Rear sway bar on IRS

[bones]

Is a rear sway bar contraindicated on an IRS car? I was told it won't let the IRS work properly. Any comments?

[Glenn]

Big improvement. I've had one on my 74 since 1980.

[gcorrado]

I was told it won't let the IRS work properly. Any comments?

yeah, i have a comment... BOOOOOOOGUS! forgive me if i rant, but i've gotta squash the myth here and now.

rear sway bars work perfectly well on semi trailing arm rear suspension (what we call IRS). all manner of semi trailing arm cars came with rear sway bars straight from german factories - porsche 944 early 911s and just about everything BMW for example.

using a rear sway bar can greatly improve the handling of an IRS bug. it is recommended that you upgrade the front sway bar at the same time, or you may change the handling character of the car in a way you may be VERY unhappy with.

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understand what a sway bar does:

what a sway bar does is increase roll stiffness without increasing compression stiffness. what the means is that when your car is moving up and down with unevenness in the road, or in braking or acceleration, the sway bar has no effect. it's like it's not even there, so you sill get your nice smooth ride. it is only when the body tries to roll in a corner that the roll bar comes into play transfering weight to the outer wheel and resisting the body's desire to roll.

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understand the confusion of others:

part of the reason some people are confused is because of this term "IRS", which is supposed to stand for Independent Rear Suspension. this is a misleading name to say the least. what VW calls IRS is normally called semi trailing arm suspension. semi trailing arm suspension is only one type of independent suspension. other types of independent suspension included full trailing arm (what standard beetles have up front), mcpherson strut (what superbeetles have up front), double wishbone (what formula 1 cars have on all four corners), and even lowly old swing axle.

that's right. swing axle rear suspension is a type of indepenedent rear suspension. admittedly it is absolutely the worst type of independent rear suspension imaginable, but it still is indepenedent rear suspension. VW recognized the swing axles were awful for handling (with a little help from ralph nader). so they abandonded swing axle independent rear suspension and upgraded to semi trailing arm indepenedent rear suspension. this was a big upgrade though still not the best design from a performance standpoint. the only trouble is they marketed it as IRS, confusing the petuties out of a lot of people.

okay so both swing axle (stinky) and semi trailing arm (not bad) are independent. but where does this idea that sway bars interfere with independent suspension come from?

well it is true that the addition of a roll bar makes the suspension no longer literally perfectly independent - as in the motion of one side of the suspension can generate a movement on the other side. but perfectly independent suspension action is not really the goal of suspension design.

the advent of independent suspension was a reaction to and an improvement upon solid axle designs - where the two wheels are actually rigidly linked. solid axle have all sorts of problems and are rarely used anymore - and then only when handling has taken a back seat to some other design goal like toughness.

so yes and sway bar takes some of the "indepenedence" out of the VW IRS design, but it does so in quite a desireable way. your body will roll less, you'll feel more in control, and you car's steering be crisper and more responsive.

[Glenn]

I was told it won't let the IRS work properly. Any comments?

yeah, i have a comment... BOOOOOOOGUS! forgive me if i rant, but i've gotta squash the myth here and now.

Yeah... what he said.

All i know is my butt stays put better with a saw bar than without.

BTW... the correct term is Anti Roll Bars.

[bones]

Thanks for the info!! It's just what I thought. I have a Ghia - lowered with avis adjusters and dropped spindles along with 195-50-16 soft compound tires, narrowed trailing arms, discs all around, berg 5 with a good HP motor. I figure with the anti-roll bars front and rear the car should handle nicely. I'll be posting pics when the car is finished.