tom111

Hi,

Can you please elaborate on the functioning of the “Sway bar”, I mean what exactly does it do??? And what is the recommendation, should I leave it on or remove it? on my FG MT I have a rear sway bar & on my MCD MT I have rear & front sway bars, I mainly drive these cars on off road fields & in off road tracks.

Thanks,
Tom

Foxy

The sway-bar, or anti-roll bar, does pretty much what it says on the tin. It connects the two lower arms, preventing them from articulating separately. What this means is that the chassis does not 'sway or 'roll', the car corners flat.

The basic rule for anti-roll bars, is that the stiffer they are, the more grip they provide at the OPPOSITE end of the car, sacrificing the grip at the end they are placed. Therefore, if you have a car which understeers, you increase rear roll bar stiffness to reduce rear grip and increase front grip. Vice versa for an oversteering car.

All of this sounds great, right? But, on an off road car, they are nearly worthless. What do all off road cars have? Long travel independent suspension, so that the suspension can all articulate independently. Adding a stiff anti roll bar, immediately denies the suspension this ability. Anti-roll bars are only useful on smooth off road tracks and are a total liability on rough ground, ruining the articulation of the suspension.

Hope that covers it for you. The FG rear anti roll bar is particularly stiff and ruinous to the handling of the MTs, it should come off if all you do is bash around.

Ballistic Lunacy

Best guide to sway bars out there: http://www.rc411.com/pages/howto.php?howto=22&page=1

Basically they lower the Centre of Gravity throughout cornering by limited binding of the left and right hand sides of the front or back suspension arms. As one suspension arm of the car is pushed up during a corner, the sway-bar pulls the other side up as well which lowers the car through the corner, how much is dependant on how think a bar your running and how heavy your suspension springs are. Suspension geometry will also be optimised as they prevent chassis roll which throws camber during a hard corner (hence the proper term anti-roll bar), this keeps more of the tyre in contact with the ground and optimises grip.

Something to keep in mind is that you MUST run lighter springs when you add a sway-bar, if you just continue to run the same springs (assuming you've found the ideal ones for a given track/terrain) then your spring rates act like they are harder. Many people make the mistake of throwing a sway-bar on and expecting the car to just perform better. Sway bars are a tuning option and one that has to be tuned in by you.

Suggest you read the guide though, will explain their function more completely they any of us can off the top of our heads.

wan6176

A sway bar is usually a torsion spring that resists body roll motions. It is usually constructed out of a U-shaped piece of steel that connects to the body at two points, and at the left and right sides of the suspension. If the left and right wheels move together, the bar just rotates about its mounting points and does not bend. If the wheels move relative to each other, the bar is subjected to torsion and forced to twist.
The bar resists the torsion through its stiffness. The stiffness of an anti-roll bar is based on the fourth power of its radius, the stiffness of the material, the inverse of the length of the lever arms (i.e., the shorter the lever arm, the stiffer the bar), the geometry of the mounting points, and the rigidity of the bar's mounting points. Some anti-roll bars, particularly those intended for use in auto racing, are adjustable, allowing their stiffness to be altered by increasing or reducing the length of the lever arms. This permits the roll stiffness to be tuned for different situations without replacing the entire bar. The stiffer the bar, the more force required to move the left and right wheels relative to each other. This increases the amount of force required to make the body roll.
In a turn, the sprung mass of the vehicle's body produces a lateral force at the center of mass (CG), proportional to lateral acceleration. Because the CG is usually not on the roll axis, the lateral force creates a moment about the roll axis that tends to roll the body. (The roll axis is a line that joins the front and rear roll centers (SAEJ670e)). The moment is called the roll couple.
Roll couple is resisted by the suspension roll stiffness, which is a function of the spring rate of the vehicle's springs and of the anti-roll bars, if any. The use of anti-roll bars allows designers to reduce roll without making the suspension's springs stiffer in the vertical plane, which allows improved body control with less compromise of ride quality.
One effect of body (frame) lean, for typical suspension geometry, is positive camber of the wheels on the outside of the turn and negative on the inside, which reduces their cornering grip (especially with cross ply tires).
Anti-roll bars provide two main functions. The first function is the reduction of body lean. The reduction of body lean is dependent on the total roll stiffness of the vehicle. Increasing the total roll stiffness of a vehicle does not change the steady state total load (weight) transfer from the inside wheels to the outside wheels, it only reduces body lean. The total lateral load transfer is determined by the CG height and track width.
The other function of anti-roll bars is to tune the high g-force and limit understeer behavior of the vehicle. The limit understeer behavior is tuned by changing the proportion of the total roll stiffness that comes from the front and rear axles. Increasing the proportion of roll stiffness at the front will increase the proportion of the total weight transfer that the front axle reacts and decrease the proportion that the rear axle reacts. This will cause the outer front wheel to run at a higher slip angle, and the outer rear wheel to run at a lower slip angle, which is an understeer effect. Increasing the proportion of roll stiffness at the rear axle will have the opposite effect and decrease understeer.

