dom7
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| posted on 25/11/05 at 09:17 PM |
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problem of self centering
As some (a lot of ?) Indy owners I have a problem of self centering .
What is the good way to solve it ?
How people who fail SVA did to be OK for the retest ?
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greggors84
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| posted on 25/11/05 at 09:23 PM |
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Set the mushroom inserts so the hole is as far forward as possible, this gives you castor which helps with self centering.
Also i think a bit of toe out will help, but someone will confirm this.
I havent had my self centering tested yet, but when i have driven it on the road it seemed very poor, i though my big heavy pinto and a bit of castor
would be enough, but i might have to try something else if its not enough.
Chris
The Magnificent 7!
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darrensdad
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| posted on 25/11/05 at 09:53 PM |
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toe out at least 25 mm ,,tyre pressure up to reduce the contact patch on the ground try 45psi to start. and take note of what previous mail said about
mushroom.
will never give proper self centering as the geometry of a locost is totally the wrong way. the tester will probably be happy if it starts to self
center
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dom7
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| posted on 25/11/05 at 10:11 PM |
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the holes of the mushroom inserts are as far forward as possible, but ... it's not enough to have a good self centering!!!
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darrensdad
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| posted on 25/11/05 at 10:16 PM |
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toe it out ,then toe it out some more ,it will look stupid i know but it does work . also try a less wide tyre and what i said earlier about high tyre
pressure ,the less tyre on the ground the less resistance to centering.
ps
when it passes dont forget to adjust it back
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bigrich
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| posted on 25/11/05 at 10:49 PM |
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i agree with previous comments holes in inserts to front,toe out and highish front pressures 35 psi+ got mine through sva ok just reset when passed
also not too much front negative camber
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Mark Allanson
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| posted on 25/11/05 at 11:25 PM |
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quote:
Originally posted by greggors84
Set the mushroom inserts so the hole is as far forward as possible, this gives you castor which helps with self centering.
Also i think a bit of toe out will help, but someone will confirm this.
I havent had my self centering tested yet, but when i have driven it on the road it seemed very poor, i though my big heavy pinto and a bit of castor
would be enough, but i might have to try something else if its not enough.
Moving the mushroom around will not alter the castor at all, it will only introduce a bit of trail in the stub axle centre.
Adding toe out will just rip the sh1t out of you tyres. and increasing the tyre pressures will lead to a bald patch in the centre of the tyres.
The only real alternatives are redesigning the upper wishbones to give the correct castor, or shimming the top wishbones rearward.
The bodges may get you through the SVA, but will leave you with a car which is a pig to drive.
When I did my SVA, the inspector said that he knew about all the the sefl centring bodges, and would fail any car that was presented in less that true
road going form.
Food for thought
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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flak monkey
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| posted on 25/11/05 at 11:32 PM |
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Surely MK have redesigned the top wishbone by now to stop this issue??!! Its not a huge task!
David
Sera
http://www.motosera.com
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Mark Allanson
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| posted on 25/11/05 at 11:43 PM |
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quote:
Originally posted by flak monkey
Surely MK have redesigned the top wishbone by now to stop this issue??!! Its not a huge task!
David
You would have thought so..
.. still, people seem to have problems at SVA time
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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britishtrident
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| posted on 26/11/05 at 10:28 AM |
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THE MUSHROOM INSERT HAVE NO
REPEAT NO EFFECT ON CASTER
To get more caster angle or to use the more accurate term for he effect used by bikers trail you have to move the upper ball joint (or entire upper
wishbone) backwards.
Actually the self centre problem really is caused by lack of king pin inclination you can't get any more king pin inclination except by running
a lot more negative camber than the ideal setting.
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Mark Allanson
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| posted on 26/11/05 at 03:39 PM |
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BT, How does the KPI affect the self centring?
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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Humbug
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| posted on 26/11/05 at 04:14 PM |
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I successfully followed Mac#1's advice for SVA:
Wind up springs as high as they will go
Toe out till it looks toed out
40psi in the tyres
Drove like a dog but it was changed as soon as I got back from the test
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Mark Allanson
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| posted on 26/11/05 at 11:12 PM |
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quote:
Originally posted by Humbug
I successfully followed Mac#1's advice for SVA:
Wind up springs as high as they will go
Toe out till it looks toed out
40psi in the tyres
Drove like a dog but it was changed as soon as I got back from the test
Surely, you shouldn't have to go to such extreems, the car should be able to self centre without this bodgery.
What do you do after the SVA? It must be a pig to drive, having to wind the steering back all the time.
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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907
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| posted on 27/11/05 at 12:00 AM |
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Hi All,
There's a saying, "If it isn't broke, don't fix it".
But likewise, if it is broke, then mend it.
You can skirt round it as much as you like, but we know that the only real answer is to increase the caster angle.
Now, if that means shimming, remounting or remaking, then that's what's got to be done.
