[LAbeemer]

Ok it was my understanding the increasing the rear sway bar rigidity would decrease understeer and increasing front rigidity would decrease oversteer. So the object is to balance out both for a neutral handling car. So cars that understeer (e92) would only need a rear upgrade or at least increase the rear rigidity significantly more than the front. Then cars that oversteer would be the opposite needing either only a front upgrade or upgrading the front more than the rear. So looking at the numbers for the kits out there its mixed review whats the best setup. While H&R increases the rear significantly Hotchkis increases the front significantly and increases the rear the least out of all manufactures. I even saw a few post where people only upgraded the front sway bar and thought it was the best??? Then other post where they changed the front and had no effect till they changed the rear witch made a huge difference???? are we testing different cars or is it lack of driving skills or just different driving techniques?????

WOW that was short and sweet in my head, guess I ramble

[stressdoc]

A sway bar reduces the 'tilt' aka resistance to roll. Tightening up the front usually reduces oversteer/increases understeer. Tightening up the rear usually diminishes understeer/increases oversteer. Things get more complicated with the addition of power, limited slip differentials, and uneven pavement.

The H&R set up is likely to result in the inside rear wheel lifting too much, with accompanying wheel spin (if you do not have a LSD).

The Hotchkis set up is more balanced, but still increases stiffness more in the rear than the front, hence reducing oversteer.

The BMW M-sport set up only increases the rear bar slightly (front stays same as regular sport), with the goal of a more neutral handling car.

Changing spring and damper rates, wheels, weight distribution, ride height, suspension travel, LSD, etc. complicate matters.

Off-road, rallye, street, autocross, etc. have different optima.

Suspension designers usually know a lot more than we do. They have tested their systems, refining them to achieve specific goals. Mixing, partial applications, etc. are usually not a good idea.

[ksfrogman]

stressdoc is right. I have not compared the two brands of bars mentioned. However, a few people have actually changed out only the rear sway bar.

There are several threads that were posted on the physics of sway bars, and the experiences of those who have installed it.

To give an example of what happens if you just change out the front sway bar, the sway bar connects the chassis (the main portion of the car that tends to roll or sway) to the unsprung portion of the suspension via connecting rods. It also the left and right sides of your car. As the car begins to sway in a corner, the bar shifts the car's weight to the outer wheel. So though the car remains more flat in a turn, the increased weight load on the outer, weigh bearing tire may cause it to slide out more under extreme stress--understeer in this case. More understeer in the front reduces oversteer in the rear, and the converse is true.

Mathematical formulas show that sway bar diameter and stiffness are not linearly proportional, but exponential. That is, an incremental increase in diameter exponentially increases stiffness.

Those of us who initially changed out only the front sway bar (H&R)--because changing out the rear one was much more difficult--found the car still to sway considerably, and plow while turning sharply under heavy braking. It also made the car much more noticeably stiff in the front, especially when going over uneven road surfaces (e.g., speed bumps diagonally). The addition of a stiffer rear bar made a tremendous difference in the flat handling of the car. One can appreciate this when travelling fast around a sweeping on ramp of a freeway, or even making a 90-degree turn in a residential neighborhood at 25 mph. The car will turn on a dime. The H&R set-up still seems to favor understeer a bit if pushed hard under braking. I have tried to compensate for this somewhat with the softening of rebound in the front dampers.

[uberschnell]

I have both front and rear HR installed and just absolutely love what it's done for the car. I also have Koni FSD and an LSD.

Because of a scheduling issue I had the rear installed first and drove the car like that for a while. I hated it. It seemed the car lost it's steering feel in a turn. Best way to describe it is to say that in a sharp turn, as you approach the second half of the turn the normal resistance you would feel on the steering wheel (the car wanting to straighten out) would actually lessen. In other words I felt like if I let go of the wheel the car would be more inclined to keep the turn going instead of straightening things out. Very unstable.

