Problem when "Strutting" my stuff (Formerly known as "Shocking" discovery).

[dr-rjp]

OK...enough cornball.

First off, a little background:

I put a set of KYB AGX's on my 1998 I30. I still have 15" wheels on it (but with 215/60 x 15 tires). Keep that in mind as I tell my tale:

Overall I like the AGX's, but, they are causing havoc with my neck injury...which is why I am contemplating selling them.

HOWEVER, that is not the problem I wish to discuss here. The problem has to do with handling on wet roads.

While the AGX's have vastly improved my handling on dry roads, on wet roads, they sometimes cause my rear tires to lose traction in turns, and that causes the leading front tire to briefly skid sideways.

The tires, BTW, are nearly new, Fuzion HR-i, and they have been simply fantastic in wet weather. Well, they were when I still had the stock struts & shocks. Then, I switched over to the AGX's.

Without knowing all the details as to why wet handling has changed, I tend to feel that the stock 15" tires are a part of the skidding problem because of how the handling dynamics have changed.

When my car had the stock struts & shocks, it would lean (a lot) into turns, but that lean could actually be beneficial in a way if that extra weight kept both the front and rear tires firmly planted to the asphalt. Of course, the extra weight on one side increases momentum and centrifugal force on that side and the tendency for the FWD car to plow into the turn is increased.

Now, with the AGX's, although the body lean is greatly minimized because of their stiffness, the car now seems to tilt as a whole to where the rear tires lose some traction on left-hand turns.

I do not know what is actually taking place, so forgive me if I tell you what it feels like:

It feels as if the car is being lifted up...as if the centrifugal force is pulling up on the car because the centripital force is pulling down on the car -- there is about 180lbs of driver sitting on the left side of the car and adding to that downward force.

If someone were to take a photo of my car from behind, I'd bet I see one of my rear tires up in the air.

OK, my question is "How do I counteract that effect?" (besides going on a diet or having a fat friend sit in the passenger seat).

Would a rear sway bar help?

Would larger diameter tires help?

Would slowing down help? (of course, it would, but me? Slow down?)

Thanks for your help.

[elwesso]

The stock springs/shocks were designed for the stock tires and their respective sidewall stiffness.. You will see a great increase in handing by getting a tire with a stiffer sidewall, at the cost of a slightly harsher ride.... Get some 17s, it will make a big difference.

[maxnix]

Fuzion is second line of Bridgestone. If they are hard (wear >220), or "all season", they will not work as well in the wet or dry above 45° F as a summer maximum performance tire. Might even upset the ABS software.

Compounding your problems is the configuration of your car with FWD and beam axle in back. Take is easy and get the stickiest tires you can run. They are the only thing that touches the road till you roll over. Don't skimp.

[Q45tech]

Body lean has little to do with weight transfer it is only an indicator to the driver of what's happening - weight transfer.

Weight transfer is purely a function of CG/tire track width x G x sprung weight.

Tire sidewall stiffness varies between 1000 to 1500 pounds per inch and is set with inflation pressure primarily.........modern tires [except run flats] have almost zero uninflated stiffness.

Measure stiffness by noting the exact loaded compression with and without body weight on tire..........how much the tire squishes down from round.............1/2-1" per 1000 pounds.

Tire spinginess is in series with vehicle coil spring and thus reduces the value of the coil spring [~~10%]........backwards from what many would assume.

Most [except ultra performance] aftermarket tires are much harder than oem tires

[dr-rjp]

Body lean has little to do with weight transfer it is only an indicator to the driver of what's happening - weight transfer.

Weight transfer is purely a function of CG/tire track width x G x sprung weight.

Tire sidewall stiffness varies between 1000 to 1500 pounds per inch and is set with inflation pressure primarily.........modern tires [except run flats] have almost zero uninflated stiffness.

Measure stiffness by noting the exact loaded compression with and without body weight on tire..........how much the tire squishes down from round.............1/2-1" per 1000 pounds.

Tire spinginess is in series with vehicle coil spring and thus reduces the value of the coil spring [~~10%]........backwards from what many would assume.

Most [except ultra performance] aftermarket tires are much harder than oem tires

OK...now how do I translate all that into applicable changes I can make?

One suggested moving up to 17" tires...which, incidentally I plan on doing down the road when I have the cash.

Another suggested buying the stickiest tire I can find. Sometimes, "sticky" means "soft" and soft tires do not last very long. The stickiest tires I have ever owned were Dunlops..but they were also worn bald by 25K.

I would still like to get a "Yea" or "Nay" on the idea of buying a rear sway bar its own merits. I've heard that it will improve handling, but are there any negatives for me given my present setup?

Other than sticky, 17" tires, any other suggestions?

[maxnix]

Another suggested buying the stickiest tire I can find. Sometimes, "sticky" means "soft" and soft tires do not last very long. The stickiest tires I have ever owned were Dunlops..but they were also worn bald by 25K.

I would still like to get a "Yea" or "Nay" on the idea of buying a rear sway bar its own merits. I've heard that it will improve handling, but are there any negatives for me given my present setup?

Performance tires are softer than billiard balls and won't last much past 20K, even with frequent rotation and flipping. Worn rubber components in the suspension will accellerate the rate of wear.

An I30 is FWD with most (60%) of its weight on the steering and driving wheels. The axle out back is not independently sprung and is a beam axle. So my opinion is you will not derive very much discernible benefit from an antisway bar. I would save for tires and wheels and suspension rubber, especially when you replace your shocks. If they are at all worn, they will not control the rear end well at all and could be contributing to your rear end stability problem. If the shocks are in specification, the rear end should follow the front pretty much like a Conestoga wagon's rear axle.

[dr-rjp]

Thanks, Brian. That is exactly what I wanted to hear. I'll follow your advice.

[maxnix]

One other thing I would do is check through the suspension parts list for the standard and touring (later called Sport (?) on the I35) parts lists and note if the shocks and springs part numbers vary between different models for the same year.

If a rear sway bar pops up on the t or s model, then you may want to get one from a junk yard and new rubber from Joe and mount it. I would be curious if there was one available. I know the Nissan engineers know more than I do.

Part of my thought is that since the beam rear axle doesn't permit side to side independent camber changes, an antisway bar would be of minimal benefit. But I am not conversant with that type of suspension. A lot of mini vans and previous generation VW used it also.

Let us know.