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Front/Back Sway Bars

An Extra Set of Sway Bars Negates Nose Dive
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Sway bars, also called torsion bars or anti-roll bars, are metal tubes running parallel to an axle and attached on the bottom of suspension mounts on either side of the axle to dampen side-to-side body roll in a car.

If you put an extra set of torsion bars running front to back, between the front left tire and the back left tire and between the back right tire and the front right tire, it would dampen the front-to-back pitching of the car during heavy acceleration or breaking. This would keep the car more stable and lessen the need for high spring rates. It might be way too complex and not worth it, though.

discontinuuity, Jun 05 2005

Chassis explanations http://www.autozine...is/tech_chassis.htm
ULSAB monocoque blurs the distinction between body and chassis. [Ling, Jun 06 2005]

Coupled suspensions http://www.ukcar.co...ion/interlinked.htm
"This system has the same effect longitudinally that the anti-rolling bar has laterally : when the front wheels rise because of a bump, the spring located under the chassis is tensioned and tend to make the rear wheels rise as well." [angel, Jun 06 2005]


       [rasberry re-tart] is the [Farmerjohn] of automotion.
zeno, Jun 05 2005

       Sway bars dont dampen anything and have nothing to do with controling body roll. Left suspension is depressed. That force is transfered to the right suspension via a torsion bar in order to keep the right tire firmly planted on the ground. If your turning left more of the cars weight is placed on the left wheel, taking weight off the right wheel. During hard cornering without a torsion bar, tires would loose traction. If your concern is body roll something like a strut tower brace or a roll cage will help out alot.
10clock, Jun 05 2005

       [10clock], that's a pretty definitive sounding opening sentence. Are you that sure? Drive your car hard in to a turn and measure the body roll. Take off or add sway aka anti-sway aka anti-roll bar(s), drive the car hard in to a turn and measure the body roll. Is there a difference? Are you just making some sort of semantic argument that I don't get?   

       Your description of the action of a sway bar is tough for me to follow. To me, it sort of sounds like you're saying that compressing the suspension on the left side of the car will cause the right side tire to be pushed downward by the torsion bar. It won't. The transferred force will in fact push the suspension upward (compress).   

       My feeble attempt at describing the function of a "sway bar": when a car turns right, the left wheels are more heavily loaded (intuitive physics). This means that the left side suspension will be compressed. The anti-roll (torsion) bar transfers a portion of the compression to the right side suspension, thus trying to compress (push up) the right side suspension when the left side is compressed. The spring on the right side pushes back (down) on the torsion bar which effectively increases the spring rate on the left side. The end result is that the car doesn't "lean" as much when going around a turn. (Of course, this also works with left turns.) The effect of reducing the body roll is that less weight shifts away from the right side. This more even weight distribution means an improvement in traction on the right side tire when compared to the same vehicle not equipped with the anti-roll bar.   

       Now there's a half minute of your life you'll never get back!   

       Anyway, I think the idea could technically work and I too would be surprised if it hasn't been tried. It might make for a rough ride. Just as adding a traditional sway bar increases "single wheel bump rate" side to side, this would do the same front to rear.   

       Having said all of that, well engineered anti-dive suspension suffices for my needs and driving style.
half, Jun 05 2005

       Chassis and body are two very different parts of a car. Torsion bars are part of the suspension, that is part of the chassis. They are not part of the body of the car. This idea wont work.
10clock, Jun 06 2005

       10oclock, the distinction between chassis and body is not clear on my car. One sort of blends in with the other. The anti-roll bar on the front connects to the body/chassis, but the ends connect to the bottom of the Macpherson struts.   

       I agree with half. The normal anti-roll bar will restrict roll, but allow a common (to both wheels) bump to be ridden over.   

       But an anti-roll bar back to front (shall we call it a pitch-bar?) will restrict differential movement front to rear, as rasberry re-tart mentions. However, I believe a bump will not be common to front and back, and therefore will not be easily accomodated (effectively, all wheels will want to move up and down together).
Ling, Jun 06 2005

       [10oclock], your argument seems to me to be orthogonol to the idea and to [half]'s explanation.
bristolz, Jun 06 2005

       //the distinction between chassis and body is not clear on my car// -ling. That doesnt make any sense. All cars have a chassis and a body, ALL OF THEM. Why would you want to link up front and back suspensions. The front end doesnt always hit the same stuff that the back end does. For instance, while turning. I would also have to ask what kind of cars your all drive.
10clock, Jun 06 2005

       "I would also have to ask what king of cars your all drive."   

       Does Anheuser-Busch build a car?
bristolz, Jun 06 2005

       10oclock, check the link. Under ULSAB chassis type, notice that the roof is part of the 'chassis'.
Ling, Jun 06 2005

       Please show me a car that has its all of those "chassis" are missing their suspension, powertrain and engine. And since this is a question about suspension systems it would help if you could make a point about suspensions not the body of the car. Lets not get into symatics cause thats where this is heading. The body of the car is still mounted onto a "chassis" "frame" whatever you call it. //Does Anheuser-Busch build a car//-bristolz. Yes they do sponsor a nascar.
10clock, Jun 06 2005

       In arguing the matter of "chassis roll" vs. "body lean" in the context of a discussion on anti-roll bars:   

       If someone said to me, "Sway bars ... have nothing to do with controling body roll." then I would respond with something along the lines of 'The body of the car is still mounted onto a "chassis" "frame" whatever you call it.' I might have replied with something along the lines of, "Lets not get into symatics cause thats where this is heading."   

