RS-R sway bar vs Tri-Point sway bar (engineering based discussion)
 

Just thought I would ask the suspension and engineering gurus that hang out on this forum. That, and I want to encourage some more in-depth discussions about suspension in this part of the forum.

1) Here is the RS-R adjustable sway bar (currently only available in Japan and no RX-7 application yet).

http://www.rs-r.co.jp/products/stabilizer/index.htm

http://www.rs-r.co.jp/products/stabi...stabi_main.jpg

My understanding is the you can change the "stiffness" of the bar, by turning the knob.

http://www.rs-r.co.jp/products/stabi...bi_dial_up.jpg

I'm curious as to HOW this works. As in, is there another bar that is found inside of the sway bar,...that slides in certain positions to provide more strengthening, thus providing a "stiffer" bar? Or maybe it is a bar w/ a piston inside (heard this rumor).

I spoke w/ the guys at RS-R (USA), and they were not fully up to speed w/ the engineering aspect of this product. So, I figured I would ask here. I'll find out the info sooner or later, but I was curious...

2) Tri-Point Modular Sway Bar

http://www.tripointengineering.com/G...n/antisway.gif

Adjustment of the bar, is made along the ends of the bar (at the brackets).

3) Whiteline Adjustable Sway Bars (not for RX-7 application, but used as an example).

http://www.pdm-racing.com/products/i.../pdmlinks3.jpg

Adjustment of the bar, is similar to the Tri-Point bar. Adjustment is made along the ends of the bar (the bar itself).

---------------------------------

Essentially, I would consider the designs of the Tri-Point and the Whiteline bar to be the same. But the RS-R sway bar has me curious. What do you guys think of the RS-R sway bar?

BTW, how do you guys like the Tri-Point sway bar?

Any advantages/disadvantages of one design over the other? Just curious...

I don't know for certain but here's how I bet the RS-R bar works. The bar is actually split where the adjustment mechanism is. Each end inside the mechanism is somehow preloaded with a cam that is adjustable. You increase pressure on the cam and the bar becomes more "solid". You decrease pressure on the cam and the bar ends can twist more in relation to eachother where they meet inside the joint because they could essentially "slip". Similar to the "active" hydraulic bars I believe Citroen used in the WRC and BMW uses in the new 7 series.

The other bars as you mentioned are adjusted by changing the lever arm length of the blade arms.

The only other adjustment mechanism I know if is the blade adjustable sway bar. This bar effectively adjusts stiffness by the blade itself deflecting. The more the blade deflects the less force actually goes through the torsion bar which makes it "soft". As the blade it rotated it becomes more stiff and transfers more force into the torsion bar and so it becomes "harder".

As for advantages/disadvantages I would expect the RS-R bar to be more application specific because I bet the range of adjustability is less than something like the Tripoint for instance. On the plus side you just have to turn a knob as opposed to disassemble the joints to adjust stiffness. I can think of others but that would sum it up overall for me.

Somehow...I knew you (Damon) would be the first to respond. haha

I think its the blade type - I know SARD makes some dashboard adjustable sways and it rotates a blade type mechanism. I guess the easiest way to describe it is by using a yardstick - one direction it flexes very easily, almost bowing it without much effort, but when you rotate it 90 degrees and use that same motion, it is extremely stiff, and would snap before reaching the same deflection.

yeah i agree with damon. i think the tripoint bar (which i have) will definitely have a greater range of adjustability. however, the rsr might have better resolution meaning it's difference between adjustments could be smaller.

a couple more things...with the tri-point bar you can adjust it very easily w/o getting under the car too. there are also 4 thickness options for the center bar that can increase or decrease the stiffness based on your application. i'm using the 0.188" one which is the 2nd stiffest as i remember. the road racing one is one up from that and they can get you an even thicker, stiff one that is hardly ordered.

Okay...given the the Tri-Point bar can be ordered in a range of thicknesses....

Instead of increasing the thickness of the bar (to gain rigidity), couldn't you instead go w/ a bar that is of a fundamentally stronger/stiffer material (to gain rigidity)?

Example:

Instead of increasing the thickness, you instead change the material of the bar. From chromoly (sp?) to titainium for example? (I do realize that changing an entire bar to one of a different material, is more costly than changing just the thickness.)

Second question,...is there a point where a sway bar can be too stiff (and any dangers associated w/ this)? Assume that you can create a bar that is of a "magic" material that does not bend whatsoever.

Yes you can do that...

Torsional Stiffness = JG/L

where J = polar moment of inertia
G = Sheer Modulus
L = length of bar

However it is not that simple. You have to look at the safety factor as well, the yeild strength of certain material may be too little and give you the a safety factor of less then 1 if you divide the max torisional stress by the yield strength of the material.

