I have been into handling since I was into cars....My first "car Love" was a Pantera, and then my Father told me about his (British) sports car adventures.....So I have been thinking of how suspension works for a long time.....To give you an idea of the amount of....(probably useless) knowledge I have rattling around upstairs, go look up "De Dion suspension"....
There are a bunch of different things that make one car a "good handler" and another.....simply clumsy- or dangerous! One of these is the balance of traction in a turn....A situation where the front slides is called understeer, and one where the rear washes out is called oversteer....Of course, throttle position, steering input, etc all have an affect on that balance....
I don't particularly like Porsche 911s but realized that Porsche did car development properly; They take a platform, and then develop it, piece-by-piece, to perfection. The 911 has the engine way out back, creating a rear-heavy weight balance, which leads to Drop-Throttle-Oversteer (DTO), which refers to the habit of 911s (And other rear-heavy cars) to swing their rear out when you cut the throttle in a turn....The more heavy the "Butt", the more rapidly the rear swings out. Usually, you have to balance between good turn-in and DTO....the better the turn-in, the worse the DTO and of course, vice-versa. Porsche addressed this problem with their "Weissach axle", which uses suspension geometry to change the angle of the tires during acceleration and deceleration. I found this fascinating, but at the time I was playing with a 1973 Mustang w/5.0.....Obviously, it has a solid rear axle, so you can not do anything to affect toe-in/out....
But my mind kept twisting and turning and I finally came up with a (Relatively) crazy idea; Make the stabilizer bars vary their strength.....At first, I only used different mounting links......I installed Poly bushings on the rear bar, then went to a bigger front bar (From .875" up to 1.125") but mounted it with regular rubber bushings...(I also seriously revised the front-end alignment...Getting approx' 3.5 degrees of caster and 1 degree of camber).
The idea is that as you first turn in, the rear bar acts immediately, but the front bar is still working thru the rubber bushings, causing the handling balance to go more "Over-steer" and giving you good turn-in.....Then, as the car takes a set at max "G", the body rolls farther and the front bar starts to work and, because it's much thicker than the rear, it backs the car's balance off towards more understeer, which is more stable, and also allows you to put more power down on corner exit.
The Mustang handled better than my 1999 Firebird Formula.....It had superlative turn-in, yet on turn-exit, you could really get on the throttle early and hard. A friend of mine who knew Carroll Shelby and has owned a 429 BOSS Mustang and a Mangusta (And raced a 67 Cougar in Trans Am) was really impressed by the handling.
Later, I came back to my 85 Fiero SE V6...At first, I installed a 3.4 F-body engine and Getrag 5 speed, and also an 88 rear subframe/suspension, which was a big improvement all on it's own...And the addition of the rear stabilizer bar did improve balance- still, I wanted more.....So I changed the end-links in back for Rodney's solid links...This was a good improvement, but I wanted to see how far I could take my concept. I had recently theorized that stabilizer bars vary in stiffness vs the angle they are at; Think of a bar with it's arms horizontal vs the vertical movement of the end-links....The bar is at it's softest at this point...Now, angle the arms up to, say 30 degrees, but the thrust of the end-links is still (Basically) vertical...The bar actually twists a bit farther during suspension deflection, which makes it appear stiffer.
I decided to use the Fiero's brake dive and acceleration squat to vary the bars strength....I used longer end links on the front to angle the bar ends up (Dive =Stiffer/Squat = softer), and in the rear, I made new brackets to locate the end links higher(Also used RD shorter end-links) while drilling the frame-mount holes 3/4" lower (Dive = softer/ squat = Stiffer)....I was able to angle the rear bar at 14.5 degrees, but was limited(So far) to 12 degrees up front....I may create spacer-blocks to move the front bar frame mounts down 3/4"...(I should add that drilling those rear frame mount holes any lower would cause interference between the bar and the subframe rear crossmember).
The car has what I call "telepathic turn-in" (In fact, the first time I drove it after the mods, I swear it felt like it turned in BEFORE I turned the wheel (Yet it is stable straight ahead!), but at the absolute limit in a turn, if you jump OFF of the throttle, it just tightens the turn a bit (What you want it to do!) Most mid-engined cars are not "Tossable"- they want to follow one line thru a turn and if you are off just a bit, you are much slower and feel "out of shape".....This car feels very neutral all of the time, and jumps to command from the wheel, with the throttle at any position. I have pics that will be posted later.....(Thank you Ron!)
