Self centering

[robo]

I have not gone for the sierra set up so I cant comment on it but dig about with the search and its was made clear that the offset mushrooms were used to give the suspension trail. That might or might not be correct so moving on to the basics and there is not enough caster in the system to give it self centering end of. i have gone for the mazda rx8 uprights and will be making fully adjustable top wishbones to address the problem. Caster is what is needed. If the mushrooms set the trail to zero that makes the whole thing worse!! Zero or close to zero caster and zero trail "no thanks"

Bob

[DRCorsa]

You don't merely need caster angle. What you need is the benefit that caster angle gives you. This "benefit" is actually called "mechanical trail" and this along with the "pneumatic trail" gives the "total trail".
Caster is one way to obtain mechanical trail. Another way is moving the kinpin forward of the wheel center.

Mechanical trail is not an "angel". You dont need "much" of that, because if pneumatic trail is only a small percentage of the total trail, then when you are at the limit of traction (where pneumatic trail tends to disappear) you will not get a good feel of it.

[robo]

.
Caster is one way to obtain mechanical trail. Another way is moving the kinpin forward of the wheel center.
[/quote]

Which we wont be doing as we are using ready made uprights so caster it will have to be. Unless of course we fabricate our own uprights! I have checked the mazda uprights the best I can and the king pin line runs through the center of the stub axle so there is no trail built into those particular uprights. All valid stuff this and needs looking at.

Bob

[DRCorsa]

Offset mushrooms is another way to obtain some mechanical trail and you don't need any special uprights to do this.
What i want to tell is that caster is not what you actually need. What you need is trail and there are a number of ways to get trail including caster angle.

[robo]

You're missing the bit that Sierra's upright has negative trail, and offset mushrooms set it to zero, making the wheel axle intersect the kingping axis.
Quote.

Alga has already pointed out that the mushrooms set the trail to zero<which i was told gave a positive trail> so where do the sierra upright boys go now. More caster.?????? We have what the donor of our choice gave us and the only practical way to rectify the problem is to frig the top wishbone or pivot points. Any other method would involve purpose made uprights which no one is going to do.

Bob

[alga]

Robo, here's a piccie of the Sierra upright. The negative trail, while exaggerated, is fairly obvious.



The book design has the caster angle of approximately 5.5°, which, while not a lot, is far from zero.

[alga]

Hm, moving the upright back by 2.5 mm will increase the caster angle to about 6.15°. That's a pretty small difference, I doubt it's worth it.

Actually, making another set of top wishbones with larger offset might be the neatest way to increase the caster. The question is, by how much?