so on my 5.5 gen, i'll be ordering the 23mm fsb poly, correct? i saw two different sizes on a site and wasn't sure which one was the size i needed without measuring.

 

Norm. I already had the RSB on when I put the front bar on. If the rear was unloading as you say, it was unloading way less now with the front bar on.

I ran the car in vaious situations w/ the front bar being the only change. I couldn't feel any more understeer. But I did feel the car exhibiting alot less dive in with the turn of the steering wheel.

Matt Blehm actually took his stock bar OFF for track events, thinking it would help. Now he's either found or is actively looking for a ST front bar for his 3-gen. He was also using some very stiff custom front springs at the time.

All I have to say, drive a maxima with a front bar and decide for yourself. If the oem bar is hollow like the 3-gen, then it would be easy to build a stiffer one that's solid and have all the stock dimensions.

Maybe it's because the VE30DE is on heavy **** of a motor. Or maybe it's because the 3-gen has an IRS suspension. I don't know. All I know is the front bar was a great mod for my car.

I don't quite understand the fact that you don't want people to use a stiffer front bar but you do advocate the use of stiffer front springs(in the front). Both would increase front roll stiffness and increase understeer in your theory

 

Cornering hard has the bar working against the inside wheel's spring, meaning that the inside wheel has a tougher time maintaining contact with the road (read: less average grip). I'm mostly looking at sta-bars as a means of fine tuning, and another tool for working the compromise between ride and handling, but keep in mind that I'm philosophically much more in line with the performance side of this issue and have a preference for a firm-ish ride anyway.

In one softcover book or another, mention was made of a general range of relative stiffnesses between bar and springs, with the bar effect suggested to fall between 50% of the spring effect and equal to it (this for a performance application). Keep in mind that the suspension's independence decreases as this percentage grows. The "sweet spot" is fairly wide, though the further away from optimum you go the more you give up.

I haven't measured up the Maxima's front bar and its attachment locations on the control arm and chassis to determine its rate and motion ratio, but suffice it to say that the MR (squared, for proper comparison with the springs for wheel rate purposes) is substantially less than that of the spring (which is only slightly less than 1.00 for most MacStruts). But if the Max's geometry is at all similar to the front suspension of my 626 (save for the control arm attachment location, which I know is different), a 22mm bar is worth about 100 lb/in of wheel rate, and a 23mm bar only ups that to 125 lb/in. I doubt that you'd notice another 25 lb/in of spring rate out of 150 or so (~15% increase?) much more than the 1mm bar size increase.

Stiffening a sta-bar's endlink and chassis bushings - if thoughtfully done - mostly makes the bar more linear. The ultimate roll angle doesn't drop much, because the OE rubber compresses as it is loaded and gains quite a bit of rate in the process. But having the first half degree of roll add the same amount of bar loading as does the last half degree makes for more predictable behavior. Theoretically, this should also add harshness, but I don't think I've ever heard anybody complain about this mod (or when reducing compliance in the sta-bar linkage is done as OE).

Norm

 

If the maxima stock bar is hollow, then one could make a solid bar that's X% stiffer w/o increasing the diameter. Or one could make it solid and increase the diameter 1-2 mm for even more stiffness. And aftermarket front bars for teh 3-gen, come with Energy poly bushings

 

Would you go for a 10 dollar one thats round or a 40 dollar one thats thicker and more rigid lol

 

Maybe, maybe not. When you adjust Illuminas you change both the bump and rebound response curves (by different amounts). You'd need to know what the OE and the five different Illumina bump curves look like. What I was getting at is that you need to change the ratio between bump and rebound damping. It's a "slope of the curve" kind of thing on certain shock plots.

I'll try to work up a simplified and fictitious example (so please don't use any of the following numbers for anything but theoretical discussion).

Let's say that with your OE springs that your OE shocks provide 20 lbs of bump (compression) damping at a certain piston velocity and 40 lbs of rebound damping at the same velocity. Everything is fine. You might think of this as a 33/67 shock.

Now put springs in that are twice as stiff as OE. You want less bump damping than 20 lbs at that same piston velocity, perhaps 15 lbs. But quite a bit more rebound - more like double, so let's say you now want 75 lbs just to make the math easy (the valving now is 20/80).

To some extent, Illuminas achieve this "widening" of the difference between bump and rebound damping. But I think the bump curves rather than dropping with increased settings just don't increase very fast. They MAY do something like 20, 21, 22, 24, 26 in bump and 40, 45, 50, 60, 70 in rebound (and let me emphasize that these numbers are also arbitrary guesses). So the various settings vary between perhaps 33/67 and 27/73, which may be OK, if the absolute values of the bump damping aren't very high to begin with or if the 20 is already a relatively low number. Some Konis, for example, have considerably greater bump damping (perhaps 30 or 35 on the above scale, combined with ~70 rebound), and some folks have had success by reducing it via revalving.