I installed the front bar and that eliminated the problem. Now in a hard, late turn the car will still favor under steer, but far less then stock. I have an lsd so by simply adding power I rotate better so It's actually a nice balance.

I also noticed that on the track I lost a bit of the understeer (pre-hr sway bars) by running a square set up (245's on each corner).

[TSM330i]

One of the reasons I went with the UUC Swaybars is because they are adjustable. For about the same price as the others, you can adjust the stiffness of the bars to your liking. If you want to reduce understeer you have a choice to do so.

Check them out.

http://www.uucmotorwerks.com/CATALOG...30-328-325.htm

I got mine from **********s

[LAbeemer]

Roll Bar Stiffness = C*D^4/(L*A^2)

C = a constant
D = roll bar diameter
L = length of bar
A = length of lever arm

Stiffness increases to the 4th power relative to incremental bar diameter increases.

SWAY BARS:

Stock (solid)
F 26.5mm
R 13mm

Eibach (solid) (e90 only)
F 28mm
R 15mm

H&R (solid)
F 27mm
R 20mm


Hotchkis (hollow)
F 32mm (claim 95 stiffer)
R 16mm (claim 105% stiffer)
"7) Are solid sway bars stronger hollow sway bars?
Answer: No. Sway bars work off of torsional force (twisting motion). Therefore, the material in the center of a solid bar plays little role in the resistance of torsional force. With this in mind, we have eliminated some of the center material and also moved some to the outside of the tube, where it is most effective. In turn, this produces a sway bar that is lighter in weight and just as stiff, if not stiffer than solid. For example, a 1’3/8” hollow bar is equivalent to a 1’1/4” solid. But the 1’3/8” hollow bar is 6% stiffer and 43% lighter than the 1’1/4” solid. "



So its hard to compare the H&R to the Hotchkis because the hollow vs solid design but it seems that H&R would have stiffened up the rear the most and only slightly stiffened the front. Hotchkis stiffened up the front and rear almost equal but smallest increase for the rear. So this would have me to believe the H&R are stiffer all around where as the hotchkis are more equivalent to the Eibach. Both Eibach and Hotchkis increasing the front more than H&R.


Cant find specs on the UUC swaybars??

[Orb]

Originally Posted by LAbeemer

Roll Bar Stiffness = C*D^4/(L*A^2)

C = a constant
D = roll bar diameter
L = length of bar
A = length of lever arm

Stiffness increases to the 4th power relative to incremental bar diameter increases.

SWAY BARS:

Stock (solid)
F 26.5mm
R 13mm

Eibach (solid) (e90 only)
F 28mm
R 15mm

H&R (solid)
F 27mm
R 20mm


Hotchkis (hollow)
F 32mm (claim 95 stiffer)
R 16mm (claim 105% stiffer)
"7) Are solid sway bars stronger hollow sway bars?
Answer: No. Sway bars work off of torsional force (twisting motion). Therefore, the material in the center of a solid bar plays little role in the resistance of torsional force. With this in mind, we have eliminated some of the center material and also moved some to the outside of the tube, where it is most effective. In turn, this produces a sway bar that is lighter in weight and just as stiff, if not stiffer than solid. For example, a 1’3/8” hollow bar is equivalent to a 1’1/4” solid. But the 1’3/8” hollow bar is 6% stiffer and 43% lighter than the 1’1/4” solid. "



So its hard to compare the H&R to the Hotchkis because the hollow vs solid design but it seems that H&R would have stiffened up the rear the most and only slightly stiffened the front. Hotchkis stiffened up the front and rear almost equal but smallest increase for the rear. So this would have me to believe the H&R are stiffer all around where as the hotchkis are more equivalent to the Eibach. Both Eibach and Hotchkis increasing the front more than H&R.


Cant find specs on the UUC swaybars??

FYI, the Hotchkis are solid....the number don't lie but marketing does.

UUC:

F: 26.95 mm adjustable
R: 19.05 mm adjustable

Orb

[Sparky66]

Originally Posted by Orb

FYI, the Hotchkis are solid....the number don't lie but marketing does.

