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Author Topic: Geometry Castor adjustment, can it be done?  (Read 2344 times)

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wheels-inmotion

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Geometry Castor adjustment, can it be done?
« on: 30 December 2012, 11:29:41 »
Yes it can

Contrary to what Vauxhall and all the tyre shops say the Castor angle is adjustable on the Omega......

So what's the problem?
The Castor angle has many duties but the one that concerns us is toward directional stability..
1: Definitive explanation for those that need it can be found here> http://www.wheels-inmotion.co.uk/tech-longcastor.php
2: In a more simple format the front wheels are pulled by the off-set lower ball joints and the actual centre of the wheel, if the pull is uneven then the car will drift toward the lower value.

Historically over time the Omega geometry will evolve a low near-side-front Castor position, this combined with the road crown could induce a drift/ pull to the left.

To the point
Post 1994 the Omega's front subframe has six anchor points but these are not a surgical fit meaning if the anchor pick-up points are released the sub-frame can be moved and as a result change the Castor position.

How?
The sub-frame has four main 22mm bolts, two of these NSF/OSF are avalible through the wishbones, the other two just in front. Once released there are two 16mm bolts at the very front of the sub-frame, these also need to be released ( do not remove any bolts ) Once done a lever between the OSF sub-frame 22mm bolt can be used to jar the sub-frame back.

Moving the sub-frame back will increase the NSF Castor and reduce the OSF, in doing so the energy the Castor generates will be toward the road crown and belay any pull/ drift left.

I hope this helps.......



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GastronomicKleptomaniac

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Re: Geometry Castor adjustment, can it be done?
« Reply #1 on: 30 December 2012, 11:41:12 »
Handy to know - I'll probably be bringing mine to you sometime this year so it's something else to check... :y
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car5car

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Re: Geometry Castor adjustment, can it be done?
« Reply #2 on: 30 December 2012, 14:00:39 »
How about front camber?
rear camber and toe?
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Seth

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Re: Geometry Castor adjustment, can it be done?
« Reply #3 on: 30 December 2012, 16:08:48 »
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feeutfo

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Re: Geometry Castor adjustment, can it be done?
« Reply #4 on: 31 December 2012, 03:34:46 »
TheBoy, how does your caster angle compare over your two cars?
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wheels-inmotion

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Re: Geometry Castor adjustment, can it be done?
« Reply #5 on: 31 December 2012, 11:52:49 »
Quote from: car5car on 30 December 2012, 14:00:39
How about front camber?
rear camber and toe?

The link given explains the front camber issue. Point of the post is the Castor on most Omegas with a little age needs to be adjusted, you will be told "it's a fixed angle" i'm telling everyone it's not a fixed angle.
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TheBoy

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Re: Geometry Castor adjustment, can it be done?
« Reply #6 on: 31 December 2012, 12:01:02 »
Quote from: chrisgixer on 31 December 2012, 03:34:46
TheBoy, how does your caster angle compare over your two cars?
TBE:
Left: 5o47'
Right: 5o35'

Bullet:
Left: 5o10'
Right: 5o02'


@ wheels-inmotion - would the extra castor on TBE make it less stable? It had extra toe-out last time to try to make it more willing to go in a straight line.
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Kevin Wood

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Re: Geometry Castor adjustment, can it be done?
« Reply #7 on: 31 December 2012, 12:07:59 »
You sure it was toe-out?

I was always told that toe-in tends to improve directional stability at the expense of sharpness of the "turn in" which tends to improve with a little toe out but I'm no expert.

EDIT: then again, the Omega has the steering arms behind the wheel not in front, so maybe that matters? <head starts to hurt>
« Last Edit: 31 December 2012, 12:09:37 by Kevin Wood »
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feeutfo

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Re: Geometry Castor adjustment, can it be done?
« Reply #8 on: 31 December 2012, 12:13:34 »
It was toe in. Helps a little with tram lining, at the expense of some wear. But with these tyres, the extra wear is very welcome.
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feeutfo

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Re: Geometry Castor adjustment, can it be done?
« Reply #9 on: 31 December 2012, 12:18:54 »
Think of it in motorbike terms.