There are several ways of creating antiroll bars.

You can change the blade length, the longer the length the less angle the bar will twist, which in turns decreases the torsional stifness, you can change material, you can change the length of the bar, you can change the polar moment of inertia.

J = (Pi/2)*(Outer radius ^4 - Inner radius ^2)

Also remember that torque is defined as...

Torque = theta*J*G/L

good luck.

Also you should not arbitary buy antiroll bars unless you can figure out what your roll rates for your car are. Specific bars are designed for specific spring rates.

You can do a lot of your own experimentation with some paper clips. :)
This helps me a lot in trying to get a hands-on way to understand how bar configuration affect stiffness.

That RS-R bar, as DamonB correctly mentions is splined, so the length is adjustable via the knob.




-Ted

Do swaybar prevents the inside wheels from lifting off the ground?

Yes, a swaybar or antiroll bar acts like a spring that links the left and right wheels together. The antiroll bar distributes the forces from the inside to the outside tire, essentially making a independent suspension less independant.

From out stickied link list:

Everything about Sway Bars by Grassroots Motorsports

In that case, if my inside wheels are already lifting up, I don't need stiffer swaybar right?
see photo below. I have stock swaybar with widefoot mount and mazdatrix end-links.
http://www.berudu.com/rx-7/Photos/20...b/IMG_3111.JPG

a stiff antiroll bar will transfer more lateral load... therefore the lifting tire will get more load and hold it to the ground

any answer to the question?

Read the link I posted earlier and concentrate on "The Effect of Anti-Roll Bars Upon TLLTD" part.


There are lots of reasons the inside front could be lifted and they don't necessarily mean the car needs more/less front bar.

The car could have more roll stiffness in the front than the rear so as power is applied the car squats down and twists at the rear but can't at the front, so more weight transfers off the inside front tire and it lifts some.

The car could be in a fast transition manuever (or te inside front hit a bump) and have too much rebound on the front shocks so the shock doesn't allow the inside front spring to return quickly enough and the inside front doesn't stay down.

The car could have a coilover kit with springs that are too short and so rattle in the perches. Therefore the suspension cannot operate at full droop because there is no spring left to push the tire down in contact with the road. Therefore as the car rolls and the inside goes into droop once the spring leaves the perch the tire is doing no work at all and merely "hanging" from the damper. The spring transfers force between the tire and chassis; once that spring is out of the perch and doing no work, neither is the tire. (Don't believe it when people say it's okay for springs to leave the perches when you jack the car up. Your giving away suspension travel in droop and thus grip because you have springs that are not of the correct length for your dampers).

The car could be headed across an off camber portion of track. The rear tires are on "level" ground and the fronts are already on the off camber portion so it makes the inside front appear to be lifting.

The car could have a lot of front roll stiffness and less rear. So much so that the outside front has enough tire grip as to use up all bump travel due to chassis roll and the front bar is so stiff it actually lifts the inside front as well. This is easier to do than you think if the springs are too soft.

The car could be in a right turn under hard acceleration and have little rear shock in compression but lots of front rebound. Therefore as the car easily squats the front takes slightly longer to settle than the rear.

In short, ignore the picture. You need a front bar that will allow the most work to be done of the tires and that will also balance with the rear to make the car neutral for its given setup. That question can only be answered by driving the car.

I run a much stiffer front bar than stock at most times but on race tires I can still generate enough grip to roll the chassis and fully droop the inside front under hard acceleration. Keep in mind this only happens under hard acceleration and therefore I in fact don't need the front to be doing as much work anyway; the hardest cornering part of the turn is over.

Here's a pic from a couple years back carrying the inside front. The exit for this turn is slightly off camber and at the same time the car is under a lot of power.
https://www.rx7club.com/forum/attach...&postid=592318

Here's a shot from two weeks ago. Same front bar setting as the above pic. Car has crested a hill in the middle of the turn and has not yet settled. Started down hill and accelerating gently.

https://www.rx7club.com/attachment.p...postid=2903293

well, there are tons of reasons that the inside tire on tight turn could be lifting. the front may be too stiff causing the tire to life or the back compression may be too soft allowing the opposite side back shock to compress too much (remember the suspension works diagonally).

