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Is a rear antiroll bar neccesary?
(32 posts, started )
Is a rear antiroll bar neccesary?
Is an anti roll bar really necessary to make a car handle well? On a car without a rear anti roll bar, wouldn't increasing the (bump?) damping of the rear suspension have the same effect as having a rear anti roll bar?
#2 - amp88
Trying to use another part of the rear suspension setup to compensate for the loss of a rear anti roll bar would compromise that part of the suspension. Using roll bars gives you a a dedicated piece of equipment to try and control the roll leaving you the dampers to control the ride over bumps/kerbs etc. If roll bars weren't necessary they wouldn't have been developed and they wouldn't still be employed in most (all?) major car racing championships.
Dampers only work on transients, so it can't do the same job.

Stiffening the rear springs to give the required roll rate would work, but then you'd end up with excess ride rate...

The best thing to do, if an ARB is required, is to fit one.
rac handles like its rear wheels have marshmallows fitted on them instead of tyres solely due to the lack of anti roll bar.
they do... they're called tyres.

some play is required but use the bar itself - too fiddly of a job to try and sort the loss of one, then they're are 99 other headaches to sort out...
Quote from tristancliffe :Stiffening the rear springs to give the required roll rate would work, but then you'd end up with excess ride rate...

So, stiffening the rear springs would reduce roll in the rear, but also affect the longitudinal load transfer (possibly adversely)? Where does the longitudinal load transfer come into handling, anyway? There's alot of talk about lateral load transfer in general, but not much discussion with respect to longitudinal load transfer.
It's not so much longitudinal load transfer, but the wheel frequencies. Stiffen the springs to act as the roll control and you end up with a car that will be too stiff to absorb the bumps, and will tend to pitch around and 'porpoise'.

In an ideal world you want to decouple ride and roll, so that you can have a nice stiff car in roll, but with the suppleness to ride well (or, if you so desire, to have very solid ride but allow the car to roll if you think that will be of benefit).
#8 - Joris
the antiroll bar absorbs the roll but as a trade in the load will shift more to the outer wheels.

Stiffening the front arb causes the front end to absorb more of the roll which means the rear wheels will be loaded more evenly but the outer front wheel to be loaded even more compared to the inside one. This will make the car understeer. and the outer front tire will heat/wear more.

Stiffening the rear will make the rear end absorb more of the roll and keep the front more evenly loaded at the trade of rear end grip.

I use this a lot to balance a car in my LFS setups.
I think we know how and why an ARB works. This thread is about whether a rear ARB can be duplicated by 'clever' use of damping or ride springing (or some other alternative suggestion as yet unmade).

The basis of anti-roll bars controlling load transfer distribution are known and understood by even the most untechnical racer.
Quote from tristancliffe :The basis of anti-roll bars controlling load transfer distribution are known and understood by even the most untechnical racer.

I thought so too, that's why I was so dissapointed no one brought it up allready.
you could always alter the suspension geometry to put the roll centre right into the cog
no wait...


it would still tilt to the side, no?
Quote from george_tsiros :no wait...


it would still tilt to the side, no?

By "it would still tilt to the side" do you mean "it would still roll?" I think the answer would be no, because the forces are acting upon the center of gravity, and the roll center is the point that the center of gravity rotates around. If the two points are equal, then there shouldn't be any body roll, or that's how it would seem to me.

I think that's why many people will install springs that are shorter, because it lowers the center of gravity thus shortening the distance between it and the roll center. Since torque is force x radius, and the force is the same, but the radius is decreased, then the torque acting upon the center of gravity is decreased.
The trouble is that the roll center isn't a static thing - it moves. Up and down, left and right, by several meters in some cases.

Lowering a car by fitting shorter springs does lower the CoG, but it doesn't necessarily do any favours to the roll centre control (or camber control), and thus very often is a bad thing to do that will make the car slower.
whats interesting is why the question is so specific, i.e. rear antirollbar rather than just antiroll bars.

possibly we're looking at a specific case in question, certainly on a front wheel drive car fitted with twisting beam suspension the fact that the beam has to twist to allow independant rear wheel movement means it acts as an antirolbar, manufacturers would specify the thickness of the U section to achieve the stiffness they required. so any additional bar can be avoided purely by stiffening up the beam. usually by the simple process of converting the U section into a box section by welding plates across the open side. however at best this is an inexact way of stiffening it and as far as i know was only used as way round competition regs that prohibited additional of non standard antiroll bars but did allow for the standard suspension components to be strengthened.

going way off topic but following in the spirit of "strengthening" suspension components, a certain engine tuner, best known for his work on mini's, campaigned another make of car in the british touring car championship in the '70s and was repeatedly crticised by his competitors etc for retaining the standard fuel tank location under the boot floor which mean he had to carry extra weight to protect it, rather than follow convention and mount it in the boot. what no one realised at the time was that his fuel tank protective structure had the effect of forming a smooth surface from the rear axle to the lip of the lower rear valence which gave him a lot less drag than the others who had a gap before the rear valence then presented the airflow with a flat vertical surface
must've meant centimeters.
Nope, some cars - particularly F1 cars in the 80s and 90s that had instananeous roll centers that moved about 3 or 4 meters to the side in corners, by design. Quite why, I don't know though!!!
how does a laterally moving roll centre effect the car anway? reducing roll by having the tyre loads push up against the roll?
Yes, I'd like an explanation of the effects of a non laterally central roll centre.
Who knows - if I did, I'd be earning megabucks.

Most cars have a non-central instantaneous roll centre though. When one wheel is in bump and one in droop then it's pretty unlikely that the lines cross on the centreline of the vehicle.
Quote from Bob Smith :Yes, I'd like an explanation of the effects of a non laterally central roll centre.

Actually I just remembered having a discussion about a related topic with Todd several years back.
One of the many topics (we veered a bit well actually a lot from the original discussion) was the rather unusual (not so much by F1 09 standards) front suspension of the BF1 which does have a very high roll centre.

The effect of this is a force that pushes the car upwards under lateral tyre loads. I still find the whole way of thinking about roll centres in that particular example confusing and thinking of the way the upwards angle of both wishbones naturally converts any lateral load into an upwards force seems much simpler to me.

Anyway my point is that the height of the roll centre doesnt only factor into how much a car rolls under lateral loads but also into how much the suspension is compressed or extended under these loads.

It is quite obvious that differing vertical tyre loads will cause a car to roll and it seems logical that the lateral location of the roll centre will govern how the suspension and body reacts to these loads.
So with a well aligned suspension that has the roll centre right between the tyres driving across a sleeping policeman will lift the car while an out of whack suspension should effect some body roll when hitting the speedbump dead on.
Isn't the answer to the OPs question dependent on the type of rear suspension system in use?

Surely a rear beam suspension system would have less need of a discrete ARB given that the beam itself will do a similar thing to a greater/lesser degree??
If you really want good handling, buy coilovers
Quote from Scrabby :If you really want good handling, buy coilovers

Is a new sign of irony? Please explain how and why coilovers will make good handling. (except from giving an extra line of text on the front door)

Is a rear antiroll bar neccesary?
(32 posts, started )