Nick
Your theories are good however they do not explain why bump steer is still
experienced in a lowered 1600 that uses rose joints (no bushes involved).
This problem is still solved through the use of strut spacers
Regards
Brad HALLETT
http://www.powerup.com.au/~bhallett
Proudly Endorsing:
...DATRATS...
http://203.33.35.34
Datsun Dedicated
For Nissan Motorsport Components
Professional Budget Priced competition equipment
Contact Errol SMITH
email: [EMAIL PROTECTED]
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED]]On Behalf Of abrahamk
Sent: Friday, September 29, 2000 8:07 PM
To: [EMAIL PROTECTED]
Subject: Re: Strut spacers (long)
Errol,
This is the crux of the matter, it all depends on how the toe-control rod
bush behaves in reality as opposed to theory.
If it behaves as a 'pure' spherical joint and the joint is in line with the
inner transverse arm bush axis and this line is parallel with the centre
line of the car and horizontal then,
it should be, in effect, the same as a one-piece A-arm.
I think that this is a good approximation for standard ride heights.
Yeah????
When you lower the vehicle excessively the toe control rod will not be
perpendicular to its mounting bracket and the bush will be compressed
unevenly at the static ride height.
So when you start to roll into a normal turn the bush has already been
compressed the same as if you had just gone over a speed-jump/hump at
100kph. There is too much resistance from the bush to the toe-control rod
swinging in an arc, the 'pure' spherical joint theory breaks down - hey
presto - instant toe-out, and it gets more severe then more you lower the
car and the more you compress the suspension :(.
I have seen some Yank sites on the 1600/p510 and they drill holes in their
urethane toe-control bushes to give extra compliance to counter-act the
bump-steer effect on the lowered car. (They didn't give an understandable
reason why they drilled the holes but I suspect this is why).
Drilling holes in the bush solves one problem - a little bit - but still
leaves the problem of increased scrub because the effective transverse arm
(a line from the centre of the ball-joint to the centre of the transverse
arm bush axis) is not horizontal (parallel to the ground). Drilling holes in
the bush reduces the axial stiffness of the bush so you get bump-steer
anyway - may as well just tie it in with a bit of rope!
Your strut spacers correct the geometry of the lowered car and because of
this they,
1. Minimise scrub and
2. Minimise bumpsteer especially if urethane (hard) bushes are used and/or
the car is lowered heaps.
I think I've answered my own question!!!!
Doh!
Regards,
Nick
----- Original Message -----
From: Errol Smith <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Friday, September 29, 2000 8:50 AM
Subject: Re: Strut spacers
> Nick,
> Correct me if I am wrong, but wouldn't the lower control arm ball joint be
> describing a different length arc to the tie rod when the arm is above
the
> horizontal position?
> Cheers
> Feral Errol
>
> ----------
> From: abrahamk <[EMAIL PROTECTED]>
> To: [EMAIL PROTECTED]
> Subject: Re: Strut spacers
> Date: Thursday, September 28, 2000 11:49
>
> Errol,
> I don't think that the toe control rods/castor control affect the steering
> characteristics of the car at all (or not much).
> If Datsun got their suspension design right (they certainly kept it for
> long
> enough!) then the centre of the toe control rod bush and the centre of the
> transverse arm bush should describe a line that is parallel to the
> centre-line of the car and horizontal, and that also intersects the
> steering
> arm joint, i.e a virtual A-arm with no inherent bumpsteer.
> If this line is not parallel with the centre line of the car, for
anti-dive
> etc.. this would certainly cause bumpsteer.
> But I bet you've seen Ford Escorts and other 'gun' cars that have woeful
> suspension geometry, i.e sway-bar acts as toe control rod etc.. They don't
> seem to spear off the road and wrap themselves around trees and power
> poles - much.
> Therefore the speed limit should not apply for any modified Datsun - since
> the handling and braking must be so good by comparison ;).
> I have had a quick look/measure under my car with a bit of string and a
> steel ruler (not very accurate +/- 5mm say), but the geometrical design
> seems pretty good - at stock ride heights :).
> Regards,
> Nick.
>
> ----- Original Message -----
> From: Errol Smith <[EMAIL PROTECTED]>
> To: <[EMAIL PROTECTED]>
> Sent: Thursday, September 28, 2000 8:26 PM
> Subject: Re: Strut spacers
>
>
> > Nick,
> > I call them strut spacers!
> > Your post is correct. Normally the arms are angled below horizontal so
> that
> > on bump the control arm length increases relative to the pivot
horizontal
> > plane and then starts to shorten relative to the pivot when over
> > horizontal.
> >
> > The fact that the arms normally pass over the centre point of the plane
> > means that they experience minimal length change (relative to th4
> > horizontal plane) during bump. This means they maintain their lengths
> > relative to the tie rods.
> >
> > If the control arm angles are horizontal or above then the relative
> length
> > to the tie rod will decrease during bump. This causes the wheel to turn
> in
> > towards the centre of the vehicle. This is bump steer!
> > Cheers
> > Feral Errol
> >
> >
> > ----------
> > From: abrahamk <[EMAIL PROTECTED]>
> > To: [EMAIL PROTECTED]
> > Subject: Bump Steer Spacers
> > Date: Thursday, September 28, 2000 6:58
> >
> > Errol et. al.
> > I have alluded to this in previous posts but I haven't been put straight
> > (Yet!);
> > Why are those spacers called 'bump-steer' spacers.
> > By my reckoning they should be called 'scrub' spacers.
> > A lot of people have talked about the front transverse arms being angled
> > down-to-the-outside, in reality however, what is important is the
> > hypothetical plane between the centre of the outside ball-joint and the
> > transverse arm mounting bush. This should be horizontal, i.e parallel to
> > the ground, presumably this is what the spacers achieve on a car that
has
> > been lowered.
> > As you all know, scrub is the change in track, i.e the distance between
> the
> > front (or rear) wheels' contact patch.
> > And the transverse arms move in arcs, obviously, so therefore the track
> > will vary in pitch and roll - and it will vary least when the 'plane' is
> > horizontal.
> >
> > Wadderurekon?
> > Nick
> >
> >
> >
>
>
>
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