BUT, from driving your car so damn much I have to say it's time for the Tri-Point Bar :D That's what by butt accelerometer feels....but you never listen to me so whatever....

damon, I read that link before I posted. I don't get anything out of that link. Sounds like a guy BS-ing to me. No clear fundemental laid out.
But your explanation kinda make sense.

alex, Your solution is to spend more money...not yet..I am a cheapo...
I think the spring 675 front and 500 rear are stiff enough that stiffer swaybar may not work well. But of course, after you change your spring to 700, I think the tri point swaybar still has some effect.

sway bars effect the speed that lateral weight transfers.

sway bars do not change the amount of lateral weight transfer.

if you have too much bar, the car will be very difficult to drive at the limit. it will break away before you are ready to deal with it. it will be slower.

for any strut type car, like a bmw or most porsches, body roll is death as 3 degrees of roll in a corner means 3 degrees of lost camber. as a result, strut cars have to run too much bar.

not so w the race car suspensioned fd.
that's why it is a potential killer on the race track. you can run some roll and be able to drive it at the absolute limit without breaking a sweat as it talks to you. that's because the tire is cambered properly even w a 3 degree body roll attitude. you can clearly see that by noting how good the outside wheels look camberwise on reza's picture.

as to specific swaybars... if the tripoint is an adaptation of real racing bars it should be the ticket. a straight hollow (read light) tube with splined ends and an aluminum trailing arm w multiple postions... if you need to go up or down alot you just switch the tube which is offered in varying wall thicknesses but the same outside diameter.. if tripoint's bar isn't hollow i would call Stock Car Products and do a bit of engineering.

i always found more time was in finding the right spring rates and shock settings and never changed the front bar once i found something that worked. generally rear bars are for tuning oversteer-understeer.. the last thing the fd needs is more rear bar/rear roll stiffness. i did have a cockpit adjustible (blade) rear swaybar in my gt3 mazda which i used towards the end of a race to compensate for 60 pounds of gas that had been burned.

as to reza's cool photo... it is actually getting alot of grip in the wet. the inside front tire is a bit unloaded which is natural and is a result of being on the power and compressing the diagonal spring... the rear outside.

'apologies for a bit of rambling but did enjoy the photos.
howard coleman

I've got some other pics but the server is puking right now.

reza, you in essence want to run the car as stiff in roll as possible without giving up grip. The stock FD springs are too soft for best performance on race rubber and that's why we counter that with stiffer anti roll bars. However the same car with stiffer springs won't need as much bar all else equal. Don't judge the car by how much lean you have, judge it by total grip and front/rear balance.

ok, that's it....let's just swap my sway bars over to reza's car for a couple of autocrosses after our national events in may. then we'll get some real before/after results. "just do it".

Same turn. Car has come down the hill but is now accelerating harder. More squat at rear and therefore the inside front is near fully drooped.

https://www.rx7club.com/attachment.p...postid=2905394

Same weekend; my gf boogying the car through one of the fastest turns. It's off camber once again and she has both inside tires nearly unloaded as the car is steady state for a moment in the turn. You could never do this unless the tires have lots of grip, otherwise they would slide rather than load up the chassis to such an amount.

https://www.rx7club.com/attachment.p...postid=2905402

Damon, you went to the national in houston, right? How was it?
What kind of tires are you running?

Those last few pics are from the Houston NT. There were 11 SS cars there; 9 Z06 on Kumho 710's, 1 Z06 on Hoosiers and my FD on Victoracers.

I feel I drove poorly the first day; my first run was awful on that surface. Made some pressure changes and the car was much better but I couldn't begin to approach what the vettes were running. I drove much better Sunday but was left in the dust once again. Quite a few course workers and spectators said I was flying (Geez! says my Sunday runs were good too) but I just cannot put the power down like the vettes can, especially on that course with the hills in it. It was a great course and I really enjoyed it; it payed off bigtime if you were both aggressive and precise. I just was no threat whatsover to the Z06 drivers on that course.

Houston NT results here

Have you try Hoosier?
Alex has them hoosier, they stick very good in corner, and the turn in is fast. Plus if you feel its going to slide, just put more throtle and it hook up straight like arrow...
I was going to order V710, but got Victos instead. The victos feel vague and slow turn in response. You turn, then it pause, then starts turning later...

You're speaking portions of a second when you're talking Hoosier or 710 vs a Victoracer. No sense in my spending lots more money for Hoosiers only to loose by 3 seconds instead of 4 in Houston; no tire in the world is worth that kind of time.

