Rxmfn7

iTrader: (4)

Id like to get a discussion going on the overall purpose of the front and rear swaybars, from a technical perspective (what they actually do), to what people will notice in handling from installing a thicker or larger diameter bar. Also, what are the advantages to a solid bar over a hollow one? Also should there be any correlation to spring/dampener stiffness and the thickness of a swaybar?

I have a good bit of experience running alot of different spring/strut, and fully adjustable coilover setups, but swaybars were always a bit of a mystery as to what I will actually feel with different types, and I thought others may have the same questions.

jgrewe

iTrader: (1)

Sway bars take some of the load when the car tries to lean in a turn. 'Part" is the key, so yes there is a relationship with the springs. You can go with stiff springs and soft bars and get the same total roll stiffness as soft springs and stiff bars. The trick is to figure out what will work best on the surface you will run on.

A hollow bar will give you most of the stiffness of a solid bar of the same diameter, its usually cheaper and easier to make a solid bar. Its also heavier...

As for sizing bars, its up to you and everything else you have on the car, lots of variables. First they give you roll stiffness which can help keep the tires in a camber range you want, then they will also help tune the handling. Simple terms, the "effectively" stiffer end will break away first. There are equations for figurin gout how stiff a bar is, dia is only one variable and its not the most important one. Lever arm length will give you more change for small adustments.

Sandro

iTrader: (1)

Sway bars are clever equal arms levers connecting the right and left springs to make them work together during cornering. With a huge swaybar, you can almost double the spring rate at the loaded corner, since the lever will rigidly push against the spring at the unloaded corner. Both springs now work together against the weight transfered to the loaded corner.
With swaybars, you can make the suspensions stiffen during cornering while keeping them soft when you go straight.

Also, since both springs get compressed during cornering, sway bar cause less body roll.

Lesser sway bar equates to lower "combined" spring rates and more body roll. This is because a less rigid swaybar get twisted and the spring at the unloaded corner get compressed less.

Since swaybars connect both sides of the suspensions and make them work together, too much sway bar defeats though the benefits of independent suspensions. For this reason, big (or any) swaybars are not desirable in the rear, where you want to have maximum compliance to put your power down.

Swaybars are also used to fine tune the speed of weight transfer between front and rear (together with springs and shocks) during side by side transitions (corner entry or exit) and induce more or less understeer/oversteer. E.g., everything else equal, more swaybar in the front cause quicker side by side weight transfer in the front, with consequent larger slip angles, therefore understeer. Note though that swaybars (or other suspension components) play no role in steady state cornering after suspensions have settled and all weight has transferred to the outside.

Finally, the only advantage of using solid bars is they cost less. Torsion stiffness is a function of D^4. The outer parts of a bar contribute the most while the inner contribution is negligible.

maxcooper

The sway bars do affect the angle of the wheel versus the ground (camber) in steady-state (by influencing the resting position of the suspension), which in turn affects the amount of grip available.

-Max

phoenix7

now. If I have the adjustable endlinks how would I go about adjusting the sways to reduce understeer and improve handling?

mods:

KYB AGXs all around
eibach pros
RB sways and links
front and rear strut tower bars.
removed PS
225's on all corners

maxcooper

To reduce understeer, remove one of the end links from the front bar.

If you just have adjustable-length end links, those are for eliminating pre-load. They are not intended to change the handling balance of the car. (Even though they can change the balance when turning left-vs-right, the net effect on overall balance is essentially zero.)

Or do you mean that your bar has multiple holes to connect the end links to? To reduce understeer, make the front bar softer by connecting the links to the holes that are further away from the bar. This gives the links more leverage to twist the bar, thus making it act softer.

But, I suspect you mean adjustable-length end links.

-Max

Sandro

iTrader: (1)

That is correct. The sway bar keeps pushing up the spring at the unloaded side. The "combined" spring rate at the loaded side is higher and the car stays flatter. This minimizes change in camber.

Sandro

iTrader: (1)

What kind of understeer? Corner entry, steady corner or corner exit?

Usually, corner entry understeer is generally due to excessive entry speed; steady state understeer is generally due to any or a combination of front weight bias or height or track (narrower in the front than the rear) - nothing you can do about it with sway bars; corner exit understeer is a tough one - try by slowing down weight transfer to the rear by softening rear shock compression and/or taking it easy on gas throttle, but could just be worn tires.

As Max said, adjustable end links (like Mazdatrix) do not play any role.

DamonB

No they are not; shocks do that.

Springs and swaybars have absolutely no effect on how quickly the weight transfers across the car.