What you're trying to avoid ride comfort-wise is having the total of the change in spring load due to its movement plus the shock loads in bump (spring and shock compression) change much. Load added through the spring is a function of how far it has moved, while load through the shock is a function of how fast it moves and its damping curve. Somewhere between zero movement and maximum movement the maximum combined load of

[spring rate]*[displacement] + [damping factor]*[velocity]

occurs, and that's what you're trying to limit.

The rebound side doesn't have nearly the same impact on ride, as the spring and damping terms oppose each other, with the chassis seeing the difference between them rather than their sum. Never mind that with much rebound damping at all the spring cannot generate velocities in extension that are anywhere near as high as what you get from hitting a bump.

Norm

 

i got a SPW bar for around $30 or 40. from what iv' seen this design is similar to more expensive "name brand' bars. i think this price includes shipping. i only remember its an SPW bar. if you take a cross cut, it looks like a H. i imagine the super cheapo bars will not work as well as the thicker ones. for the extra $20, i would get the more expensive one.

 

Thanks for all the info norm!

 

A little off topic, but won't low bump dumping combined with high rebound dumping cause the vehicle to eventually bottom out? As far as I understand, it will be very easy for suspension to compress but it will take a long time for it to recover, so the car will be getting lower and lower. I know that that's the way most shocks are valved but I don't really understand why and how they manage to avoid this slow decrease in ride height.

 

Yes, it is entirely possible to overdo a good thing and end up adversely affecting ride height. 90/10 front drag shocks are a classic example where this sort of shock behavior is actually put to good use.

At this stage, you really need to work with actual velocities and damping forces rather than just relative force percentages. While essentially dead shocks with damping forces of 1 lb in bump and 2 or 3 lb in rebound might sound OK from a relative percentages point of view, in an actual installation they would hardly be any better than no shocks at all.

The damping forces from the shock have to be in some relation to the spring rate, though there is a fair bit of tolerance either way. The amount of damping for best road handling is two or three times that for best ride comfort (see Section 22 in RCVD). "Percent of critical damping" is a dimensionless way of expressing the amounts of bump and rebound damping to the relative times it takes for the bump and rebound portions to be completed. In the mathematical derivation for damped vibration the amount of damping present does affect frequency (IOW, bump and rebound times).

Then it starts to get complicated. There is no requirement whatsoever that a shock retain the same percentages or even percentages of critical damping for all piston velocities. Most shocks don't.

Norm

 

I think you guys have missed a big reason why they arent made. If you look at the cars with aftermarket FSB, they mount from under the car. Ours is a huge PITA to get to since its mounted on top of the sub frame. I know its not the only or main reason, but it has to have some affect. No one wants to get into a job that big.

 

Nope. That's what I was referring to back on the first page of this topic. Replacing the front sta-bar on the Mazda 626/MX-6/Probe chassis involves the same disassembly, as I suspect do most FWD cars. There just aren't that many different ways to package all those bits into generally similar spaces.

In the end, the ground clearance issue with the simpler "underneath" installation is apt to be a deal-breaker, such as for severely lowered vehicles or truly horrid pavement conditions. BTDT a bit over 30 years ago (and let's just say that the pavement makes for a pretty effective grinding wheel on such components as chassis brackets - fortunately 1/8" steel strip was cheap and readily available).

Suffice it to say that the above durability issue limits the market for that arrangement somewhat, and makes for a more difficult/risky business plan.


Norm

 

What is RCVD?

 

The Millikens' book "Race Car Vehicle Dynamics". Pretty much the standard reference for understanding suspension behavior. Hardcover, almost 900 pages long, and worth every penny of its ~$100 price tag if you're into a deeper understanding of this sort of thing than one or two "cookbook" mods for one specific chassis. Available through the SAE bookstore.

Norm

 

I've got a real problem with my sway bar links and need help. At 70,000 km, I started to hear a rattling noise going over bumps. I took it to the dealership and they told me one of the sway bar links was shot. The replaced in and the problem was solved. At 100,000 km, the same problem occured. I took it to a mechanic I know and he said the sway bar link was gone again. He told me that the links looked far to flimsy for a vehicle the size of a max. I asked him to look for a aftermarket swaybar and links and haven't heard back yet. Are the links prone to failure and what should I do?

Thanks,

Craig

 

Good info, thanks! Will try to get my hands on a free copy of this book. Hope it exists. lol

 

the links are about the same size as the rest of sedans of the same weight. they cost about $25-40 a peice, and take about 30 mins to replace. think of this are regular maintanance, like an oil change or brakes. some people experience failure, and some dont. these cant really go "bad" the ball joint is grease filled, and if the rubber boot gets torn and the grease leaks out, they may lock up. it's very difficult to have these fail in the first place. you may be able to get swaybar links from an autoparts store that dont use a grease filled ball joint, and will not leak. this is the only point of failure that i can see. i am not sure your mechanic is correct in his diagnose.