Hope i dun bored you.

46u

My Feedback: (3)

I run them on both my 1/8 race off road buggies and my 1/5 5B SS off road racer.

Foxy

Bajas are very different to FG MTs. The stock rear anti-roll bar on the FGs is like a coat hanger.

Lars from Norway

1/5th clothes that is

SAVAGEJIM

I notriced that too; the FG anti-sway bars are VERY stiff, and I have teken them off my FG MTs since they do not give like they are supposed to and lift the wheels to the inside ot the turning radius instead of offering some give to fight roll-over but still allow the inner wheels to provide some traction.

As for finding softer FG anti-sway bars, I have yet to find some. I guess I will have to try to fashion my own using some milder steel bars and experimenting with those. (I just have to find the right bars of the right diameters made of spring steel, otherwise I am afraid they will permanently distort instead of spring back.)

Ballistic Lunacy

Just get some Piano/Music wire from your LHS/Craft shop.

tom111

Thanks guys for all the explanations, I guess that for my purposes & the off road tracks that I am running my cars on I will need to remove the sway bars, I also noticed that the FG shocks are very stiff & probably I will need to replace also the oil there to a softer one, this might be part of the stiffness that I face now, the FG MT has 8 shock instead of 4 shocks which also increases the stiffness of this car, in general the off road behavior that I am now facing is like a refrigerator on wheels…

Foxy

Remove rear sway bars, put 800 (euro weight) silicone in all shocks. Enjoy...

tom111

What is the stock oil that comes in the FG shocks? I guess it is stiffer than 800???

Foxy

2000

tom111

Wow! No wonder they are so stiff! Will get the 800… thanks!

Foxy

When I took my shocks apart for the first time, I realised how poorly assembled they were. The plastic pistons still had flash material ON THE SIDES OF THEM, where they contact the shock body. I trimmed them very carefully, and they are now better, but it is now my highest priority to get the alloy pistons with the rubber o-rings, I have absolutely no doubt, that this will at last give me the smooth shock action I have been seeking without me spending a fortune on competition shocks. Perhaps you might want to consider this too.

wan6176

foxy regarding the silicone oil on shock wats the maximum size do they have..? i intend to get the thickess if possible for my home made car 1/4 scale using baja rear shock.

reddog6625

hello

Well my sway bars are meade of bicycle rim spokes and they are holding up well... they r felxible hardened steel (different colours) and easy to fit them in i bought some quality ones like dt swiss rim spokes........

Ballistic Lunacy

Wonder how many of these home brew sway-bars made from materials other then spring steel are still straight when they're taken off, cause if their not and they end up getting twisted, they bork your suspension when their on.

reddog6625

WELL the spokes do they job. First it was like you told lunacy, bending and not going back. But once i hawe theese quality ones they allright

SAVAGEJIM

The Piano wire sounds like a great idea. When I was in the South, the Hobby Towns all had piano wire of various diameters, but they were used primarily as cables or linkages for airplanes and helis. I hope I can find the right wire of the right diameters to my MTs. I guess ebven if they are smaller, I can rig up bracing spacers out of spare RC plastic I have laying around everywhere.

As for bike spoke wires, that too is another option I have not considered (or even thought of). I will hit the bike shops and buy some and experiment with those. Well, I will first have to do some experiments to find out just at what forces and deflections they can take before they go into their plastic phases. I can care less about ultimate failure points; for purposes of sway bars, once they enter the plastic phase, that IS the point of failure.