How do anti roll bars work?
Discussion
I can't draw diagrams so I will try and explain.
As the car leans over to the outside of the bend the wishbone/trailing arm is pushed up (the strut is compressed).
As this is linked to the other wishbone/trailing arm on the other side by the anti-roll bar, the bar tries to lift the opposite wishbone/trailing arm up so therefor the car pulls down on that side. Got it?
I'm sure somebody will be along in a minute to explain it better than me.
If you can't feel a broken anti-roll bar link then you are not driving hard enough.;)
As the car leans over to the outside of the bend the wishbone/trailing arm is pushed up (the strut is compressed).
As this is linked to the other wishbone/trailing arm on the other side by the anti-roll bar, the bar tries to lift the opposite wishbone/trailing arm up so therefor the car pulls down on that side. Got it?
I'm sure somebody will be along in a minute to explain it better than me.
If you can't feel a broken anti-roll bar link then you are not driving hard enough.;)
garycat said:
Considering my drop link looks like this and I haven't really noticed much difference in the handling....
What is it supposed to do?
RX8? Or do other cars have similarly sWhat is it supposed to do?
t ARB drop links? To be honest, I noticed the improvement when I replaced mine rather than detecting a dramatic downturn in handling when they broke (whenever that was...)
M.
anti roll bars work by opposing the suspension from travelling in opposing directions (ie up one side down the other), thus stopping the car from rolling under lateral load.
On a modern car they are purely there as a way of fine tuning the handling balance, and contrary to popular belief, they reduce mechanical grip, not increase it. So by it being rendered useless by a knackered drop link all you are doing is making one end of the car roll more so than the other.
some people honestly think they are as important as the spring or shock so are confused as to how little difference they make when a drop link is knackered.
On a modern car they are purely there as a way of fine tuning the handling balance, and contrary to popular belief, they reduce mechanical grip, not increase it. So by it being rendered useless by a knackered drop link all you are doing is making one end of the car roll more so than the other.
some people honestly think they are as important as the spring or shock so are confused as to how little difference they make when a drop link is knackered.
deveng said:
On a modern car they are purely there as a way of fine tuning the handling balance, and contrary to popular belief, they reduce mechanical grip, not increase it. So by it being rendered useless by a knackered drop link all you are doing is making one end of the car roll more so than the other.
Well... and changing the diagonal weight transfer characteristics, hence changing the cornering balance of the car.As deveng said, they actually reduce mechanical grip; therefore a front ARB reduces front end grip (by diagonally transferring more load onto the outside front tyre, making it work harder) - which tends to increase understeer.
So if its your front ARB droplink that's knackered, if you drove the car harder you'd find the handling balance biased more toward oversteer and rear-end breakway.
Unless you drive like a complete f
kwit, the chances are that at this time of year, on public roads, you shouldn't be pushing hard enough to notice too much change in the handling balance, though.doogz said:
Here's a slightly off topic question for you, since you do seem to know your stuff.
On the back of a Saxo/Ax/106/306 etc, there are 2 torsion bars, one for each side.
And they are marked, so you know which one is for which side, as apparently if you fit them to the wrong side, they're more or less useless, as they are made in such a way that they resist torsion much better in one direction of rotation, than the other. Some sort of tempering technique when they're made i guess.
Any idea why? springs are equally springs in both directions, why would you want torsion bars to be different?
There's a slight amount of plastic deformation as they settle in - some people call it 'set' - at the factory the bars are pre-stressed one way at elevated temperatures so that it occurs in the direction they will be used in, which means that the ride height will stay consistant and not drop as they settle in. High quality springs go through a similar process.On the back of a Saxo/Ax/106/306 etc, there are 2 torsion bars, one for each side.
And they are marked, so you know which one is for which side, as apparently if you fit them to the wrong side, they're more or less useless, as they are made in such a way that they resist torsion much better in one direction of rotation, than the other. Some sort of tempering technique when they're made i guess.
Any idea why? springs are equally springs in both directions, why would you want torsion bars to be different?
