Self centering

[DRCorsa]

Originally Posted by 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?

Alga, how much caster have you calculated for the original setup?
After a bit of work on CAD, i came up with this rough figure.
I assumed a vertical distance of 200.5mm between ball joints (according to this drawing) and a slight divergence between the upper and lower wishbones towards their outer ends (ball joint ends).

According to my calculations, by offseting the wishbone chassis mount by 2.5mm you increase caster by 0.7deg and by making a new wishbone with 10mm more offset you get 2.8deg of caster! For 5mm offset wishbone you will gain 1.4deg

Original setup: 5.73deg
2.5mm offset chassis mount: 6.43deg
new wishbone with 5mm more offset: 7.14deg
new wishbone with 10mm more offset: 8.54deg

[snapper]

Reading a geometry article by Nigel Dean handed out by Track Developments at a Kit Car show he recommends 3 to 3.5 deg for a 7, 5 to 7 degrees for a Cobra
How much are you guys looking for ultimately?

[DRCorsa]

Self-centering is a safety and stability feature.
If you don't get any sufficient self-centering effect with 5.5deg then you have to go for more.
I think that the best solution would be a new top wishbone with 10mm more offset and rose jointed so you will be able to fine-tune the caster angle according to your specific needs.
I will seriously think of making a pair for my car as soon as i finish building it. Maybe earlier than that..

[robo]

Originally Posted by DRCorsa

Self-centering is a safety and stability feature.
If you don't get any sufficient self-centering effect with 5.5deg then you have to go for more.
I think that the best solution would be a new top wishbone with 10mm more offset and rose jointed so you will be able to fine-tune the caster angle according to your specific needs.
I will seriously think of making a pair for my car as soon as i finish building it. Maybe earlier than that..

Thats exactly what I intend to do. The book bones needed an ammendment yonks ago to at least put the caster situation in the picture. Its like the rack being 27mm to long, why have the chassis brackets not been altered 13.5mm on each side to put the bump right. Surely just a few bits like this is going to make a huge difference. Improve the breed with a tinker

bob

[baz-r]

you may as well ditch the sierra upright and go for some light cortina rep front uprights and redo the whole lot in one go

you cant polish a turd and rolling it in glitter is messy

[DRCorsa]

A first mock-up:

[The V8 Files]

Originally Posted by baz-r

you cant polish a turd and rolling it in glitter is messy

Apparently you can

http://www.youtube.com/watch?v=yiJ9fy1qSFI

[alga]

Originally Posted by AdrianH

I know you Alga may be going off a different book over there then our IVA manual, but I wonder if every one expects perfect return to dead ahead steering when pushing a car forward, it will not.

Well, I experienced no self-centering whatsoever when moving forward, at any speed. But it does self-center in reverse, and it does work by just pushing the car back with the steering at full lock. The steering wheel starts turning.

Setting to close toe to about zero did not have much effect. I'll try playing with camber next. Also, I'll try changing the wheels to the stock 14" pressed steel ones.

[alga]

Originally Posted by DRCorsa

Alga, how much caster have you calculated for the original setup?
After a bit of work on CAD, i came up with this rough figure.
I assumed a vertical distance of 200.5mm between ball joints (according to this drawing) and a slight divergence between the upper and lower wishbones towards their outer ends (ball joint ends)

My "tape measure applied to the side of upright" measurement indicated the distance between balljoints is about 210 mm. I based my calculation on this length, and it works out at 5.5° then. But, this does not take KPI into account, so, looks like your numbers are more accurate.