Re: alfa-digest V7 #1208 - Excess Caster = Camber Gain

[AlfaNeely@domain.elided]

    I agree that positive caster causes the steering to self center.  I 
believe that a road car should never be set up with negative caster.
    Caster should always be positive.  Consider a bicycle with the front fork 
vertical (zero caster) or worse, the bottom of the fork pointing back toward 
the rider.  The wheel would be nearly impossible to keep from flopping over 
to the side.  With the fork pointing forward, ahead of the contact point of 
the tire with the ground, the wheel will stay straight.  That is what allows 
you to ride a bicycle with no hands.

    John Hoard of GTA Jr. fame suggested setting the alignment with lots of 
positive caster to get negative camber when the wheel is turned.  I think he 
called this "Camber Gain," but I could be wrong.
    When a wheel with excessive caster is turned, it tends to lay on its side 
(in the extreme case), which adds negative camber.  When the alignment shop 
mis read the Alfa workshop manual and set up my race car with 4.5 degrees 
caster, I did not complain.  That just adds to the 2 degrees of static 
negative camber.  As this is a race car, it is set up with zero toe.
     My street spiders all run Alfa specification alignment per the workshop 
manual, except the street racer.  My street racer has stock alignment, but 
one degree of negative camber via adjustable upper control arms.
Ciao,
Russ Neely
Oklahoma City


In a message dated 12/08/1999 9:48:13 PM Central Standard Time, 
owner-alfa-digest@domain.elided writes:

<< 
 Date: Thu, 09 Dec 1999 13:36:24 +1300
 From: "Graham Hilder" <graham.hilder@domain.elided>
 Subject: Caster
 
 In no.1205, David wrote:
 "As far as caster goes, most modern automobiles require positive caster,
 >meaning the centerline of the kingpin axis is farther back at the =
 top...... A car with too little positive caster will run right off the =
 road if you let go of the wheel, but will turn in better, understeer =
 less...... Too much positive caster will cause heavy steering at low =
 speed, (and)  understeer....... "
 
 And Greg wrote:
 "Steering self-centering effect, directional stability, turn -in feel, and
 the like are affected primarily by CASTER......=20
 A caster angle LESS than the kingpin inclination angle will give an
 increase in positive camber on the outside wheel as a car is steered into =
 a turn, giving a tendency toward understeer. (And, vice versa.)....."
 
 On these postings, I was surprised to read David's remark that too much =
 caster would cause understeer, and re-assured to read Greg's indication to =
 the contrary, i.e. that increasing caster would (generally) tend to give =
 less understeer. I remember a wheel-alignment man I once went to reckoned =
 that I shouldn't spend too much time experimenting with yet more neg =
 camber to reduce my understeer..... no, he said, go for more caster, =
 that's where it's at. And it does seem inuitively right, in a general way =
 on an average suspension layout, that with more caster, you'll gain more =
 neg camber as you turn the wheel, hence achieving the desired result. =
 Unfortunately, on the car concerned, the caster isn't adjustable (without =
 considerable mods), so I haven't been able to try it out in practice.
 
 Regards,
 Graham in NZ
 (71 GTV, 77 Alfetta, 82-82-84 Alfasuds)
  >>

------------------------------