Orb

I don't know where you get your info in relation to Hotchkis, as they are definitely hollow. If you research their site you will notice that bars for the BMW 335 are hollow.



.

[ksfrogman]

Originally Posted by AW325xi

One of the reasons I went with the UUC Swaybars is because they are adjustable. For about the same price as the others, you can adjust the stiffness of the bars to your liking. If you want to reduce understeer you have a choice to do so.

Check them out.

http://www.uucmotorwerks.com/CATALOG...30-328-325.htm

I got mine from **********s

It was my understanding that the adjustable mounting points at the end of the UUC swaybars do not adjust the stiffness, but rather give you the option of optimizing the geometry of how the bar and links match the attachment points.

[ksfrogman]

...and just another aside:

The addition of the rear sway bar (H&R) made the biggest diifference in the flat handling of the car, compared with the stock ones. My car had the sport package plus H&R sport springs and front H&R sway bar already before I upgraded the rear sway bar as well.

[Orb]

Originally Posted by Sparky66

I don't know where you get your info in relation to Hotchkis, as they are definitely hollow. If you research their site you will notice that bars for the BMW 335 are hollow.



.

Hum, do the calculation and you know it is not possible. Modulas of rigidity "G" doesn't change much for spring steels so unless there stiffness numbers are wrong it can’t be…it is impossible.

Remember: D^4 - d^4 for hollow bar.

Orb

[LAbeemer]

sorry orb i had to retake college algebra this formula is a bit beyond my skill level but I will ask hotchkis tomorrow cause if your right that front bar is HUGE lol.

Bummer so the UUC bars aren't adjustable. i would think moving the endlink farther away from the pivot point would effect leverage. longer away being softer and closer being stiffer??

[TSM330i]

Originally Posted by ksfrogman

It was my understanding that the adjustable mounting points at the end of the UUC swaybars do not adjust the stiffness, but rather give you the option of optimizing the geometry of how the bar and links match the attachment points.

Not so. Here is the write-up from UUC's website about the different settings and how the various positions of the swaybar endlinks change the stiffness of the bar.

Setup of the Sway Barbarian

It is recommended that you become familiar with the characteristics of the Sway Barbarian before "pushing it" in higher speed maneuvers. Without becoming adjusted to your car's new handling, you may lose control of your vehicle. It was found on the E36 section, but it still applies to the e90 as well.

After the front and rear Sway Barbarians have been installed, it is recommended that the front be set to FULL STIFF (which is the innermost of the three holes) and the rear to FULL SOFT (holes closest to the ends). This setup will give your car the reasonable understeer with the Sway Barbarians. From there, you can tune the bars to your driving style.

For advanced users, note that you can set the front and rear bar in "middle" positions. For example, the rear E36 M3 Sway Barbarian has two adjustment holes. Conventional thinking would assume that you have two positions, stiffer (holes furthest away from the ends of the bar) or softer (holes on the ends of the bar). For increased fine tuning, you can set one side to soft and the other side to stiff. The vehicle does not know the different from side-to-side when it comes to bar stiffness, so in effect, you have a "middle" position.

Adjustability

Unlike some other aftermarket sway bars which do not offer an adjustable rear bar, the E46 M3 SwayBarbarian use a multi-hole system at both the front and the rear, resulting in a six-position adjustment range. This allows for fine tuning of the bars in terms of their effect on your M3's balance by modifying the effective stiffness of each bar. Not only can you dial-in the characteristics you desire, but the specifics and settings of other suspension modifications, such as spring and damper rates and tire sizes, can be optimized to your taste. For a closer look at how suspension changes can effect cornering attitude, please click here.

The advantage of a hole-based adjustment system is "simple"... very specifically, simple to adjust and tune without any guesswork. Repeatable results after making changes is assured. Use one setting for street use and another for auto-x or track. After the event, an easy change of the attachment hole used puts you back exactly to the street setting. Problems with pre-load and corner-balancing are eliminated.