IRS discussion: was Re: Noise and vibrations.......

[juliemac57 at hotmail.com (Julie Macfarlane)]

This will take me about 6 re-reads, but good info Dan.



Julie Macfarlane
1981 MKI 2L 16v
Amsterdam NY





>From: "Dan Bubb" <jdbubb@ix.netcom.com>
>To: "Calimus" <calimus@techography.net>
>CC: scirocco-l@scirocco.org
>Subject: IRS discussion: was Re: Noise and vibrations.......
>Date: Thu, 18 Mar 2004 11:39:14 -0500
>
>First, I'd define independent suspension:
>If you can move one wheel/tire assembly from droop to bump without changing 
>the camber or toe of the
>wheel on the opposite side of the car, then that would be independant.
>I would define a beam axle as the two axles being contrained relative to 
>each other in six
>dimensions i.e they can't move relative to each other in 3 orthogonal 
>planes and they can't change
>angles relative to each other within those three planes.
>(I'm trying to make this easy, but it doesn't seem to be coming out that 
>way!)
>Anyway, the Scirocco rear suspension meets the definition above. If you 
>remove the spring/shock
>assembly from one side of the car then you can freely move that side up and 
>down and see that the
>other side is uneffected.
>If the Scirocco rear suspension was a beam axle then moving one side up and 
>down would change the
>camber of the other side. So, I guess the point is that just because a beam 
>is used in its
>construction doesn't mean it has the characteristics of a classic beam 
>axle.
>The Scirocco rear axle is really a simple version of a pure trailing arm 
>suspension. ( as opposed to
>a semi-trailing arm like the 924/944 Porsche)  It has no camber or toe 
>change from droop to bump. It
>is functionally no different from the twin beam concept that Julie 
>proposed. The neat part is that
>VW incorporated both sides into one unit. The "T" cross section is stiff in 
>bending in both a
>horizontal plane (to control toe during cornering loads) and in a vertical 
>plane (to control
>camber), but because of it's open cross section is relatively weak in 
>torsion. So, VW was able use a
>really wide base for the bushings to minimized toe change due to bushing 
>deflection (roll oversteer)
>and at the same time incorporate some roll stiffness into the structure. 
>It's a really neat design
>in its simplicity except for its complete lack of camber change to improve 
>cornering.
>Almost all suspensions have some sort of interconnection from side to side 
>in the form of a swaybar.
>That interconnection doesn't make the suspension not independant (at least 
>according to my
>definition).
>Anyway, if you're looking to replace the "T" beam with a bar or tube there 
>is a good chance you will
>increase roll resistance at the cost of a lot less stiffness to control toe 
>and camber deflection
>due to cornering and bump loads.
>There's lots more to say about how the position of the beam effects camber 
>change if anybody's
>interested.
>Hope all that was clear.
>Dan
>
>
>----- Original Message -----
>From: "Calimus" <calimus@techography.net>
>To: "David Utley" <mr.utility@highstream.net>
>Cc: "Dan Bubb" <jdbubb@ix.netcom.com>; <scirocco-l@scirocco.org>
>Sent: Wednesday, March 17, 2004 6:43 PM
>Subject: Re: Noise and vibrations on the steering.. Solve one, find 
>thereason for the other !
>
>
> > I knew this would happen, LOL.  I took the conversation off list, but if
> > you want to join in thats cool.  My viewpoint is that it's not IRS and I
> > kinda explained that a bit.  My basic idea is to replace the cross piece
> > of the rear beam with a torsion bar.  That would achieve IRS wihout
> > having to fab tons of new mounting points and all that happy stuff.
> > Just have to do some fabbing to the rear beam and bolt it back in the
> > same way it came out.
> >
> > William
> >
> > David Utley wrote:
> >
> > >Dan,
> > >  Now trust me, I am not trying to incite anything but friendly 
>discussion,
> > >but you knew someone would ask...  How is it that it is independent, 
>when it
> > >uses a beam?  Trucks (american) have an axle beam, and it is a rigid 
>rear
> > >suspension, what makes the A1 cars different?
> > >
> > >David Utley
> > >
> > >
> > >
> >
>
>
>
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