Compare the raked out steering angle of a chopper, to the much nearer vertical steering angle of a Gsxr sports bike.
The chopper is heavy steering and stable, but difficult to turn.
The Gsxr turns on a sixpence but is a nightmare in a straight line and will wobble off into the weeds at the first sign of a bump, unless it has a steering damper.(which is completely pointless)

However, if you fit Pirelli super corsers to the Gsxr it will become stable AND turn. But if you fit Dunlop 207 gp's the exact same bike it will be dangerous in a straight line and wobble into gravel trap at first site of a bump mid turn.

It's in the tyres I tell you. ;)
« Last Edit: 31 December 2012, 12:29:09 by chrisgixer »
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Rog

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Re: Geometry Castor adjustment, can it be done?
« Reply #10 on: 31 December 2012, 12:20:48 »
I didn't have a clue what all this was about. So I found this which helped me understand a bit

http://www.youtube.com/watch?v=Gh7gWJAvOvs
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05omegav6

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Re: Geometry Castor adjustment, can it be done?
« Reply #11 on: 31 December 2012, 15:57:24 »
Quote from: Kevin Wood on 31 December 2012, 12:07:59
You sure it was toe-out?

I was always told that toe-in tends to improve directional stability at the expense of sharpness of the "turn in" which tends to improve with a little toe out but I'm no expert.

EDIT: then again, the Omega has the steering arms behind the wheel not in front, so maybe that matters? <head starts to hurt>

Possibly simplistic, but rwd=toe in, wwd=toe out.

Rwd drive pushes the chassis through the front wheels forcing them to toe out. By setting the toe in this is countered.

Wwd torsion of the driveshafts, and therefore the wheel centres, pull the wheels in. Toe out counters this.
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GastronomicKleptomaniac

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Re: Geometry Castor adjustment, can it be done?
« Reply #12 on: 31 December 2012, 20:02:41 »
Quote from: ex taxi al on 31 December 2012, 15:57:24
Quote from: Kevin Wood on 31 December 2012, 12:07:59
You sure it was toe-out?

I was always told that toe-in tends to improve directional stability at the expense of sharpness of the "turn in" which tends to improve with a little toe out but I'm no expert.

EDIT: then again, the Omega has the steering arms behind the wheel not in front, so maybe that matters? <head starts to hurt>

Possibly simplistic, but rwd=toe in, wwd=toe out.

Rwd drive pushes the chassis through the front wheels forcing them to toe out. By setting the toe in this is countered.

Wwd torsion of the driveshafts, and therefore the wheel centres, pull the wheels in. Toe out counters this.

Every time I think I understand geometry, I learn a new bit to it that complicates it  8)
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Kevin Wood

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Re: Geometry Castor adjustment, can it be done?
« Reply #13 on: 01 January 2013, 01:05:08 »
Quote from: ex taxi al on 31 December 2012, 15:57:24
Quote from: Kevin Wood on 31 December 2012, 12:07:59
You sure it was toe-out?

I was always told that toe-in tends to improve directional stability at the expense of sharpness of the "turn in" which tends to improve with a little toe out but I'm no expert.

EDIT: then again, the Omega has the steering arms behind the wheel not in front, so maybe that matters? <head starts to hurt>

Possibly simplistic, but rwd=toe in, wwd=toe out.

Rwd drive pushes the chassis through the front wheels forcing them to toe out. By setting the toe in this is countered.

Wwd torsion of the driveshafts, and therefore the wheel centres, pull the wheels in. Toe out counters this.

Ahh. I should have said - I was talking about proper cars, not shopping trolleys. ;)

.. and thinking about how the wheels on shopping trolleys behave, I guess that's why they are called castors.
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2woody

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Re: Geometry Castor adjustment, can it be done?
« Reply #14 on: 01 January 2013, 23:29:21 »
don't forget the "trail" as well.

that difference in caster angle will make virtually no difference.
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