Im sure this has been covered here before somewhere but, i'm using sierra uprights and i need some info on castor angles,im not sure about the relation between top and bottom b.j's etc..anybody enlighten me.??

Looking down on it it.
Top behind the bottom.
Steve.

castor is the angle of a line drawn from upper to lower balljoint, from vertical when viewed from the side. Upper to the rear is the norm.

Yep as above - if you aim for the top balljoint to be about 20mm behind the bottom one (with a bit of adjustment either way if poss) you'll not be far off.

Geoff

Thanx guys ,great help..