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| My stabilizer bar mounting theories.... (Page 1/3) |
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cvxjet
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DEC 03, 09:15 PM
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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!)
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Rsvl-Rider
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DEC 03, 09:24 PM
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2.5
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DEC 04, 09:58 AM
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Interesting, its a bit over my head. How much is your Fiero lowered, and how much does that come into play?
Any thoughts on rear bars on 87 and earlier models?
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cvxjet
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DEC 04, 11:30 AM
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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)......
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mender
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DEC 04, 08:13 PM
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| quote | 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).
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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.
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Tony Kania
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DEC 04, 08:16 PM
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Sharing is caring. 
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cvxjet
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DEC 04, 10:11 PM
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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).]
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mender
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DEC 05, 12:20 AM
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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).]
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cvxjet
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DEC 05, 11:47 AM
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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!)
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fierosound
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DEC 07, 11:45 AM
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