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  #21  
Old 13th September 2012, 10:22 AM
MikeB MikeB is offline
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Originally Posted by alga View Post
One is as good as the other:



Fixing the Sierra's trail inceases positive caster distance, too. It's the distance between the kingpin axis' projection intersection with ground and the centre of the contact patch, and it is precisely the lever that does self-centering.
Just to clarify,
When you move the inserts, it doesn't change the castor angle as the top and bottom pivots are fixed, it effectively moves the centre line of the wheel forward and backwards changing the trail, so in the diagram above the steering axis stays fixed the wheel effectively moves for and aft.

From recollection the only thing that would give you any self centering when stationary is king pin inclination as this causes the body to rise and fall when the wheels are turned so the vehicle mass forces it back down due to gravity. (sorry missed someone already said this!)
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  #22  
Old 13th September 2012, 11:08 AM
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alga alga is offline
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Originally Posted by DRCorsa View Post
Alga, have you actually measured your car's caster angles in an alignment shop?
No, I haven't. Do you think it's the only way to get a reasonably exact measurement?
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  #23  
Old 13th September 2012, 12:03 PM
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Here is a picture of the 4x4 hub with a steel ruler through the two pinch bolts, I know this is not 100% accurate but it looks like the drift boys are right. It does appear there is no trail + or - , the strut diameter is 50mm so I dont know how that compares. Might be a cheap quick fix. Edit :have a read of this, the cobra builders have the same problems http://www.cobraclub.com/forum/pilgr...or-angles.html




Bob
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Last edited by robo : 13th September 2012 at 12:58 PM.
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  #24  
Old 13th September 2012, 12:10 PM
DRCorsa DRCorsa is offline
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Originally Posted by alga View Post
No, I haven't. Do you think it's the only way to get a reasonably exact measurement?
Absolutely. You will also be able to find out if you have any difference in caster angle between left and right wheel.
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  #25  
Old 13th September 2012, 07:58 PM
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Originally Posted by robo View Post
Here is a picture of the 4x4 hub with a steel ruler through the two pinch bolts, I know this is not 100% accurate but it looks like the drift boys are right. It does appear there is no trail + or - , the strut diameter is 50mm so I dont know how that compares. Might be a cheap quick fix. Edit :have a read of this, the cobra builders have the same problems http://www.cobraclub.com/forum/pilgr...or-angles.html
Very interesting, thanks for the pointers! Alas, RWD sierra's struts are 45.5 mm in diameter...
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  #26  
Old 13th September 2012, 10:08 PM
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Absolutely. You will also be able to find out if you have any difference in caster angle between left and right wheel.
I just realised, it is pretty easy to check to within less than 1 degree with a steel ruler, a square, a reference plane (e.g, wall, big square box, etc.) touching front wheels. Just measure the difference of the distance of centres of balljoints from the reference plane. A measuring error of 1 mm will result in the error of about 16'.
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  #27  
Old 14th September 2012, 09:43 AM
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Really then for the sake of spinning up some 50mm mushrooms and going to the 4x4 hub it would appear that all would be ok for caster and self centering as its the negative trail of the 2wd hub that is wiping out the effect of the caster this built into the suspension system. That would explain why you car self centers when reversing. Best to give tt a nudge and see if there is anything else odd about the 4x4 hub.

Bob
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  #28  
Old 14th September 2012, 04:18 PM
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Originally Posted by robo View Post
Really then for the sake of spinning up some 50mm mushrooms and going to the 4x4 hub it would appear that all would be ok for caster and self centering as its the negative trail of the 2wd hub that is wiping out the effect of the caster this built into the suspension system. That would explain why you car self centers when reversing. Best to give tt a nudge and see if there is anything else odd about the 4x4 hub.

Bob
The lack of caster has been a known fault right from the original design, and I believe has been a problem on the MK as well yet there is still no revision to the design, update of the book in this respect. Unfortunatly most builders don't find this out until they've built the chassis/car so end up having to 'bodge' around the problem.
A solution if you can get them would appear to be the 4x4 upright,but it would be better for a sticky on here relating to this design problem so future builders have the chance to 'build in' some extra castor.
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  #29  
Old 14th September 2012, 05:07 PM
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I have two sets here if someone wants to have a go. What the f@@k do you do with the front cv because it looks like the same system as the front wheel drive cars where the cv holds the whole hub together. I suppose you could cut the cv bit off the shaft and leave enough of a shoulder on there to make it like a big bolt. I think I will muller one and have a look.

Bob
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  #30  
Old 14th September 2012, 08:19 PM
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Well I've been reading this thread and at the moment it's totally incomprehensible to me...
I really need to read up on this I guess. I don't want to hijack this thread ALGA but will the MX5 build suffer the same fate...
Here's a photo





I don't believe anybody has finished a MX5 build on here yet so it would be very nice to know.
I believe Nathan modified his top wishbone to overcome the clearance issue with the steering rack extensions fouling the bottom wishbone and moved the top threaded adjuster rewards.
He stated this helped his self centering as well as a result.
Obviously you are looking for a cost effective solution to the problem but would a new top wishbone as Robo suggested be the only option??

Johno
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