Hence you don't want to put them in the other way.
doogz said:
So, does it act as a torsion bar, or are you just selectively picking up on little bits of text again, so you can be right.
Yes it does act as a torsion bar, that's exactly what it is.I don't need to selectively pick up on little bits of text to be right when you are so damned good at being wrong.
doogz said:
Fair comment, as well as supporting the weight of the car though, a torsion bar acts as a spring, where an anti-roll bar doesn't. Guess it depends on your definition of torsion bar. Or really, whether you apply a description to the definition.
Here's a slightly off topic question for you, since you do seem to know your stuff.
On the back of a Saxo/Ax/106/306 etc, there are 2 torsion bars, one for each side.
And they are marked, so you know which one is for which side, as apparently if you fit them to the wrong side, they're more or less useless, as they are made in such a way that they resist torsion much better in one direction of rotation, than the other. Some sort of tempering technique when they're made i guess.
Any idea why? springs are equally springs in both directions, why would you want torsion bars to be different?
If I'm not mistaken they are made out of spring steel, and it would presumably still oscillate if it weren't for the car's primary damping, but yeah it's there because it's flexible not because it's bouncy! Here's a slightly off topic question for you, since you do seem to know your stuff.
On the back of a Saxo/Ax/106/306 etc, there are 2 torsion bars, one for each side.
And they are marked, so you know which one is for which side, as apparently if you fit them to the wrong side, they're more or less useless, as they are made in such a way that they resist torsion much better in one direction of rotation, than the other. Some sort of tempering technique when they're made i guess.
Any idea why? springs are equally springs in both directions, why would you want torsion bars to be different?
On the topic of the Saxo/Ax/106/306, assuming that there's no assymetrical bracketry or some such then... I have no idea. Nor does anyone in my office
Although we are the Powertrain department, so I'll have to ask Ride and Handling!
ETA - Answered for me by PhillipM, and quite an interesting answer at that!
Edited by The Wookie on Wednesday 16th February 13:45
Niether is telling someone that it's not a spring or torsion bar (which is entirely what it is, it wouldn't work otherwise, you'd be back to dependent suspension) and then jumping on the first person to correct you. Especially when you've jumped on other users to 'correct' them...
Edited by PhillipM on Wednesday 16th February 13:47
Well said PhillipM.
As I see it an Anti-Roll bar simply transfers load across the car, from the 'loaded' side to the unloaded side. This has the effect of adjusting the spring rates dynamically:
On the loaded side, the ARB acts to increase the total spring rate (coil spring rate is constant+ the additional spring rate of twisting the ARB).
On the unloaded side, the spring rate is reduced - the ARB torsion acts against the coil spring to reduce the total spring rate. This has the additional benefit in softening the unweighted side of the car, so that bumps hit mid bend on the less loaded wheel (think Gambon) will have less of an effect on the overall stability of the car.
As I see it an Anti-Roll bar simply transfers load across the car, from the 'loaded' side to the unloaded side. This has the effect of adjusting the spring rates dynamically:
On the loaded side, the ARB acts to increase the total spring rate (coil spring rate is constant+ the additional spring rate of twisting the ARB).
On the unloaded side, the spring rate is reduced - the ARB torsion acts against the coil spring to reduce the total spring rate. This has the additional benefit in softening the unweighted side of the car, so that bumps hit mid bend on the less loaded wheel (think Gambon) will have less of an effect on the overall stability of the car.
WeirdNeville said:
This has the additional benefit in softening the unweighted side of the car, so that bumps hit mid bend on the less loaded wheel (think Gambon) will have less of an effect on the overall stability of the car.
Kick me if I'm wrong, but I thought assuming a torsion bar with linear spring rate would result in the wheel rate remaining the same, regardless of roll. There is more load transfer to the outside wheel and thus away from the inside wheel, but the stiffness would be the same, meaning that the car is likely to be more susceptible to mid corner bumps than one without a roll bar.
Again, completely thinking out loud so correct me if I'm wrong.
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