I haven't assembled all the parts yet, but the caster in late TR4's is not
adjustable, it's built into the upright. Caster is nice because it
provides some self-stabilizing of the front wheels, in the same manner as
furniture casters (hence the name, probably) the offset axle on a caster
wheel puts the center of force ahead of the contact patch of the wheel,
and thereby drags the wheel straight.
For any wheel, when the axis of steering input intersects the midpoint of
the contact patch (zero caster) there is no self correction applied to the
wheel. This makes steering forces light, but also makes it vague since
there is no force pushing back against steering input. Of course if you
dial in a lot of caster it gets hard to turn the wheel at speed.
I come from the motorcycle world, where caster and trail are critical
elements of making a motorcycle handle. It's a lot easier to see how this
works when you look at the front fork of a bike. Road bikes, that need
stable steering, tend to have their forks raked out substantially. This
puts the centerline of the steering axis well ahead of the contact patch.
This distance is called trail and is actually the critical dimension in
determining how much self-centering force is applied though it's rarely
talked about in car suspension. The angle of the steering axis is called
the caster. Trail is more precise because if you decrease wheel size with
the same caster angle you decrease trail and the self-centering force.
At extreme amounts of caster there is a "flop over" effect that you can
see when someone parks a chopper or when the spindle gets bent on a
shopping cart. The caster itself does not produce the stability, and in
fact positive caster always works against the self steering force. But
increasing caster increases trail, which does induce self-center forces as
soon as the vehicle is moving.
-----Original Message-----
From: Robert Dardano [mailto:19to1tr6@attbi.com]
Sent: Tuesday, March 25, 2003 7:51 PM
To: Susan and Jack Brooks; Ken Gano; fot@autox.team.net
Subject: Re: BJ's
Could some one explain the adjustability in the trunion of the TR-4 Is the
3 deg. built in.? and if its built in how does it get adjusted ? And at
the risk of tipping my rookie hand A very fast national MG driver once
told me caster is a great thing because it tells you what the car is
doing. Anyone
care to jump in thanks rob
----- Original Message -----
From: "Susan and Jack Brooks" <tr3a@att.net>
To: "Ken Gano" <triumphs@consolidated.net>; <fot@autox.team.net>
Sent: Wednesday, March 12, 2003 11:25 AM
Subject: RE: BJ's
> Ken,
>
> The question was one of adding adjustability. By using the TR4-6
> upper
arms,
> the TR4 trunion and the aforementioned Jag ball joint, you gain castor
> adjustability. The ball joint in narrower (front to rear) than the TR
piece, so
> judicious use of shims will allow you to "move" the BJ forward or back
> to
suit
> your needs.
>
> Jack Brooks
>
> >-----Original Message-----
> >From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net]On
> >Behalf Of Ken Gano
> >Sent: Wednesday, March 12, 2003 12:57 AM
> >To: Susan and Jack Brooks; fot@autox.team.net
> >Subject: RE: BJ's
> >
> >
> >I have the TR4-TR6 upper arms and the TR4 trunnions on a TR3A. It's
> >not adjustable, but it does give a fixed three degrees of castor.
> >Now, what
was
> >the original question? :)
> >
> >Ken Gano
> >
> >
> >-----Original Message-----
> >From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net]On
> >Behalf
Of
> >Susan and Jack Brooks
> >Sent: Tuesday, March 11, 2003 8:11 PM
> >To: fot@autox.team.net
> >Subject: RE: BJ's
> >
> >Nick,
> >
> >I found all the details. It was the series III, not the II. They
> >are as
> >follows:
> >
> >Use the late TR4-TR6 upper arms, with a Jaguar Series III ball joint
> >to provide adjustable caster & camber. You must use with the late
> >TR4 trunnion that has 3
> >degrees of caster built in to it.
> >
> >Again, I have no personal experience with this arrangement.
> >
> >Please let me know if anyone confirms this arrangement, off list.
> >
> >Thanks,
> >
> >Jack
> >
> >***************
> >
> >Nick,
> >
> >I believe what you are looking for is the Jaguar Series II upper ball
joint.
> >
> >The setup I am aware of is for providing adjustable caster to a TR3.
This
> >involved the use of TR4 upper arms (so it'll work for a TR4 also) and
> >a Jaguar Series II upper ball joint. The joint is narrower than the
> >TR ball and needed
> >to be shimmed front or back to move the pivot point accordingly.
> >
> >I don't recall where I became aware of this combination of parts, but
since
> >I
> >have not yet executed it myself, so you may be well advised to wait
> >for a confirmation from the list, before buying the ball joints.
> >Sorry I
couldn't
> >be
> >more definitive, but until I do it myself, it's hear-say.
> >
> >Can anyone confirm the Jaguar Series II upper ball joint is what Nick
> >is looking for?
> >
> >Later,
> >
> >Jack Brooks
> >
> >>-----Original Message-----
> >>From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net]On
> >>Behalf Of Malaboge@aol.com
> >>Sent: Tuesday, March 11, 2003 9:47 AM
> >>To: fot@autox.team.net
> >>Subject: BJ's
> >>
> >>
> >>Fellow Modifiers-
> >>
> >>A while back someone mentioned some thinner upper ball joints from
> >>(I
> >>think) a Jag of some sort that would fit the big TR cars. Now that I
> >>have carved up a set of trunions to give more castor, I need these
> >>thinner joints in order to move the upright!
> >>
> >>Never one to let it rest...
> >> Nick in Nor Cal
> >>
> >>Why is it that if the label says take two tablets, its always shake
> >>none, shake one, shake one, shake three...BUT if its take one its
> >>always shake none, shake none, shake two!
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