I'v cocked up, made the w/bones to the book, and I will remake them. IMHO it's the only answer.
I don't like it, but it has to be done.
Mark's right, these SVA blokes are not fools.
Paul G
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darrensdad
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| posted on 27/11/05 at 12:08 AM |
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exactly right ,the suspension geometry will never .repeat never give you exact king pin inclination for self centering.
it is a bodge and yes it will rip your tyres up if left as is after the test .
tyre wear is a fact of life ,if you do not wear out your tyes you are not trying hard enough.
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Mark Allanson
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| posted on 27/11/05 at 03:23 PM |
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quote:
Originally posted by darrensdad
exactly right ,the suspension geometry will never .repeat never give you exact king pin inclination for self centering.
it is a bodge and yes it will rip your tyres up if left as is after the test .
tyre wear is a fact of life ,if you do not wear out your tyes you are not trying hard enough.
Will someone PLEASE explain how king pin inclination affects the self centring
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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Bob C
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| posted on 27/11/05 at 08:22 PM |
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Kpi causes the car to lift when the steering is off-centre, especially when combined witha significant scrub radius (eg cortina upright) so it will
have a "self centring" effect when stationary. But I'm also sure the castor effect is more important when moving!
cheers
Bob
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Mark Allanson
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| posted on 27/11/05 at 10:08 PM |
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quote:
Originally posted by Bob C
Kpi causes the car to lift when the steering is off-centre, especially when combined witha significant scrub radius (eg cortina upright) so it will
have a "self centring" effect when stationary. But I'm also sure the castor effect is more important when moving!
cheers
Bob
Surely, it would cause one side to lift and one side to dip, thus negating any effect?
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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gutball
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| posted on 27/11/05 at 11:33 PM |
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*I think* just trying to picture this in my head, that KPI will lift both wheels when turning, as the lowest point will be when wheels are parallel.
This would be with zero caster, with some caster one side would dip and one would rise, until you'd turned the wheel through a certain angle
(same angle and the amount of caster??) and then both would rise.
But I could be making it up. Got brain ache now.
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Bob C
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| posted on 27/11/05 at 11:53 PM |
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Mark - only if you've got significant castor angle . . . . . . . . . . . .
Bob
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DarrenW
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| posted on 28/11/05 at 09:50 AM |
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would the ackerman angles have an effect on self centering capability? It sounds to me that lots of mods have been done over the years to increase
track width to improve cornering but in doing so some of the basic requirements have been compromised.
There must be some software out there that could give correct wishbone sizes and mounting point geometry to eliviate some of the issues faced.
I was always led to believe that road car set up was a compromise on all factors and that se7en suspension (as with race cars) was slanted more
towards handling and performance - hence why self centrering is an issue. What im reading now suggests this si not true and the problem with se7en
suspension is more due to poor design???????
Any comments?
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greggors84
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| posted on 28/11/05 at 08:26 PM |
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Excuse the ignorance, but why will moving the mushroom insert forward not have the same effect as shimming the wishbone backwards? Surely its rotating
the hub round giving you the castor?
Without the car nearby im having to visualise the set up and having trouble seeing the difference.
Thanks
Chris
The Magnificent 7!
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Mark Allanson
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| posted on 28/11/05 at 09:28 PM |
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Where ever you put the mushroom, the balljoint ballcentres will be in exactly the same place, all you would be doing is moving the stub axle centre in
relation to the ball centres (ie, increasing or decreasing the trail)
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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Bob C
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| posted on 28/11/05 at 11:54 PM |
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Hi Mark,
My take on this is that the castor effect relies on the axis of rotation of the wheel down at road level being ahead of the centre of the contact
patch.
That can be achieved just as easily by trail as castor angle so both should be equally valid means of achieving self centring.
After all the castor effect is named after the castors you find on hostess trolleys (!) and the steeering axis on these is exactly vertical - i.e.
there is NO castor angle on castors!
cheers
Bob
PS I keep spelling it castor but that might be castor oil & they might be casters - I'll go and check - 'salright, both spellings are
correct.
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Mark Allanson
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| posted on 29/11/05 at 11:19 AM |
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quote:
Originally posted by Bob C
Hi Mark,
My take on this is that the castor effect relies on the axis of rotation of the wheel down at road level being ahead of the centre of the contact
patch.
That can be achieved just as easily by trail as castor angle so both should be equally valid means of achieving self centring.
After all the castor effect is named after the castors you find on hostess trolleys (!) and the steeering axis on these is exactly vertical - i.e.
there is NO castor angle on castors!
cheers
Bob
PS I keep spelling it castor but that might be castor oil & they might be casters - I'll go and check - 'salright, both spellings are
correct.
I seem to remember that Rorty said that trail behind the castor line a definite no no, but I cannot remember why
We will get the the bottom of this!
If you can keep you head, whilst all others around you are losing theirs, you are not fully aware of the situation
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