Eternal's Straight 6 Build Thread

[Davey]

Originally Posted by mr henderson

They look concentric to me too, but I think the consensus is that eccentric is desirable, but not a big deal really.

The effect on the self centreing is minimal, that's mostly set by the caster, which the offset mushrooms have no effect on.

I respectfully beg to differ M'Lud. They look eccentric not concentric and their effect on self centreing is a lot more than minimal as they are your only real means of adjusting the castor angle which is what generates the self centreing action.

D.

[mr henderson]

Originally Posted by Davey

I respectfully beg to differ M'Lud. They look eccentric not concentric and their effect on self centreing is a lot more than minimal as they are your only real means of adjusting the castor angle which is what generates the self centreing action.

D.

Actually no. Consider what it is that sets the caster angle, it's the line drawn between the top balljoint and the bottom balljoint, when viewed from the side. That's the axis that the hub swings around. So you can see that although the mushroom position (if it is eccentric) can have an effect on the trail, it can't affect the caster.

[Eternal]

Tbh I find all the suspension stuff real hard will have to get some of u guys to sort it out when ready!

[twinturbo]

Originally Posted by mr henderson

Actually no. Consider what it is that sets the caster angle, it's the line drawn between the top balljoint and the bottom balljoint, when viewed from the side. That's the axis that the hub swings around. So you can see that although the mushroom position (if it is eccentric) can have an effect on the trail, it can't affect the caster.

Eh?

if you move either top or bottom locating point fore/aft then the castor changes as the relation of centerline to the vertical has changed.

TT

[3GE Components]

The thing to consider here is that the Sierra upright is being used, this is designed for a Macpherson strut, so when used in our application provides a few "issues"

The picture below shows why, the diagram on the left is the hub using a concentic (in line) insert, the right with eccentric (offset) insert. Both have the upper and lower pivot points in the same place, the only difference is the insert used.



As you can see, with a concentric insert the centre line of the stub axle is forward of the line drawn between the pivot points (castor angle), moving it above the the lower pivot. This reduces the trail, this is what gives self centering. By using an eccentric insert you can see that this rotates the hub backwards around the lower pivot to get the stub axle back in line with the line drawn between the pivot points, therefore increasing trail and improving self centering. Castor is only increased by moving the upper pivot point backwards, either by moving the whole upper wishbone or by making a new one.

Hopefully all that make sense.

Kind regards

John.

[Davey]

Yes of course you are all correct. I blame Mr Carlsberg .

D.

[twinturbo]

Originally Posted by 3GE Components

Castor is only increased by moving the upper pivot point backwards, either by moving the whole upper wishbone or by making a new one.

Still a little confused, surely the excentric adapter has the effect of moving the topmounting location, If you rotate the muchroom 180 degrees the position of the upright centerline moves forward/backwards a centimeter or so in relation to the top balljoint ..

TT

[3GE Components]

If you view the chassis from the top you'll see that the ball joints give you a dimension, shown here as X, this is the castor when viewed from the top.

This dimension doesn't change when you fit the inserts (either type) what happens is you move the upright around. It's the line drawn between the ball joints that determines castor, the centre line through the hub will change, but has no effect on the castor.

Kind regards

John

[spud69]

Yes you're right John, but it still helps with the self centering of the steering. Not as much as a normal production car but enough to pass IVA and give you some return to center.

Cheers....Andy

[3GE Components]

Everything is a compromise, but in this case all the parts are fixed and we are trying to put into words what the eccentric inserts do as these are the only parts that can be changed, basically they increase trial for this set up, which is what centres the wheels. Shopping trollies are a good example of trail being used for self centering, thay have zero castor so when push in a direction the wheel will turn to the correct path (self centering) If you've had one that's had a knock, the trail is upset and the wheel wobbles from side to side trying to self center.

If you wish to increase castor you need to move the whole upper wishbone back or the lower one forward. Castor is what gives the car a steady feeling when driving along the road, greater caster angles serve to improve straight-line stability, they also cause an increase in steering effort.

Hopefully that makes things clearer.

Kind regards

John