I'm more pragmatic and realistic in my setup choices for the car. The Z06 drivers I outrun locally I will continue to outrun. The ones beating me usually put over a second on me. Switching to Hoosiers is not going to get me that second back. They have more grip than the Victoracer, but not enough to make up that kind of time. In the end I would spend more money to run Hoosiers but finishing position wouldn't change; no sense in that. If I were already in a Z06 the story would be different.

all fd's in ss are now in a rut because of the power advantage and lack of rubber. those ss z06's are probably running 265 in front and 315 in back? combine that with 400 hp and our little 10 yo car is at a big disadvantage.

when reza is talking about the hoosiers there really is a big difference. part of the difference is running the extremely low 30 series profile on 18" wheels. add to that the additional stiffness of hoosiers and extra 2" of rubber on each tire with the 285 width and you've got a whole 'nother ballgame :D there really is a huge difference in the limits. i'm sure if you just bolted some 18x10's on you could gain another 1-2s on a 60s course. time to move to street mod 2 or asp right :)

street tires to race rubber are day and night.
victo vs hoosier are morning and afternoon. :)
I had 2 year old hoosier, alex got ecsta previously then hoosier. Now I got victos.
And we have been using the different tires on different car, almost all combination now.
A subtle difference is that 17" vs 18". The 17" seems to be more forgiving

ASP is useless because the Z06 is also in that class; street prepared mods are not going to close the gap to a Z06 no matter how big a tire you put on the FD.

SM2 is even worse. Unless you have lots of money to dump into an RX-7 you will not be nationally competitive. The FD no longer has so many intrinsic advantages compared to other cars like it once did.

At some point you just have to realize you're racing a car that is more than 10 years old. You can't overcome that unless you go into a Prepared class and essentially cut the car up and throw away most stock pieces. That's what it takes to be nationally competitive in those classes.

i disagree that the fd is useless for ASP. although we will never have more horsepower than them autocrossing as we know isn't always about horsepower. the fd can definitely be nationally competitive with the right setup and driver. my car is far from prepped to the max of the rules (stock cat, a/c, passes smog, sunroof, etc.) and we don't do bad for two relatively beginning drivers.

so what if the car is 10 yo? the lotuses in our class are almost 40 yo and have maybe 140HP. are they still right up there? yes.

while we might not be able to whip anybody you can't say the fd is useless in asp just yet...i know ss is a different story though. i agree with you about street modified classes though, they are starting to be a playground for those with more funds. BUT, wait till you see andy mckee in the old tri-point fd in sm2 at nationals this year. that car is fast! i can't wait to see how it does against some 3-rotor competition...

just remember like life motorsports isn't always fair. sometimes how fast you wanna go depends on how much $$$ you wanna spend. jeez, gotta go buy a lotto ticket now ;)

alex

imo the turn-in on the 18" hoosiers is way better than 17" kumhos. i like they way they feel better too. can't complain about the treadlife of the kumhos though. we'll have to see about the v710 though. a3s04's are next :D

With all due respect to everyone involved there is a chasm of difference between being regionally competitive and being nationally competitive. I've trophied in SS no worse than third each season since I started but I won't begin to tell you that's the same as doing it at a National Tour or in Topeka. You understand the difference once you see what the national trophy winners are capable of.

I love racing my FD and will continue to do so but ASP is no stomping ground when the Z06 is still present. All the advantages the Z06 has in SS over the FD it still has in ASP, with the exception that the FD can have more tire than it can stock. Tires and springs are not going to turn the FD into a Z06 killer in ASP. It absolutely will not happen.

i totally understand what the really really fast guys can do and been to multiple national tours. but i'm going to tell you that it is possible. i'm not saying the fd with equivalent driver's is going to drill the competition by 2s over 2 days but at least stay within trophy range. yeah the fd can have more tire but it can also generate more power and do some weight loss at the same time. the z06 is an incredible car in ss trim (power & rubber) so its gains are fewer in sp.

You sure you understand what is legal and what is not in SP? ;)

Exactly, I don't think you can even get an ASP FD to the same power levels of a SS Z06, legally.
I'd love to see an BP FD. :D
Back to sway bars:
I feel that sway bars are over used in suspension tuning. And it's because they are so easy to replace. Most of the time stiffer springs are what is needed (depending on the handling problem of course). And generally, if you are picking up the inside front tire it's because your front bar is too stiff.

Since both cars can be modded in a similar manner, I don't see how the FD is going to gain significant ground on the Z06 in ASP.

I agree. But in stock classes you're stuck with the stock springs, so the front bar and the shocks become VERY important since that is your only means of tuning.

You're right though. If the car needs so much bar that should tell you that something with the springs isn't quite right...

Back to my car:
I have 675# spring front and 500# spring rear with the JIC FLTA2 coilovers.
And I am using the stock front swaybar with Mazdatrix Links and Widefoot mount. And stock 93 rear bar.
There is no softer front bar than stock right?
My understanding is softer front bar will induce oversteer as well.

reza what is the car doing poorly right now? You've got adjustable shocks, use 'em!