God forbid I should offer myself as a suspension expert (all I know is how to
get filthy working on them). But, I do recall a discussion long ago on the
list about rear sway bars. My recollection is that they are effective on
smooth,
virtually bump-free race tracks because they reduce roll and "fix" the rear
suspension in place, leaving all the compliance up to the tires, more or less.
That said, someone who had mounted one said that it was really un-streetable
because it also transmits every bump and bang right into the frame, and then
into your spine. I would think also that it would put a lot of stress on the
rear trunnions, which are none too sturdy to begin with.
Tom Burke
In a message dated 2/13/2006 10:01:27 AM Eastern Standard Time,
r.gosling@penspen.com writes:
> Doc, Larry, and all -
>
> Yes, the swing spring was implemented to minimise the inside wheel tuck.
> But how did it achieve this? Think about the difference in the systems
> - the fixed spring resists both wheels travelling in the same direction
> (thus supporting the car), and also resists one wheel travelling up and
> one travelling down (thus resisting roll). The swing-spring resists
> both wheels travelling up, but offers minimal resistance to one wheel
> travelling up and one travelling down, so little roll resistance.
>
> Wheel tuck occurs when the inside wheel is unloaded in hard cornering.
> By giving the rear suspension very little roll resistance, the weight at
> the rear of the car must be supported almost equally by both rear wheels
> - if there was more vertical force on one wheel than the other, the
> imbalance in force would just rotate the spring about its pivot on the
> diff until the forces were equal (if the lowest leaf weren't fixed, i.e.
> it was a fully swinging spring, you could be certain that the contact
> force between each rear wheel and the road would be pretty much
> identical).
>
> If you fit an anti-roll bar, what will that do? Well, on hard
> cornering, the car will roll (a bit at least), the outside wheel will
> move up in the wheel-well. The anti-roll bar exists to resist the
> wheels being at different heights (relative to the chassis), so it will
> push down on the outside wheel and up on the inside wheel. Hmm, pushing
> up on the inside wheel, reducing it's contact force with the ground -
> that's what caused the wheel tuck in the first place, wasn't it? That's
> what we're trying to avoid, right?
>
> OK, that may have got a bit convoluted. A somewhat simpler way of
> envisaging it - with a swing-spring, if one wheel goes up, the spring
> swings and pushes the other wheel down. An anti-roll bar works by, if
> one wheel goes up, it pushes the other wheel up. An anti-roll bar
> directly counter-acts what the swing-spring is trying to do.
>
> Any attempt to add roll stiffness to the rear of a swing-spring car will
> reduce the effectiveness of the swing-spring at preventing wheel tuck.
>
> I will read attentively and open-mindedly to any reasoned explanation of
> why I am wrong! Like I said, I'm not a suspension expert by any means,
> but I should temper that with being a professional mechanical engineer,
> who has thought a lot and read some about how the suspension on my
> little (and sadly long-departed) Spitfire works.
>
>
> Richard Gosling
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