My car is lowered approx' an inch......The roof sits at almost exactly the same height as stock....But I have taller tires (205/55 & 225/55-16)......Stabilizer bars can tend to confuse people a bit.....I suspect that some cars get their odd/spooky handling because the bars are mounted to do the opposite of what mine are doing..
Although adding bars increases the road-holding of a car, when tuning your front-to-rear balance, you make the bar bigger(Stiffer) at the end that sticks TOO good.....If the car pushes (Understeer) then add a bar to the rear (Or go bigger)......If the rear comes around too quick/easy, increase the front bar size. This little detail can really confuse people because it sounds contradictory....
And yes, I spend too much time thinking about suspension....(I will admit to having very little understanding of roll-centers)......
Originally posted by cvxjet: I decided to use the Fiero's brake dive and acceleration squat to vary the bars strength....I used longer end links on the front to angle the bar ends up (Dive =Stiffer/Squat = softer), and in the rear, I made new brackets to locate the end links higher(Also used RD shorter end-links) while drilling the frame-mount holes 3/4" lower (Dive = softer/ squat = Stiffer)....I was able to angle the rear bar at 14.5 degrees, but was limited(So far) to 12 degrees up front....I may create spacer-blocks to move the front bar frame mounts down 3/4"...(I should add that drilling those rear frame mount holes any lower would cause interference between the bar and the subframe rear crossmember).
By my math, 14.5 degrees changes the force by 3.3% and 12 degrees by 2.2% for a total swing of 5.5% in the roll couple distribution. That's enough to shift from mild understeer to neutral for most folks. Interesting idea.
Mender...You got my brain smoking a bit.....With the stabilizer bar arm lengths (Front 8.5", rear 12.75") I figured approx' 0.15" per degree front and 0.22" per degree rear.....Considering 4" of total travel (Full up to full down) you get approx' 27 degrees of arm angle change up front and 18 degrees in the rear. EDIT>>>(The front bar mounts to the A-arm inboard of the BJ.....So the front 27 degrees should read 22-23 degrees! (Thanks Mender!)
Obviously, brake dive and accel' squat are not going to have that big a change, but the two ends cumulatively can affect handling......I wish the local Fiero groups would have "track days" cause I would like to allow a few people to test drive this car and see what they think......I like to think I am pretty confident in my....smarts.....But a couple of times I have noticed a certain.....lack.....of fully integrated brain cell activity.......
Hey 2.5, I actually had a "85-87 rear bar" for years but never installed it- I was not impressed with how low to the ground(Under subframe mounting) it was.....Maybe there are better designs out there...I wonder what Addco has for the Fiero?
[This message has been edited by cvxjet (edited 12-05-2017).]
Don't forget the sway bar links don't move as far as the wheels. Front motion ratio is around 0.7 and rear will depend on whether you have the links on the lower control arms or on the struts.
I'm using a set of Herb Adams sway bars: 1.025" front linked to the factory locations and 1.25" rear mounted to the lower control arms.
[This message has been edited by mender (edited 12-05-2017).]
Rats! I shoulda caught that, Mender! The front is a percentage because it is mounted partway out on the A-arm, while the rear is mounted directly to the strut.......Calculations will resume.......Where'd my note pad go...? (That is PAPER note pad!)
I have been into handling since I was into cars.... I have been thinking of how suspension works for a long time...
Okay, I'd love to get your (and anybody else's) feedback on how replacing OEM rubber sway bar mount bushings with poly bushings affects handling. I've been led to believe for years here that poly sway bar bushings would help stiffen the suspension. When I stated this in a well known Subaru forum, I was "schooled" by a member there who insisted that rubber bushings effectively increased the sway bar's diameter (compared to poly) due to the rubber bushings "gripping" the bar. In all the years I've been here at PFF, I don't recall this argument ever being put forth.
The fella who wished to "school" me appears to be educated on the matter, but I'm also familiar with the expression... bullsh!t baffles brains.
I'd appreciate it if several of you could have a look at This thread. My user name there is Vancouver98STi, and the action picks up at post #8 (although I first appear in post #4). My nemesis in this thread is mrsaturn7085.
quote
Originally posted by mrsaturn7085:
...the factory bar twists the rubber bushing in place. Aftermarket urethane allows the bar to freely spin in the mount. The rubber resists twisting which increases effective diameter slightly. Free rotation in the bushing (urethane/bearings) reduces twisting resistance.
Once the discussion on this starts, it goes on quite a bit... but I believe it's entertaining, and maybe even informative!
Have I been mistaken all these years? Please let me know.
