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-   -   Roll centres and sway bars (https://www.rctech.net/forum/electric-road/52397-roll-centres-sway-bars.html)

ratter 10-10-2004 12:18 AM

Roll centres and sway bars
Just learning all this techo stuff and keep coming up with more questions.
I understand what the roll center is, what raising and lowering it does, but if we want our cars to roll in the corners to get traction, why do we have sway bars?


Speedie 10-10-2004 12:24 AM

We dont always want more traction. The bars are used for two things one it to prevent traction rolling on very high bite tracks and the other is a tuning option . A sway bar on the front adds more rear body roll by holding the front even and letting the roll roll more to the back wheels. the same if its on the rear. I rarely use a swaybar accept for rubber tired applications on carpet.

ratter 10-10-2004 12:29 AM

So am I correct to assume that a Sway bar is only used for either an incorrect roll centre adjustment or just to fine tune the roll centre?

Speedie 10-10-2004 02:08 AM

A sway bar doesnt affect the roll center at all that is all in the geometry of the suspension. A swaybar limits the amount of roll you get. A swaybar is a spring that connects the left and right side of the suspension and transfers some of the roll force from the outside to the inside wheel, based on the thickness of the bar. Its sort of the effect of a stiffer spring but with a different feel to it.

ratter 10-10-2004 02:33 AM

I do undertsand how a sway bar works, but if the roll centre was set correctly, it wouldn't need a sway bar, is that correct?

Dragonfire 10-10-2004 05:19 AM

Originally posted by ratter
I do undertsand how a sway bar works, but if the roll centrer was set correctly, it wouldn't need a sway bar, is that correct?
Yes and no.. it really depends on how you like your car to feel. I find better side-to-side transition is possible with a lower rollcenter and swaybar than running a higher rollcenter without a swaybar.

The best thing about swaybars though is the added stability you get. I have never been able to match that stability/grip combination with high rollcenters.

Graphitedust 10-10-2004 08:50 AM

Perfect timing...
Man.....we were just talking about this last night!

I have found that very few people have a sound understanding about sway bars, including myself......ask 10 people, get 10 different answers.

Here's my question:

Is the center portion of a sway bar, the part that attaches to the car chassis, suposed to be firmly fixed or is it suposed to float in its holder?

I asked some big time racers (names everyone would recognize) and got some really different answers.:nod:

Speedie 10-10-2004 10:06 AM

The bar definately should pivot in its holder but not to the point that there is slop in the mount. If the mount is not free to pivot the car will be really inconsistant. IT will not act right if there is too much play there either, it has to be able to pivot but not move.

mafiaracers 10-10-2004 04:25 PM

I can never remember....does a longer link=higher roll center? or is it the other way around?....I always forget.

dontfeelcold 10-10-2004 04:35 PM

a longer link will lower the rollcentre when the chassis rols

Scottrik 10-10-2004 05:20 PM

A swaybar/anti-roll bar held tight at the center is just a secondary spring. It is the ability to pivot at the center mounts that keeps it from adding spring load in strictly vertical input but add load when the suspension acting in roll.


Speedie 10-10-2004 05:22 PM

A swaybar will not affect the roll center of the car at all. That is all dictated by the angles of the control arms, and camber links.

ixlr8nz 10-10-2004 05:32 PM

speedie is right, the roll centre is determined by the camber link positions and has nothing to do with springs or rollbars.

A rollbar is used to control or limit body roll. For example you are in the turn and your inside tire starts loosing grip because of weight transfer to the outside wheel, you would stick a rollbar on.

The rollbar should be free to rotate in its mount and should not be bolted down tight where it cant move.


Disaster 10-10-2004 05:56 PM

Roll bars make independent suspensions less independent.
Roll (aka sway or anti-roll) bars make independent suspensions less independent. It ties the left and right independent suspensions together. This reduces the roll of the body....transfers some of the suspension load/travel to the other side. It will help keep the Cg lower in turns and reduce the left/right weight transfer when cornering.

Graphitedust 10-11-2004 08:33 AM

Sway bar attachment ...
Well, it sounds to me like a sway bar needs to be held in such a way :

1) that it can rotate up and down, so that it doesn't further stiffen the suspension (it can twist).

2) that it can twist or load from one end and transfer weight to the other end without bind.

3) that the center portion is restrained from moving up/down, forward/back, or sideways.

Maybe it is like a hub and axel.....the axel is allowed to rotate, but it is held in position by the bearings/hub!!! I think I may understand!!!! :nod: :D ;)

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