Also incorrect. In any steady state condition the springs and bars are THE dominant factors.

And NO suspension components play a role during steady state? Than what does? Divine Intervention?

This is exactly the type of problem adjustable swaybars were designed to help solve.


From the Suspension and Handling Links sticky:

Everything about Sway Bars by Grassroots Motorsports

Sandro

iTrader: (1)

I respectfully disagree – although I have to partially elaborate on my previous statements on steady-state cornering. Please note the following.

Weight/load transfer is caused by acceleration (in any direction).

Load transfer of the sprung weight is transmitted to the tire patches through the suspensions.

Suspension stiffness determines the speed at which load is transferred to the tires (literally – load is transferred quicker in a go-kart with no springs than in your grandma Cadillac).

Suspension stiffness is a function of springs, sway bars, shocks, and the tires themselves (and chassis flex).

Understeer/oversteer is determined by differences in slip angles (F and R) due to difference in tires loads F and R or changes in friction coefficients when tires get overloaded (saturation).

Amount of tire load after weight has fully been transferred trough the suspensions (i.e. springs/swaybars compressed to the point where the react with a force equal to the weight transferred) – steady state cornering – is mainly a function of track width and car weight distribution (height of CG and of mass virtually concentrated in the CG) – assuming the four tires are equal. Differences in these three combined parameters between F and R determine understeer/oversteer. E.g. if you assume equal track width F and R, same CG height F and R, but a weight biased to the front the car will understeer. There is no way you can correct this basic unbalance by tuning your sway bars or springs. Since the springs are now fully compressed and in equilibrium you could actually change on the fly springs with a solid rod and wouldn’t notice any difference.

Now, having said that, real life tarmac is not perfectly smooth and suspension get solicited and moves continuously during steady state cornering. In the meantime, weight transfer keeps getting induced because of angular acceleration during cornering. Since suspensions keep moving, and small weight transfers occur continuously, loads will be transferred quicker at the end with stiffer springs/sway bar with a resulting small amount of understeer/oversteer even if the car is balanced correctly otherwise (by the right combination of track width, weight distribution and tires).

- Sandro

DamonB

True. Unfortunately suspension stiffness has absolutely nothing to do with weight transfer.

The equation for lateral load transfer is:

Lateral Load transfer= (G*CG height)/track width

Where
G = cornering G
CG = center of gravity

The equation for front/rear load transfer is:

Load transfer= (G*CG height)/wheelbase

Where
G = acceleration or braking G
CG = center of gravity

You'll notice these equations don't include springs, sway bars, shocks, tires or chassis flex because those things have no effect whatsoever on the amount of weight transfer.

There is an awful lot of misunderstanding in your post above. I'd suggest:

Racecar Vehicle Dynamics

The Physics of Racing by Brian Beckman Weight Transfer

Everything about Sway Bars by Grassroots Motorsports

Dynamic Load Transfer

Sandro

iTrader: (1)

Y

Sandro

iTrader: (1)

You have to distinguish between the weight/load transfer once it has happened/completed - what I referred to as steady-state cornering condition - with the dynamic on how the weight/load is transfered to the tires.

The formulas you are referring to deal with a final steady-state condition. I was referring exactly to this condition/formulas when I initially stated that the springs/sway bar play no role in determining (or correcting) understeer/oversteer in steady-state cornering once the springs/sway bar have settled.

However, the dynamic/transition to that end state is a different story. That is what I called the "speed" at which weight/load is transferred. And this is where spring rates, sway bars, shocks (as well as tire pressure) play their role. They all contribute (although with some different mechanisms) and can be tuned to control such "speed" and therefore induce understeer/oversteer at will. Again, think at the difference between a go-kart (no springs) and a soft underdampened old Cadillac. Or, more appropriately, think at you car with OE springs and compare it with an autox SM2 with 900lb/in springs. Which one do you think get tires loaded first? Or think at your preferred corner entry while trail braking and your rear Penske rebound cranked up to their stiffest click. How nicely/quickly get your front tires loaded while your rear rotates nicely around that cone.

As for the referenced books, thank you. I have happened to have read most of them (as well as others) many years ago.

jgrewe

iTrader: (1)

The easy way to end this is that it is not how much, its how fast, the weight transfers. That is where the balance of the car comes from.

phoenix7

yes, you are right. I have the adjustable-length end links. I'mma go lounge around in the stickies and FAQs to learn the terms.
You are right. The times i've understeered have been cuz I came in a tad too fast.


thanks for the info and links, I love equations. I have a lot of research to do and I will eventually have some questions on what stumps me. I might need to pick some brains in here.

I finally got my project running right and I can autocross it. The grassroot article is great. Thanks for a new info source.


so I read that I should install the adjustable endlinks while the wheels are on the ground. What does adjusting the link either way DO? These are the RB links. I got a good deal on the RB kit. I installed the sways and did nocite a difference in handling. It seemed to ride on rails ( even more than before: TII sways) but I wasn't sure about the actual use of the links so I haven't installed them yet.

maxcooper

If you put a really stiff bar on the front, that will increase the weight transfer at the front of the car (and reduce the rear weight transfer by an equal amount), which will reduce the grip in front, and result in a balance that is more prone to understeer in steady-state cornering. That's a balance change caused by changing how much weight is transferred in the front versus the rear.

-Max

Sandro

iTrader: (1)

I see there is still much confusion here.

Jgrewe summarized it correctly "The easy way to end this is that it is not how much, its how fast, the weight transfers. That is where the balance of the car comes from."

Sway bars (as well as any other suspension components) do not have anything to do with the amount weight/load transfer [see formula in DamianB post # 11] but greatly influence how fast the load transfers to the tires.

Differences in suspension stiffness between F and R determine which end gets loaded first - therefore differences in slip angle or faster tire saturation (loss of grip).

However, as I also indicated in my post #10, since even during steady-state cornering the suspensions keep moving because pushed by the tarmac irregularities, a stiffer front suspension will give a tendency to understeer. But this only because there are continuous accelerations at play, and the tire loading happens faster at the stiffer end.

Eggie

I disagree.

An anti-roll bar twists when a car leans in a corner. The outside wheel moves up in bump, pushing up on that end of the bar. Vice versa on the other side. What does the bar do? It tries to return to its original shape and pushes right back! So the ARB pushes down on the outside tire (increasing load) and pulls up on the inside tire (decreasing load). IOW, the bar transfers load from the inside tire to the outside tire. We can easily visualize how these forces fight body roll, as the bar attempts to lever the car upright.

We seem to have all agreed that total weight transfer is not related to the suspension setup, just track width and so on. So if a stiff front ARB upgrade handles X pounds of the total transfer, that much less occurs in the rear, giving the same total. Reread Max Cooper's post above.

Now, what do we know about tires? The important factor here is that the grip a tire provides diminishes with load. When X pounds transfer from inside tire to outside tire, the outside's grip increases less than the inside's decreases, serving to decrease overall grip. This explains why lower cars are faster: they transfer less weight, giving more grip.

Put this stuff together, and we see that an ARB's load transfer decreases tire grip at that end of the car. Therefore a stiff front bar leads to less front traction (i.e. understeer), even during steady-state cornering. Suspension movement and speed of transfer are not needed for this to occur.

Sandro

iTrader: (1)

It's still a matter related to the speed of load transfer, not the amount, as the suspension resettle.

A way to figure this is to imagine a steady-stade cornering on an ideally perfectly flat surface, such that there are not accelerations induced by bumps.

In that case, once the suspensions have settled, they are out of equations. The only parameters that matter are weight, weight distibutions, and track width. As you rightly pointed out, outside's grip increases less than inside's decrease. Therefore, in order to maximize overall grip, it is desirable to minimize weight/load transfer by having low center of gravity and a wide track. Now, still in our ideal example, if the weight distribution is perfectly 50/50 and so are the CG heights (you can virtualize two CG Front and Rear), same track F and R (and of course same tires), the load on the two outside tires will be equal F and R, the loads on the two inside tires will be equal F and R (but less than the ousides). Car is perfectly neutral. Now change the equation (e.g. front biased weight distribution) to have more weight/load transfer in the F, less in the R, and the car will understeer. Well, suspensions do not play any role in this (other than through second order effects the way they influence CG through body roll). Whether or not you have swaybars or even springs for that matter.

Eggie

Sandro, do you agree that an ARB transfers load from the inside tire to the outside tire during cornering? If not, please explain how the ARB reduces body roll. What forces are applied and where?

Sandro

iTrader: (1)

No, it doesn't. Load does transfer from the inside to the outside whether a car has sway bars, quadruple adjustable shocks, any kind of springs or nothing of the above.

Sway bar reduces body roll because it increases the wheel rate at the outside suspension by "using" the inside spring to resist the load that goes to the outside tire. That causes the outside spring to compress less. In addition, the inside spring gets compressed by the bar and lowers that side of the car as well. Hence, less body roll.

Best to figure this out is to consider how an ideal infinitely stiff sway bar would work (imagining nothing else flexes, chassis, bar mounts, control arm bushings, etc.. and that the only "flexible" things we have are the springs).

When the load starts getting transfered trhough the outside spring, the spring compresses and pushes up the arm of the sway bar connected to the outside suspension lower control arm. Since this "ideal" sway bar cannot twist (infinitely rigid), the sway bar arm connected to the inside suspension lower control arm will move up by the same amount and pushes the inside spring. This will continue until the springs get compressed by the exact amount needed to generate enough force to counteract the weight transfered to the outside.

E.g. let's assume we have 300 lb/in springs, weight transfered to the outside wheel upon cornering is 1300 lb, while the the initial weight resting on the outside wheel is 700 lb (car going straight at steady speed) - 600 lb difference. With no sway bar, outside spring has to compress an additional 2 inches [I know there is a motion ratio to consider also but let's assume it is 1.0] to develop the required 600 lb and takes say 2 sec to do this, which becomes the time it takes to transfer the full 600 lb additional load to the outside tire. Now, let's install our super-stiff bar. Since the two front springs now work together, it takes only 1 inch (and 1 sec) to absorb the additional 600 lb load and transmit it completely to the outside tire. Not only that, but there is zero body roll (and the CG gets also 1 inch lower).

The example above serves also to demistify I hope another myth about how much understeer a big front sway bar could make. Use of sway bar needs to be evaluated together with the springs being used. Even the biggest sway bar you can think of would at the most double the wheel rate. With stock or moderately soft stock springs, the benefit of using a huge sway bar is very noticeable. The front wheels get loaded quicker and the car stays flatter. Much crisper turn in and responsiveness. However, bigger sway bar in the rear brings significant downsides as you want to keep the rear suspensions independent to assure compliance with the pavement to be able to properly put down power (also, you may be unconfortable controlling a car with a higher stiffeness, as load transfers would be faster).

Sandro

iTrader: (1)

Sorry I realized I made a mistake in the example above, with the infinitely stiff bar.

The springs would actually not move at all. With a 600 lb weight transfer, with no bar the outside spring would compress 2 inches, and the inside spring would extend 2 inches (600 lb less weight on the outside wheel). If the bar cannot twist (by definition since it is infinitely stiff) the springs cannot longer move independently. Since the total weight on the two wheels has not changed, both springs will have to stay at the same height. This means the load transfer will be super fast, like if there were no springs. Real world sway bars have a limited stiffness though, will twist, the outside wheel will compress some, the inside spring will extend some.

Sorry for the confusion. All other conclusions stay.

phoenix7

i'm so lost. I guess I have a lot to read (i stayed uo till 3 AM last night reading)

It also looks like I can't race this year. Getting my project running has slowly drained my funds and I don't have enough for SCCA driver's school

maxcooper

I think we all agree that ARBs do not change the total weight transfer during steady state.

However, ARBs do change the amount of weight transfered at each end of the car, which will change the handling balance, including during steady state conditions. And it isn't just because road irregularities keep the suspension from truly reaching steady state. I don't think we have unanimous agreement on this yet, but it is my position that it is true.

Say you have a car with a track width (front and rear) of 57.3", which means that the wheels will travel 0.5" for each degree of body roll. The car will roll 4 degrees per G of lateral acceleration, as determined by the mass, roll axis, CG height, and the total roll stiffness. The effective wheel rate (including stiffness from both the springs and from the ARBs) at both ends of the car is 150 lbs/in. In a 1G steady-state turn, we'll get 4 degrees of body roll, and the wheels will travel 0.5x4= 2", x150 lbs/in wheel rate = 300 lbs of weight transfer at each end of the car (600 lbs total).

Now imagine that we change the ARBs in such a way that we keep the total roll stiffness equal to what it was before, but the front effective wheel rate becomes 175 lbs/in (stiffer ARB) and the rear effective wheel rate becomes 125 lbs/in (softer ARB). In the same 1G turn, the car still rolls 4 degrees, since we didn't change anything that would affect the total amount of body roll. Now it yields 2" x 175 = 350 lbs of weight transfer in front, and 2" x 125 = 250 lbs of weight transfer in the rear (total is still 600). We just changed the weight transfer in the front versus the rear just by changing the ARBs.

This will affect the balance of the car in steady state for the reasons described above, wrt to tire grip versus load.

-Max

jgrewe

iTrader: (1)

Or, simple version of above, the end of the car that resists the roll more will break away first.

There are a ton of variables even in that statement but that is what will happen if the suspension is identical front and rear and the center of gravity is right in the middle of the wheelbase. Oh and you are leaning without steering... and your tires are the same size... and same track width... must resist... long posts....aarrrgghh