       Anyway, those are the types of responses I would have had if someone hadn't beaten me to them.   

       Unibody construction has been around for quite some time now and clearly blurs (eh?) the distinction between the body and the frame portion of the chassis. The body shell itself has become a structural member of the vehicle. It isn't just just along for the ride(r) as it used to be.
half, Jun 06 2005

       The notion of interconnecting front and rear suspension units is not new, having been used on the Citroen 2CV (linky). I assume most of us know how well those things handle.
angel, Jun 06 2005

       Oh, so that I don't come across as completely rude and anti-social, I should answer your question about "what king of cars your all drive". I'm assuming that you mean "kind" and that you missed [bristolz]' little Budweiser joke. Hang on, here's another minute of your life you'll never get back.   

       Well, until recently I had a 1993 740iL; a relatively heavy luxury sedan with surprisingly good anti-dive characteristics under heavy braking and fairly flat cornering for such a big car. I have a 1984 633CSi - also excellent in handling the anti-dive problem and quite fun to drive in general. I have a 1981 300TD (station wagon) that takes speed bumps like no other car I've ever driven (except possibly a massive 1958 Cadillac land yacht). I bought the 300TD after doing the electrical work for a 350 C.I.D. TPI engine swap in a 1982 and seeing how well the little Mercedes had held up over the years. I must admit that the 5.7 liter V8 version we built was much more fun to drive than the 3.0 liter in-line 5 cylinder version. My 1936 Ford pickup, 1950 Chevrolet pickup (both currently in "project" state) and daily-driver 1966 Chevrolet pickup (all without anti-sway bars) have a HUGE amount of body lean/chassis roll, push/plow, dive and every other dirty suspension word that you can think of. I'm expecting that the IFS with power rack-n-pinion that I'm putting on the '50 will make it more wife-friendly in the driving department. The '36 is going to go the same route eventually - after I finish my bit-off-more-than -I-can-chew concrete work and landscaping project which will force me to move the truck out of its back yard storage location (anybody in the market for an original, complete wishbone style, straight axle front end for a restoration?). I'm casually looking for the parts to add a factory sway bar to the '66 - it's by far the worst of the lot. I also have a 2004 Nissan Murano (which I have no plans to modify).   

       No, I'm not wealthy, just stupid and I'm not a mechanic, just a glutton for punishment. You might not like me much, but the auto insurance company does.   

       There are people here who own way more cars and understand WAY WAY more about cars than I do. I mostly just fake it until I find something that works.   

       With the exception of the Nissan, I have done the maintenance, repair and construction on all of my vehicles. As best I have been able to tell, the body lean very closely follows the chassis roll on all of them. :-)
half, Jun 06 2005

       It's bad to need third-party joke assistance, isn't it?
bristolz, Jun 06 2005

       It's a dirty job, but somebody had to do it.   

       I always get your jokes. Somehow, I doubt that that makes you feel better. Now that I think about it, it disturbs me a little.
half, Jun 06 2005

       angel, thanks for the link. No, I didn't know that. Is it a fable that the design brief was to have a car that could drive over a ploughed field without breaking a box of eggs inside? I remember having a 'race' (if you could call it that) down a dual carriageway in my Cortina 1600E, against a 2CV. I just couldn't let my semi-collectible Ford be overtaken by something named 'Two-horsepower'.
Ling, Jun 06 2005

       When I said "I assume most of us know how well those things handle", I also assumed that most of us would realise that they didn't. The fable is true.
I also had a Mk II Cortina (1968), but only a 1300. It was not quite the worst car I've owned, that honour going to a 1971 Victor 1600, complete with drum brakes all round.
angel, Jun 06 2005

       //No, I didn't know that// - the 2CV had interconnecting front and rear sway bars.
//No, I didn't know that// - the 2CV handled well.

       I just wanted to be clear :)
Ling, Jun 07 2005

       The point of anti-roll bars is to reduce the roll of the vehicle when cornering without having to have springs that are stupidly stiff, which would give a harsher ride. The reason we want to reduce roll (apart from sea-sickness!) is that this also rolls the wheels/tyres in relation to the road (despite many clever suspention geometries being used), therefore reducing the useful contact area of the tyre and reducing grip/traction and tyre lifespan.   

       Pitch in a car does no cause so much of a problem (unless you have a geometry which varies camber with compression). Therefore, this is only going to be a useful invention on the track, but I can see a lot of low ground clearance formulas/classes finding more reliable 'ground effect' downforce during braking and acceleration.
Skrewloose, Sep 22 2008

       I'm not sure how this whole thing got so nasty but I guess i could throw in $.02. The reason why suspensions are rarely diagonally or horizontally linked is because it would cause a dramatic destabilization in traction. Conventional swaybars (and some axles etc.) reduce roll by loading the suspension on the opposite side of the car. In general this is good but it does reduce the traction of the inside wheel. Now if we apply the same notion to movements front to rear, we find that this would have disastrous results: On hard breaking or acceleration the front and rear wheels would tend to lift, loosing traction and thus stability. If anything designers want to minimize this tendency.
WcW, Sep 23 2008


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