rear caster

Can anyone give me a clue regarding the effects of caster on the rear. I'm chasing a handling problem on a suspenssion very similar to that on my C3. I've been told never to have negative caster and I do have about six degrees negative. I'm going to adjust it to zero or positive but I thought someone here might help me understand the effect on a nonsteering end?

Rear vette IRS has no caster setting. Only camber & toe.. Caster is the steering axis trailing the wheel to ground contact point, only applies to front suspension and some rear double arm. Never with a trailing arm, semi trailing arm or Chapman strut arrangement. Even the C4 5 bar suspension does not have a rear caster setting, it's a decoupled sort of trailing arm suspension. A Chapman strut is commonly used on the rear (only Lotus ever used them on the front) and is similar to the McPherson strut, with the main exception being that the McPHerson strut turns when steering, the chapman does not (although commonly you will read that chapman struts are the same as mcphersons just mounted on the rear, this is not true).
The C5 & 6 rear suspension is a double arm with a toe control rod that is adjustable for rear toe setting and fixed on the inside. These types of systems can be used to have a caster effect to increase or decrease rear steering and/or camber effect by altering the toe control rod geometry.

Positive caster means the steering axis is trailing the wheel, this gives straight line stabiity, more caster makes it ahrder tos teer. You want 3 to 5 deg. of pos. caster in most applications.

So, what kind of suspension are you talking about?

I guess your talking about the front caster setting?

If your running negative caster the car will wander and it will be hard to keep it going in a strait line.

It is the rear of the car I'm talking about. It uses a variation of a double A-arm with a lower link and a transverse spring supplying the upper A-arm.

I thought it to be pretty much the inverse odf the C# but apparently not. I thought this would be the best place for that type of suspension tuning.

I can understand the centering action and camber gain with caster on a front suspension, steering. Just a bit at sea about the effects on a rear. I guess it would tend to magnify any toe changes durting travel?

What car? What type of suspension?

Negative caster on the rear.... it make a sens.

I guess it is built in the suspension design in order to have some "active steering" at the rearend.

When the external rear tire is working in opposition to the centrifugal force, the system should react with a bit (limited by the bushing deflection) of steering able to contrast oversteering.

My opinion is that this system can be good for "safety" driving..... as anybody knows is more "istinctive" to contrast understeering than oversteering.

For performance driving (...like if you stolen the car you are driving...) the best condition is absolute control of the wheel position.
In other words it must be totally predictable the position the wheel will assume in all the driving situations.

Rigid bushings, strong arms, good control of the roll center position in any bump or rebound contition.

This don't means that the wheel don't have to change his position (camber and toe), but that the position must be controlled and defined.

Usually is common to build some toe-in during bump..... it must be not related to the force applyed to the wheel.... but related to the travel of the suspension.

My opinion, of course!

Except the Porsche Weissach axle where the links were made to purposely deflect (bushings and linkeage rods) to give significant toe in at the rear wheel when it's the outside wheel in a corner and the throttle is let off, this was done to stabilize the rear and keep it from snap steering, something the early porsches were notorious for.

In fact I was thinking to some similar effect.

Thanx guys,
twenty four hours later I'm starting to work my mind around to pretty much what you're saying. The trail contributes to stability. I've spent hours on this suspension adjusting the camber curve and toe without ever regarding castor. This revelation may finally put me into the good zone:mime: