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Very strange.
Chippy - 21/4/06 at 10:33 PM

Reading my Haynes Sierra manual I note that the caster is stated as one point five two degrees, which doesn't seem a lot. On the book for my Citreon Xara it states one point three degrees, but then goes on to say Kingpin angle ten point five degrees. Surely the kingpin angle is the caster angle, or am I missing something here. What do the expert say?. Regards Ray.

alister667 - 21/4/06 at 11:35 PM

OK I'm no guru, but as I understand it the kingpin and castor angles are different. The castor is the angle the line of steering rotation (ie between top and bottom ball joints) makes with the vertical as viewed from the side.
The Kingpin angle is the angle the line of steering rotation (ie between top and bottom ball joints) makes with the vertical as viewed from the front.
The castor is the angle front to back, the kingpin is the angle leaning in towards the centre of the car.
I think.
Hope that makes sense.

greggors84 - 22/4/06 at 01:54 AM

Kingpin has more to do with Camber than castor, that may be where you have got mixed up.

nitram38 - 22/4/06 at 03:26 AM

Kingpin inclination, tilts your front wheels into the turn so that the camber change means there is more contact patch of your tyres in contact with the road.
Castor is the angle that forces you wheels to self center. It is abit like the castors on a shopping trolley in that the wheels will always point in straight ahead if you take your hands off the wheel.

Syd Bridge - 22/4/06 at 11:07 AM

quote:
Originally posted by greggors84
Kingpin has more to do with Camber than castor, that may be where you have got mixed up.


KPI is more a function of fitting everything in and clearances, then aiming for centrepoint steering and accepting what can be done in the confines given.

Castor is there to give self centering, and to overcome the effects of kpi only in some very particular circumstances.

Purpose designed racecars have very little kpi, and caster to suit the drivers need for how he wants the car to feel.

Cheers,
Syd.

Chippy - 22/4/06 at 10:58 PM

Hi Syd, I made a bit of a mistake when I said that the Xara had one point three deg's of caster, it has in fact only got zero point three deg's. I actualy got under today and could see exactly what you mean, about the KPI. Maybe you can say why we need 5+ deg's on a locost to get any self centreing, while cars like the Xara don't. Regards Ray

greggors84 - 23/4/06 at 05:00 PM

Less weight on the front end of a locost? Usually the reason why BECs have a harder time than CECs. You need some weight to push the wheels back straight.

Liam - 23/4/06 at 06:02 PM

Caster angle sets up trail - i.e. the tyre contact patch is behind the line where the steering axis would intersect the road, viewed from the side. It's the trail that gives self centering. However you dont necessary need caster angle to create trail - you can just move the axle line backwards behind the steering axis. A shopping trolley is the best example of this - the caster angle is actually 0 but there is considerable trail giving the self centering. Maybe the citroen upright/strut geometry incorporates some trail without caster??

Liam