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Castor - Negative or Positive?
speedyxjs - 6/11/08 at 11:17 AM

Looking at Dave Andrews page i saw this:



Do i want Negative or Positive castor?


mookaloid - 6/11/08 at 11:21 AM

Negative for self centering

quote:
Originally posted by britishtrident
quote:
Originally posted by mookaloid
Negative for self centering


No positive --- the drawing is wrongly labled


Edit: Ok it should be as in the one labelled negative even if it is labelled incorrectly

[Edited on 8/11/08 by mookaloid]


mikeb - 6/11/08 at 11:23 AM

assuming the king pin line is the front wheel, negative castor angle.|
The more king pin inclination hence castor angle the more mechanical trail which gives you self centering hence steering stability.


speedyxjs - 6/11/08 at 11:33 AM

Ok. How much do i need and how will i measure it when fitting brackets?


britishtrident - 6/11/08 at 11:47 AM

The drawing is wrongly labeled


britishtrident - 6/11/08 at 11:49 AM

quote:
Originally posted by mookaloid
Negative for self centering


No positive --- the drawing is wrongly labled


britishtrident - 6/11/08 at 11:57 AM

Not often Dave Andrews gets it wrong but this how it should be.
Negative caster is used on some front wheel drives -- Mainly BL Minis to give stability while accelerating.

Positive caster for RWD car -- light cars need more than large cars. Rescued attachment fronta.gif
Rescued attachment fronta.gif


britishtrident - 6/11/08 at 12:04 PM

http://crcc.org.uk/rc-technical.php

http://en.wikipedia.org/wiki/Caster_angle Rescued attachment positive-caster.jpg
Rescued attachment positive-caster.jpg


Alan B - 6/11/08 at 12:17 PM

quote:
Originally posted by mikeb
assuming the king pin line is the front wheel, negative castor angle.|
The more king pin inclination hence castor angle the more mechanical trail which gives you self centering hence steering stability.


Actually isn't king pin inclination the angle when viewed from the front?


Hellfire - 6/11/08 at 12:35 PM

quote:
Originally posted by speedyxjs
Ok. How much do i need and how will i measure it when fitting brackets?


That depends on what type of driving you intend doing. Anywhere between 0 to 7 degrees. Most aim for about 5 degrees. It's the shape of the top wishbone and not the wishbone brackets you need to be overly concerned about. Obviously the brackets need to be to the same dimensions either side (within tolerance).

Phil


iti_uk - 6/11/08 at 01:09 PM

quote:
Actually isn't king pin inclination the angle when viewed from the front?


You're thinking of camber. Castor is, as above described, the angle between the kingpin and the vertical plane, +ve if "tilted backwards", -ve if "tilted forwards".

You want +ve castor and -ve camber.

Chris


g.gilo - 6/11/08 at 03:06 PM

hi
i get a bit woried when you read a post like this one, some of the guys giving advice and i assume building a car seem to be a little short of the correct terms / skills ?
looking at the car from the front, draw a line through the centre of the top and bottom ball joint and that is your king pin inclanation, castor is when you look at the same line from the side of the car. simple. graham.


matt_claydon - 6/11/08 at 06:09 PM

quote:
Originally posted by g.gilo
hi
i get a bit woried when you read a post like this one, some of the guys giving advice and i assume building a car seem to be a little short of the correct terms / skills ?
looking at the car from the front, draw a line through the centre of the top and bottom ball joint and that is your king pin inclanation, castor is when you look at the same line from the side of the car. simple. graham.


This is correct. KPI is not necessarily the same as camber though as that depends on the geometry of the hub/upright. This diagram show zero camber but considerable KPI:


Alan B - 7/11/08 at 08:51 PM

quote:
Originally posted by iti_uk
quote:
Actually isn't king pin inclination the angle when viewed from the front?


You're thinking of camber. Castor is, as above described, the angle between the kingpin and the vertical plane, +ve if "tilted backwards", -ve if "tilted forwards".

You want +ve castor and -ve camber.

Chris


Nope...I'm not.....definitely thinking of KPI..which is definitely measured in the front view (as is camber also)...I don't disagree with your definition of castor.....just being clear about KPI that's all

[Edited on 7/11/08 by Alan B]


britishtrident - 8/11/08 at 09:09 AM



(1) Drawing on Dave Andrew's site is WRONG with regard to caster .
(2) In positve caster the virtual kinpin line tillts backwards when viewed from the side as in the drawing below
(3) RWD drive cars normally need positive caster
(4) With ball joint suspension to get positive caster the upper ball joint centre should be aft of the lower ball joint's centre.


If in doubt check the above in any authoritative automotive text book.

positive-caster.jpg







[Edited on 8/11/08 by britishtrident] Rescued attachment positive-caster.jpg
Rescued attachment positive-caster.jpg


britishtrident - 8/11/08 at 09:25 AM

quote:
Originally posted by matt_claydon

This is correct. KPI is not necessarily the same as camber though as that depends on the geometry of the hub/upright. This diagram show zero camber but considerable KPI:



Nice illustration 100% clear


Syd Bridge - 8/11/08 at 11:05 AM

I've kept out of this so far, but,

quote:
Originally posted by g.gilo
i get a bit woried when you read a post like this one, some of the guys giving advice and i assume building a car seem to be a little short of the correct terms / skills ?



Amen to that brother!!!! Some of the noisiest on this forum have the least proper knowledge. And worst of all, rely on that cursed Wikipedia for their misinformation, or what they read on other similarly misinformed forums.

Castor...is ALWAYS POSITIVE. ie. Kingpin or effective kingpin angle leans back at the top when viewed from the side. Negative castor is suicidal. Does the opposite of self centering.

KPI...Is always positive. But can be zero on occasions. ie. Viewed from the front, the effective kingpin angle leans in at the top. Never negative, for the same reasons above.

Cheers, Syd.


Rod Ends - 8/11/08 at 02:51 PM

Positive camber!