Increase Rear Roll Resistance By Increasing Stiffness Of The Beam

[JWB]

Fitting a rear sway bar is a common modification to increase the rear roll resistance which will increase front grip and hence reduce understeer.

But the rear wheels are already connected by the rear axle / beam. This must twist under cornering (otherwise fitting a rear sway bar would have no effect....) As the rear beam is a u channel and open on one side the stiffness of the beam can be increased by boxing it in or adding a lip along one edge.

The rear roll resistance could be tuned very easily by altering the amount of metal added to the beam.

One worry of adding sway bars that are non adjustable is you can not tune the balance easily, this method would let you tweak the roll stiffness to get a nuetral car.

Obviously care would need to be taken to ensure the additional metal and welding didnt introduce stress raisers to the beam and cause fatique cracks, or distort the beam.

Anybody tried this?

[stevet47]

I would think it would be better to just make swaybars of various diameters.

[Daemione]

I agree - a selection of sway bars would be MUCH less work than all that welding and grinding. And much more desirable to an autocross or track enthusiast, as cornering balance can be tuned wherever and whenever you want, with no more tools than a couple sockets, a jack, and some stands.

[secondspassed]

I've seen pics somewhere of someone who welded a metal rod inside of their torsion beam. And I believe (only seen in drawings, not in real life) there is a stock damper that is just kind of a block mounted somewhere around the middle of the torsion beam. Perhaps making a larger one could have some effect.

[tanukifit]

I was trying to find some early corollas had bolt on torsion stiffeners that bolted directly to the H beam. Jettas also have some too. Autos with h beam suspension and search for sway bars for those cars. Very interesting.....

[JWB]

Sway bars should be made from spring steel and heat treated. To get a selection of custom made bars in various diameters would not be cheap. However at the rear of a Fit this may not be required as the bar would not get close to its yield point.

I am thinking of a cheap way of stiffening up the rear, which to the casual observer is not obvious.

[tanukifit]

Sorry, finally got back to the computer. AutoSpeed - Rear Sway Bars: Improving FWD Handling
Here's the site I was looking for.http://www.g20.net/forum/showpost.ph...45&postcount=6 This one's kinda neat too.

[pilosopo]

Originally Posted by JWB

Fitting a rear sway bar is a common modification to increase the rear roll resistance which will increase front grip and hence reduce understeer.

But the rear wheels are already connected by the rear axle / beam. This must twist under cornering (otherwise fitting a rear sway bar would have no effect....) As the rear beam is a u channel and open on one side the stiffness of the beam can be increased by boxing it in or adding a lip along one edge.

The rear roll resistance could be tuned very easily by altering the amount of metal added to the beam.

One worry of adding sway bars that are non adjustable is you can not tune the balance easily, this method would let you tweak the roll stiffness to get a nuetral car.

Obviously care would need to be taken to ensure the additional metal and welding didnt introduce stress raisers to the beam and cause fatique cracks, or distort the beam.

Anybody tried this?

First off, what are your ultimate goals? Is it for a sporting daily driver? An all out track toy? etc.

The reason I ask is ultimately, increased roll resistance does not increase traction at the front, it reduces traction at the rear. That's why understeer goes away.

Though increased roll resistance is beneficial in strong transient maneuvers, it cannot be forgotten that a bar prevents suspension movement. By tying together the two sides of the suspension to the body of the car, a bar works by preventing the inside rear wheel from dropping down in a turn, not by limiting body movement. Because the car would prefer to have all wheels down, it essentially "leans" back towards the inside of the turn, to get the inside wheel down.

If you find you car too soft at the rear, or front for that matter, it's often more a byproduct off too soft spring rates. Though it may seem counterintuitive, many auto crossers (especially Miata guys) will go up in spring rate significantly and down in roll bar size and end up with better handling (dampers to match the strength of the spring are a given).

The reason is, the springs are strong enough to reduce and mitigate the roll of the car. The smaller bar allows more independent movement between the two sides of the car. The bar is then only there to fine tune body motions, not really handling. Though the spring rates may be significantly stiffer, the car often ends up as compliant or more compliant than before because impacts felt on one side are no longer channeled through the chassis to the other side by a large bar.

Personally, if I could, I'd like to go with stiffer spring rates (I'm looking at getting Swift Springs), keep the stock rear bar, and then step down to something slightly smaller in the front to increase traction and compliance there, and shift the handling balance towards neutral