it would be the same thing as the KPI, although i think technically i dont
have a "king pin".
i can change the KPI by remounting the upper control arm lower and closer to
the wheel.
the reason a large KPI is bad is that it causes the camber to go positive as
the wheels are turned. someone suggested the caster should be 1/2 of the
KPI. scrub radius is something i am just learning about, so not sure what
to do about that yet.
thanks!
-james
----- Original Message -----
From: "Rick Brown" <rbrown7@covad.net>
To: "James Creasy" <james@thevenom.net>; <ba-autox@autox.team.net>
Sent: Tuesday, February 18, 2003 4:26 PM
Subject: RE: fatal flaw in my car?
> James,
>
> Are you talking about king pin inclination (KPI) or Caster?
> KPI determines KPI trail, also called scrub radius. KPI is the angle
> between the upper and lower ball joint centerlines as viewed
longintudanlly.
> Increasing KPI trail increases kick back through the steering wheel when
the
> tires
> are subject to aysmetric forces. For this reason, when
> ABS became real common most cars went to KPI angles that gave very
> small scrub radii to minimize the kickback to the steering wheel under ABS
> activation.
> KPI is usually not adjustable and that is why when you change the
> stock wheel offset and theefore change the KPI trail you can get
> more kickback from the ABS (and more torque steer on front driver cars).
>
> Caster is the rearward inclination of the axis between the ball joints
> and is adjustable, within limits, on most cars. This is what causes
camber
> gain when
> the wheel is turned (and also lifting you mention).
> It's primarily there to increase straight line stability and the higher
> the caster trail the more restoring force returning the wheels to straight
> ahead while
> in motion. The camber gain is ususally a side benefit for handling
whereas
> the lifting is a side detriment.
>
> So, I don't see where a large spindle inclination is in and of itself
> going to cause handling problems. Look at the scrub radius,
> caster, static negative camber, toe, roll centers, springs, shocks, camber
> curves, tires, rim sizes etc. to determine why your car isn't handling the
> way you want it to.
>
> --- Rick Brown
> BP Corvette
>
>
>
>
> > > 650-704-0771
> > >
> > > -----Original Message-----
> > > From: owner-ba-autox@autox.team.net
> > > [mailto:owner-ba-autox@autox.team.net] On Behalf Of James Creasy
> > > Sent: Sunday, February 16, 2003 11:53 PM
> > > To: ba-autox@autox.team.net
> > > Subject: fatal flaw in my car?
> > >
> > > someone pointed out that my car has a very high Spindle Inclination
> > > Angle,
> > > about 15 degrees. this apparently causes my negative camber to go
> > > positive
> > > when i turn the steering wheel (plus it jacks up the front of the
car),
> > > and
> > > is likely the cause of the huge amount of understeer i get exiting
> > > corners
> > > (recently i noticed it entering corners too). this is really
> > > depressing,
> > > since i think my only choice is to remount the upper a-arm lower and
> > > make a
> > > new bracket for the spindle to position the ball joint inside the
> > > wheel...
> > > which also means i cant use my 15" wheels.
> > >
> > > what is an acceptable amount of SIA for an autocross car?? any other
> > > ways
> > > to compensate for it?? thanks,
> > >
> > > -james
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