[This message has been edited by Patrick (edited 12-07-2017).]
Good question that you asked about the actual amount of surface movement of the sway bar at the mounts. It's about 1/8" for the average sway bar.
You might want him to up the input loads and allow the rubber bushings to deflect as they normally would in a car, ie, the side going up crushes that rubber bushing and vice versa on the other side, adding non-effective deflection to the equation. 10 NM is about 7 ft.lbs which is a very small force. Resisting 2 degrees of roll in a 3000 lb car with a centre of gravity that is 17" above the ground, a weight distribution of 53/47 with a 5% front roll resistance bias and has a track width of 72" while acting through a motion ratio of 0.5 is the range you want to ask about. Then ask how much reduction in force the crushed rubber bushings would account for compared to non-compressed bushings under the same conditions, and what the relative sway bar diameters would be to compensate for that crush.
I'm curious to see what he comes up with; could be that he's right.
Eliminating the sway bar mount deflection and also the end link deflection by using urethane or solid material allows the sway bar to be effective as soon as the car starts to roll. While the different durometers of rubber available can be used to tune the sway bar effectiveness via compliance, I prefer to go the simpler route and sidestep the issue by getting rid of the rubber. I don't think he would disagree with that.
[This message has been edited by mender (edited 12-07-2017).]
Ummm. Fiero sound- That is a very good graphic....I had a similar one from Addco years ago (Around 1980)....
Patrick......That is just bizarre......Some of the odd things people come up with in discussions about handling.....are WAAAYYYYY out there! I remember one of my teachers in HS telling a group of us car nuts about how his Saab had suspension that "Folded up under" so it could go around turns on gravel just as fast as on asphalt! Even at that age I could see that was BS....
I try- but am not perfect!- to always be as objective as possible...The first mechanic I felt I could trust would say- Often!- "I don't know" when asked a question....If you don't admit you "don't know".....Then you never learn new info!
Mender- There is some affect via rubber bushings rubbing on suspension parts....Some older suspensions (Especially leaf-spring) would sit "high" and "low" because of friction in the system...And of course, there is deflection of rubber bushings.....Something I am using to vary the start of front stabilizer bar affect.
[This message has been edited by cvxjet (edited 12-08-2017).]
2.5.....I don't think they are referring to wing stanchion height....I think they are referring to a "kick-up" style spoiler...Higher- like adding a wicker-bill.......I have another post I want to do about aero.....And one of the diagrams shows how having the Fiero wing too low CAN negate it's benefits by moving the low-pressure area underneath the wing too close to the decklid...causing lift there....I don't think the Fiero design would suffer from this though....
Originally posted by Patrick: Once the discussion on this starts, it goes on quite a bit... but I believe it's entertaining, and maybe even informative!
Have I been mistaken all these years? Please let me know.
Patrick,
No way! The theory that it increases diameter because the rubber "grips" the bar would probably cause such a small amount of difference it wouldn't even be measurable. On that note, even if it did make a difference in the slightest, it would only be a verrrrrrrry temporary phenomenon; as the rubber "gripping" the bar has such a small contact area that it would slip rather rapidly. (I.E. putting a skinny bicycle tire on a 400 HP Corvette, fatter tires are needed for the forces exerted) One should also assume that the sudden flex of the softer rubber would cause part of the bushing to lose contact with half the bar, on the loaded side of the bushing mid turn...
It's nonsense IMO. If he wants to make that claim then I need more evidence than just a theory of what probably happens under ideal conditions.
More "what ifs"; take for example a 35mm sway bar will flex the same amount as a 35mm sway bar every time, no matter the bushing it's sitting in. by that similar logic, one can argue that we can simply weld together a bunch of beer cans and use that as a driveshaft. This theory will obviously not work, the cans will fail and twist into a mangled mess the second you press the gas pedal; why? Because the amount of metal used is too thin are not strong enough to handle the force, the only way to combat that is more thickness, IE strength to deal with the forces exerted here. While not exactly the same point he is trying to make, a rubber bushing "gripping" the bar won't make the bar twist any less, the only thing to do that would be more metal, a 37mm sway bar, for example, 2mm more metal of which will flex less every time compared to the 35mm.
I'm rambling at this point. What a terrible example. I hope you get my point, though.
------------------ "Discord" Red 1988 GT under restoration!
Nice read, track time would be good if you want to learn how to drive your car hard. The fiero's had a chance to drive on new smyrna speedway in central Florida. I had fun. Sway bars, Rodney dickmans endlinks and good driving let's you go home in one piece.
