if the off set on the front upper wishbone sets the castor angle and the castor angle helps with the return steering has anyone come up with a revised off set, and if so what is it, for the wishbone to help with the steering so you dont have to prat about with toe in or out for the sva and to make the car drive any better.

the book is wrong slightly, its dimensions give 5.30' rather than 5.3 degrees or somesuch. Selfcentering can be assisted by having the tyre pressure suitable low (i believe that this helps the castor angle work, by creating slightly more resistance to movement).

several posters have reported that 5.3 degrees provides adequate self centering. not everyone though!

Joel,
I think the book is actually a bit more "wrong" than you are suggesting here. I think as it stands the book will only give you around 2.5 - 3 degrees of castor and as you rightly say, more like 5 - 5.5 is required.

Myself and others have worked out the offset required as a distance and I think it was just over 20mm. I'm sure someone will have the figures to hand and will respond shortly - (exits stage left...)

(re-enters stage)
Forgot to mention, I think increasing toe-out also helps make the best of whatever castor you happen to have so you can maybe boost it a bit on SVA day with a little bit of extra toe out.

Cheers,
Craig.

This works
Rescued attachment Wisbone Modification.JPG

I made my top wishbone to give the 22mm dimension as shown above (but mine are book-style 'bones). I get a positive and firm self-centering action with normal tyre pressures (18psi) and 1 degree of toe-in. Got good comments at the SVA!

David