non-stagger setup and ran 255 front and rear on the 350Z (I also played with spring rates but we’ll stick to tires and sways in this discussion). Non stagger helped my 350Z a LOT and is the primary reason why my new Azenis for the is350 are 245 up front and 255 in the rear. I’d run even wider up front but it appears as though the 245 are pushing it.

In terms of handling, I used the Hotchkis bars to help my 350Z with improvements in overall roll stability and fine tuning rather than huge changes in the balance. It's not that you can't use sway bars to make dramatic changes in handling, it's just that running super stiff settings or large variance between the front and rear has its consequences.

First, you actually begin to lose independence in your suspension with a super stiff setting. So movement on one side actually gets transmitted to the other side. Bump steer was really noticeable on the 350Z with the Hotchkis at full stiff up front.

Second, as mentioned above stiffer settings tend to have a more aggressive release when limits are exceeded.

Third, stiffer sways will increase the spring rate, so the stiffer you run, the stiffer you indirectly make your springs (makes for a harsher ride etc).

Fourth, noise from the bushings and the bar ‘walking’ (although that’s been fixed with newer Hotchkis bars) tend to increase with stiffer settings. Often the sway bar end links can be overwhelmed and start to flex or break completely.

Fifth, stiffer settings can actually cause inside tires to lift in a hard corner which is a real PITA with open and Torsen diffs…

Sixth, large variance in sway setting between the front and rear cause for inconsistent handling feel and can expose chassis flex in some cases.

So with aftermarket adjustable bars on an OEM suspension, I recommend using both the front and rear bars, and stick to full soft or medium settings only. Hotchkis does an excellent job configuring the bars to improve OEM handling traits. The rear is almost always stiffer then the front but the increase in stiffness is large enough that you need the front bar to offset some of that jump.

One more thing. Getting neutral handling by reducing rear end grip is not always the best final solution. Try to focus on increasing the front end grip instead. That way you improve the balance but also increase the cornering limits at the same time. If you don’t want to invest in wider/stickier tires up front then look into more camber or something.

ISF_GG

iTrader: (2)

Good write-up fritZman! Overall, my goal is to always try to achieve as close as possible to neutral handling when modifying any suspension. I agree that wider tires are important, especially when we only have 225's up front (on the factory 18's).

Gernby

iTrader: (1)

Wider tires in the front might help, but it isn't as much of a change as most people might think. It's important to note that wider tires don't necessarily wind up giving you larger contact patches. The air pressure is going to play the biggest role in the size of a contact patch. It is entirely possible that a 225 at 35 PSI could have more rubber touching the ground than a 255 at 37 PSI.

ISF_GG

iTrader: (2)

Agreed. Although when comparing a 225 to a 255, the 255 will offer more contact area when properly inflated. Tire pressure is important, that is a given. Of course, when wider tires are utilized, suspension short comings become much more accentuated, requiring additional suspension upgrades to take full advantage of the wider tires grip potential.

euro.r

Great write-up, thanks!

Dodge2Dub

How do you know if you are in danger of chassis flex? Personally, on my S4, I am running a 35mm front bar and 29mm rear bar (rear bar is set to full stiff) with a bilstein PSS9 suspension. The car now has neutral handling (stock, it understeers like you wouldn't believe). Should I be worried?

fritZman

Good points Gernby.

A couple of factors have to be considered if going to a wider tire for a given rim.

The tire has to meet the manufacture’s minimum rim width. In the case of the Falken Azenis, minimum rim width for a 245/40/18 tire is 8”. For the rear, 255/40/18 minimum width is 8.5”

Secondly, how much softer will the sidewalls be when ‘ballooned’ out on a narrow rim? As per you point, it really makes no sense to have a wider tire if you need to add pressure (and potentially reduce the contact patch) to keep the tire from wallowing within the rim. In the case of the Azenis, they have very strong sidewalls (which partially explain why it’s such a heavy tire). In fact, on my 350Z for Solo2 competition, I was able to run a 255 Azenis on an 8.5" wide tire with 3 psi lower pressure than a narrower Kumho MX 245 tire on the same rim.

fritZman

I don't think there's a 'danger' associated to chassis flex, it's more of a loss of performance that I was insinuating.

If the bars came as a kit, I wouldn't worry about it.

Given that you've got aftermarket springs and dampers, I'd personally consider purchasing stiffer rear springs and soften the bar. That way you'd maintain the balance but potentially improve cornering performance - especially on rough pavement.

Gernby

iTrader: (1)

I would expect that if a person left everything completely stock, and simply replaced the OEM front tire with a 245/40 of the same make and model, the car would probably handle worse regardless of tire pressures. To make that work, you would probably have to get wider front wheels, or replace the tires with tires that have significantly stonger sidewalls to allow lower pressure (as you've stated).

If I ever get out to the track again, I will be on Hoosier R6 245/35-18s all the way around.

Signal_jp

iTrader: (1)

wow, $500 for a set. they were like $250 for my 350z. what a price difference.

Dodge2Dub

I've thought about running a higher spring rating at all four corners with the dampers to match like the stasis ohlins, however, at this point I'm invested in the PSS9's and will stick with them until the next car.

BTW, the PSS9's are great so don't take my previous statement as a complaint.

fritZman

Titan Motorsports in Florida usually offers Hotchkis sways a good $200 off MSRP.

They don't have them in stock yet but by spring I'll bet you can get a set in the range of $350.

05LSV

On another Hotchkis note - did anyone notice the Sport springs' specs?

Front Drop = 1-5/8” (41mm)
Rear Drop = 7/8” (22mm)


Could be a perfect drop for the IS considering the front fender well gap size compared to the rear. I know many kits drop a tad bit more in the front than back, but this is pretty substantial.

Anyone running Hotchkis springs?

Dodge2Dub

The spring rate on the Hotchkis springs are F/350 lb and R/380 lb. What are the stock spring rates for the IS350? Also, Hotchkis states that their springs will work well with the stock shocks. Does anybody think that the stock shocks will suffer from premature wear if mated with a set of lowering springs?