tegwin
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| posted on 10/3/08 at 06:56 PM |
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Self centering....again..
Sorry to start yet another "self centering" thread....But im really stuck with this one...
Im really struggling to get the car to self center....
My caster angle is around 6-10 degrees and the wheels have a definate toe-in.... The camber is pretty much zero , which is not ideal!..The front
wheels are running at 35PSI....
Its on sierra uprights, so there is nothing much I can do about ackerman!
With that setup I get a teeny tiny little bit of pull back to center, but its deffinately not enough....
So what can I change to get more? Is it going to be a case of needing a lot more camber?....less toe-in?.....
Its one of those things thats really getting under my skin
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Paul (Notts)
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| posted on 10/3/08 at 06:59 PM |
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Do you get any self centering in reverse...May sound funny but I spent ages tring to get it to self center with the same set up as you only to find a
small amount But then in revrse it woked well so I swithched to a small amount of toe out and hey presto..
Paul
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tegwin
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| posted on 10/3/08 at 07:04 PM |
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Amusingly enough....I do get more in reverse than I do going forwards
How retarded is that....I will try sticking in some toe out after my dinner and report back....
If that solves it, thats one bloody massive relief
[Edited on 10/3/08 by tegwin]
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Would the last person who leaves the country please switch off the lights and close the door!
www.verticalhorizonsmedia.tv
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zilspeed
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| posted on 10/3/08 at 07:09 PM |
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quote:
Originally posted by tegwin
Sorry to start yet another "self centering" thread....But im really stuck with this one...
Im really struggling to get the car to self center....
My caster angle is around 6-10 degrees and the wheels have a definate toe-in.... The camber is pretty much zero , which is not ideal!..The front
wheels are running at 35PSI....
Its on sierra uprights, so there is nothing much I can do about ackerman!
With that setup I get a teeny tiny little bit of pull back to center, but its deffinately not enough....
So what can I change to get more? Is it going to be a case of needing a lot more camber?....less toe-in?.....
Its one of those things thats really getting under my skin
You really could bugger about with this for a long long time.
Or
You could bite the bullet and remake the top wishbones to either have the correct castor angle as a preset amount, or make them adjustable so that you
can dial in the desired amount of castor.
If you can't do this yourself, maybe you could find somebody to do it for you.
I've driven a car with zero self centring and it was not at all pleasant.
Having to bugger about with spacehopper tyre pressures and ludicrous amounts of toe out are always going to be a bodge. A proper fix wouldn't
take much longer.
I'm an inveterate bodge, but there comes a time when the only job is a proper job.
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britishtrident
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| posted on 10/3/08 at 07:32 PM |
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What is the fore-aft relationship between the steering rack and the track rod ends -- I am guessing the rack needs to be relocated backwards a bit to
give quasi-acer man ie toe-out in turns.
Also lower the tyre pressures -- try 14 psi.
[I] “ What use our work, Bennet, if we cannot care for those we love? .”
― From BBC TV/Amazon's Ripper Street.
[/I]
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lotustwincam
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| posted on 10/3/08 at 08:32 PM |
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As per British Trident, 1st step is to lower the tyre pressures. 35 PSI is too high.
We had same problem, and remaking the top wishbones to give more castor made no difference at all.
A tad of toe-out, cured the problem. Despite what others might say, straight line stability is not a problem. Nor is tyre wear.
Drew.
[Edited on 10/3/08 by lotustwincam]
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nitram38
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| posted on 10/3/08 at 08:41 PM |
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The top bone is set further back than the bottom one at the ball joint?
Or is it it set forward?
If it is set forward, then self centre would work better when you drive in reverse.
Just better check first before you spend days trying to adjust things.
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pajsh
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| posted on 10/3/08 at 08:53 PM |
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I failed my first SVA on self centering and had the top bones modified with rose joints so I could get the top sufficiently behind the bottom bones.
Difference is about 26mm IIRC and was only about 10-15mm to begin with.
I tried all the toe in/out tyre pressure tricks the first time and failed.
I don't think there is any real substitute that to have 6 or more degrees of castor.
Was not the easy option but it worked.
I used to be apathetic but now I just don't care.
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JoelP
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| posted on 10/3/08 at 09:05 PM |
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lower tyre pressure helps as it increases drag, which makes any geometric influences have more.... influence. 
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David Jenkins
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| posted on 10/3/08 at 09:26 PM |
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You might like to try one of the tests my SVA man did - at zero speed (or as near as makes no difference, if it makes turning easier) put your wheel
to full lock, let go of the wheel and gently pull away - make sure that you've got plenty of room!
If you've got decent self-centering you'll find that the wheel pulls strongly towards the straight-ahead position - it might not make it
all the way, but a good strong pull from full lock is encouraging.
David
BTW: My tyres are all at 18psi - 16psi was too squishy and 20psi was getting too hard. The car has 0 degrees toe-in (or 0 toe-out?  ), but I did
modify my top bones to get a decent castor angle.
[Edited on 10/3/08 by David Jenkins]
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