quote:
Originally posted by ron norman:
1
It has the frame brace from an after market vendor already.
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I'd like to have the seam welding done,
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alignment, per that fancy digital expensive alignment tool. The caster is maxed out already
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and the bump steer kit is installed, but as per previous bump steer tech articles, some bump steer remains.
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I'd like those new front a-arms as an upgrade. That sounds like it would be the biggest help, with a reasonable price tag.
Thanks again.[/B]
Ron
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In the last PI issue, I show where the flexing occur.
I am suspicious about the effect of seam welding. This is an old racers method of stiffening up a chassis, many times to stay within the rules, as a welded in roll cage is banned. I have newer seen any stiffness numbers from these actions, and I doubt it is has any considerable effect. We must understand that Chassis stiffness has the biggest influence on wedge-tensional loads, via the shock-springs control over vertical wheel movement.
3
In this story we may also notice the not so great value of a �fancy digital alignment board�. It didn�t help the problem. Twisting movements around the steering axis, affecting the steering wheel, is another story. This is due to power outside centre of the kingpin axis. Like scrub distance. I think Jack by misstake confused 8 and 7 inch Campagnolo wheel offset with scrub radius. Depending on ride height of the car the ground projection of KPI varies, as KPI has an angle. The higher the car the greater the track of the projection. But an average of 50,60 inches will do for an example. Standard front track width with 7 inch wheels is 57,48 inches. 57,45-50,60=6,88�. 6,88/2= 3,44 inches of scrub each side of the car. This makes 2,94� scrub with 8 inches wheels. But on the downside is a narrower Tw.
Caster keeps the wheel in straight ahead position, but creates a �trial� which is another type of �scrub� in another plane, as the projection line of the KPI comes in the front of the front wheel.
Caster is some sort of compensation for the 7 degree KPI of the Pantera, not to get positive camber in turns. Big scrub also affects trial when the wheel is in �turn� position, as the centre of the wheel is mowed forward, which is also compensated by caster. This is apart from steering wheel response. All these �scrub� distances will in one or another situation create
torsional power around KPI. And compensating one with another will move the problem elsewhere.
If we want to get rid of �steering response� we must minimise KPI angles and scrub to get all wheel loads in the KPI centre. But this takes huge rebuilds.
4
As I was thinking, the bump steer would not be the problem, and now it show as you already installed this without help. To get rid of bumpsteer completely, we got a BIG job. Forget it. Change the caster a bit and you are off again. Caster gives the steering arms another angle by rising or lowering the steering arm + ball joint in relation to
the rack.
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Front A-arm upgrade? There are nice A-arms to buy, but they don�t help the basic geometry problem. But some has better adjustability within factory geometry.
Goran Malmberg