X sway bar idea

[shaundrake]

Wouldn't it be nice to have 2 sway bars that connect the rear wheels diagonally across the car to the front wheels? That way in a turn, you could take traction off the inside rear tire and transfer it to the outside front tire, and from the inside front tire to the outside rear tire?

I know the bar would have some trouble clearing the exhaust and leaving you enough clearance beneath the car. Also there would have to be some kind of non interference bracket where the two bars intersect at the center of the car. But anything is possible, right?

[Jim]

G'day,

Thats a great question and an idea that has occupied the minds of many chassis designers for a long time. Long enough in fact to have spawned a number of solutions over the years.

Unfortunately most to date have been either too expensive or complicated for road cars while race versions are generally banned as soon as they become viable - its called active suspension :-)

The function of the "diagonal swaybars" you mention are much easier to mimic with hydraulics or hydropneumatics. Imagine an active shockabsorber/spring unit on each corner of the vehicle linked via hydraulic line to a single pump. Diagonal weight transfer is just one of the functions but imagine how good it would be if it was possible to allow a zero spring rate for any individual wheel when it hit a bump while providing theoretical infinite rate for roll?

;)

Cheers
Jim

Whiteline

[Jakub]

Indeed such a layout, if designed well, delivers a desirable non-rigid inter-connection between wheels. The pitch and roll suspension modes would in this case be stiffened while the heave (bounce) and warp mode would be unaltered.

This for street cars is a very practical approach, in terms of handling characteristics, yet in terms of packaging it is quite a design problem which has left this idea relatively unexplored. Hydraulic connections instead of mechanical would lighten the design for packaging, although the system would still be complex in nature.

Jakub Zawada B.E. (Mech)
jakub01@whiteline.com.au

Go flat out with Whiteline Automotive

[shaundrake]

I'm going to spend a lot of time beneath my car and see if I can work out a design that a custom sway bar shop would be willing to tackle. I've been thinking about this for a long time. I will have to come up with at least two mounting points per bar, a way to attach the end links, and something to prevent the two bars from interfering in the center.

I haven't even begun to address the issue of bar length and diameter. We always speak of bars in terms of diameter, but length is obviously very important since adjustable bars only adjust the length. Can you recommend a starting point?

[Jakub]

Its quite difficult as even for a ballpark figure you need rough locations of pitch and roll axis locations. However you can get an estimate from the original anti-roll bars on the hatch. Assuming the X bars will be twice as long as the orignal ARB's, the diameter needs to be approx. 19% larger to retain the same roll stiffness (for the same moment arm or blade length).

Jakub Zawada B.E. (Mech)
jakub@whiteline.com.au

Go flat out with Whiteline Automotive

[halz]

http://www.zerorollsuspension.com/

...well, its not the same idea as connecting wheels of different axles together, but it at least has a similar name...! 'Link-X'; just some food for thought



It would not be very practical to have 'bars' span the length of the vehicle from axle to axle.. once the length and thickness of the bar is determined, I'm sure they would add a considerable weight..

Never mind the packaging... how would the car react if a front wheel hit a rumble strip?

[Jakub]

Similar name, although pretty different, it uses a X shaped setup with the upper and lower control arm to generate a roll center which is fairly high, this reduces the amount of body roll present.

Although the downsides include large jacking forces which push the sprung mass upwards when cornering, and some large camber changes and scrub which could be a problem.

Its true there is a weight issue with spanning bars along the length of the chassis (instead of across like ARB's), although you are gaining anti-pitch in the suspension, and you are improving the warp mode in the suspension (softer warp mode than with normal ARB's).

The softer warp mode (front suspension rolls opposite to that of the rear suspension) generally gives much better road holding and sprung mass control. So if the front wheel hit a rumble strip it would certainly handle better with the "X bar" setup than the standard ARB setup!

As Jim initially said the best setup would be if the spring rate for one wheel bump would be zero!

Jakub Zawada B.E. (Mech)
jakub@whiteline.com.au

Go flat out with Whiteline Automotive

[shaundrake]

I'm sold already! Stop teasing me.

I'd be willing to pay $1000 USD.

[shaundrake]

So you use a large diameter, hollow bar because the length of the bar is so long. Weight is an issue but I'm still not convinced that it doesn't pay for itself.

The arms on the ends of the swaybar have to be parallel to the lower control arms, so that the up and down movement of the arms rotate the bar. Any bends in the bar have to be able to rotate under the chassis for the full arc of wheel travel w/out contacting the chassis.

The chassis mounting have to be custom made plates welded to the underbody, with enough ground clearance, and with enough reinforcement not to tear out. Also, some kind of mount that prevents the two bars from rubbing together at the center of the car has to be fabricated, with the biggest problem being that there isn't a convenient mounting place for the bracket at that point under the car. And ground clearance again, being an issue. But perhaps the bars can simply be shaped so that they don't interfere.

I can reuse my normal swaybar end links unfortunately by removing my normal swaybars. I'm not sure whether this will benefit my handling but it works for experimenting purposes and later I can redesign the end links.

Anyone want to chime in? Am I missing something fundamental to this type of project? What is the length vs diameter stiffness equation? For instance, X meter in length = 1mm stiffness.

[Jakub]

Hi Shaundrake,

Using the hollow bars is a good way of dropping some weight, it may be a little hard to manufacture and will need a little more attention to design around stressed areas.

In terms of the X arrangment I always assumed that the original anti-roll bars were left out, and replaced by two "X" bars.

Im not quite sure on your question with the length and stiffness, although length and bar torsional stiffness is a 1 to 1 relationship ship, that is a bar twice as long will be half as stiff. So you can base the new bars on the original bars, and from the previous reply I gave a value of 19% larger bar diameter for a double length bar to retain the original bar rates in roll.

The reason its not double the diameter is that the rate and diameter relationship is very nonlinear, and double stiffness is around 19% increase in solid diameter. Hope this is all clear.

Regards
Jakub Zawada B.E. (Mech)
jakub@whiteline.com.au

Go flat out with Whiteline Automotive