Castor Angle? Help 2

[Spimage]

I am running 1.5 deg. castor on my cobra replica,(double wishbone) & find the car is not "Tracking" too well. I plan to fabricate new upper & lower control arms, however, before I do, I am hoping that someone out there can give me an indication as to what an 'ideal' castor angle would be.

 

[GregLocock]

Typical values for road cars are more like 5 to 7 degrees. You also need to consider mechanical (castor) trail - 20 or 30 mm typically.



Cheers

Greg Locock

 

[neutralsteer]

I usually do some calculations to check that the castor trail does not go negative in hard braking, with the vehicle pitching. For this you will need the initial castor, the bump castor slope, and the actual vehicle pitch angle.

 

[F1Mini]

What is Mechanical Caster Trail ?

 

[Warpspeed]

Steering effort certainly comes onto this as well.

Check the scrub radius and wheel offset too.

If you want arrow like straight line stability, you may need arms like Arnold Schwarzenegger to steer it at low speeds.

 

[GregLocock]

Mechanical castor trail is the distance by which the nominal side view steering axis hits the ground ahead of the nominal contact patch, which is vertically below the centre of the steering wheel. There is also the pneumatic trail, which is the distance behind the nominal CP that the lateral forces at the real contact patch act. The total trail, times the cos of the castor, times the lateral force gives the steering torque due tot he lateral forces. A similar sum can be done with the KPI and the scrub radius and the longitudinal forces. Both are important.

The trail is decoupled from the castor angle because the steer axis does not have to pass through the wheel centre, in side view. The distance it is offset is sometimes called the longitudinal offset.

Cheers

Greg Locock