Just an update; I made a 1/2 inch spacer for the front stabilizer bar frame mounts, which angled the bar from the previous 12 degrees to 15 degrees.....The car turns in great and has extremely mild DTO...
I can hardly drive the car at the moment because of Drug-induced Lupus; The doctor prescribed Omeprazole for my acid-reflux, so now I cannot go out in the sun at all and my joints are all wrecked......Supposedly, I will recover 6 months after stopping the drug.........8 months and still no improvement.....
[This message has been edited by cvxjet (edited 01-24-2020).]
cvzjet - had not previously read through this thread regarding your theories and suspension modifications, but WOW! Very, extremely, impressive. Also the contributions from other forum members were excellent. I will definitely save this one and use it for reference when I attempt handling improvements. Regarding your note at the end of your last post ... my condolences regarding your medical condition and I sincerely wish you a speedy and full recovery.
You are welcome GTO........I think it makes the car much more enjoyable to drive- The steering just feels much quicker (It is still heavy at parking speeds)
I forgot to mention that moving the bar down would interfere with the front crossmember braces- So I bought Rodney's braces which are stronger yet smaller in cross-section....
[This message has been edited by cvxjet (edited 01-25-2020).]
Came across this thread and I must admit that it is very interesting for us who trackday our cars. My car has '87 suspension all round, but with an added rear swaybar. This swaybar is fitted underneath and is very close to the subframe and with quite short links to the arms. I don't see how to increase the angles without having ground clearance problems? However, the addition of this swaybar dramatically improved handling and I can really "punch it" hard on corners without spinning out. I do have a certain amount of body roll never the less:
I will be testing the spacer block mod on the front swaybar - one day soon! I made my own front subframe braces, so no problem to modify them.
I'll post my comments to this thread that I made in a different thread:
quote
Originally posted by Z3SpdDmn: That was a good read and good experimentation on your part. I believe the result of your experiment could be attributed to having dialed in more understeer via lateral load transfer bias (reducing DTO), but improved turn-in with that much stiffer front bar. Props for coming up with a way to fine tune your bars since you don't have adjustable bars with various holes to easily affect the overall stiffness and resulting lateral load transfer bias.
I've been through this type of tuning on OEM work (I was the vehicle dynamics performance engineer on the Charger/Challenger/300 a couple years ago). For example, in a package I was tuning for the Challenger R/T, reducing the front bar stiffness resulted in a slower initial steering response, but reduced understeer once the weight transferred.
In the case of bushings, they're effectively only changing the response of the bar to the input. Not so much outright rate. There was some discussion on rubber bushings adding rate and "bonded" bushings are used in some OEM applications to add rate to the bar without adding mass. In non-bonded bushings, like ours, they would only affect response and compliance.
Also note that in pure pitch and dive scenarios, the bars are not in the picture at all because both sides move together. They do not add any spring rate. I'm not sure if that was fully understood or not from the post.
Originally posted by Patrick: Okay, I'd love to get your (and anybody else's) feedback on how replacing OEM rubber sway bar mount bushings with poly bushings affects handling. I've been led to believe for years here that poly sway bar bushings would help stiffen the suspension. When I stated this in a well known Subaru forum, I was "schooled" by a member there who insisted that rubber bushings effectively increased the sway bar's diameter (compared to poly) due to the rubber bushings "gripping" the bar. In all the years I've been here at PFF, I don't recall this argument ever being put forth.
The fella who wished to "school" me appears to be educated on the matter, but I'm also familiar with the expression... bullsh!t baffles brains.
I'd appreciate it if several of you could have a look at This thread. My user name there is Vancouver98STi, and the action picks up at post #8 (although I first appear in post #4). My nemesis in this thread is mrsaturn7085.
Patrick, as I stated in another thread, some OEM applications include "bonded" bushings, so that the bushing is actually adhered to the bar. The twist of the bushing adds some rate to the bar, allowing the bar to be slightly smaller, lighter, quieter, and cheaper than if it twisted freely. This would also add a little bit of spring rate when driving straight ahead, where a swaybar is normally decoupled from the springs in a straight line.
I am not aware of any aftermarket applications of bonded swaybar bushings. It requires knowing almost exactly what the static ride height will be (and not modifying it). Otherwise, the bushings would be in a constantly stressed state and they would create a variance to the bar rate as they passed through their neutral position since the bushing's neutral position wouldn't coincide with static ride height.
Please let me know.
