Hi Morris, Thanks for the input. I apreciate your thoughts as you seem to have done a lot of research into car setup yourself.
I don't quite inderstand what you mean about the upper control arms? Unfortunately they have to have a curve in them to clear the upper chassis rails. The original cast steel Ford arms are curved also. I had thought of notching the chassis rails to run straight arms but I wanted a bolt in solution.
The majority of the suspension loads are taken through the lower arm and I think the upper arm will be more than strong enough. It's made from 1.5" x 0.120" wall 4130 tube. The only mod I've been thinking on is a bar between the 2 legs to complete the "A" but I'm not sure it's nescesary since the legs on the upper arm are quite short. As far as putting HP through it I think the brackets on the chassis would colapse before the upper arm bent.
I have a friend in the engineering department of one of the local universities and he's offered to do some finite element analysis calcs on the arms. I'll probably take him up on it.
The bump measurements I've done so far are just to get an idea of how it's going. I've got a sheet of 6mm aluminium plate that I've got to finish machining to replace the craft wood. I'm also putting together some revised uprights for the dial indicators that will let me raise and lower the whole stand. This will let me set the suspension at ride height and work back and forth from there.
The rear end problems I've been feeling on the track are now fairly evident from the numbers. When the local tyre shop does the rear wheel alignment he sets the rear toe to 2mm at ride height. If we take it that ride height is 1/2 of the suspension travel then at full droop the car will have about 18mm of toe out on the rear. When I lift on the main straight at Winton and shift back to 3rd for the left hand kink the rear end feels quite squirmy (that's a technical term
). I believe this is because as I decelerate and shift down the weight transfers to the front and subsequent lift of the rear means I have toe out. I stiffened up the damping on all the shocks and this settled down a bit but it's still there. The stiffer shocks reduce the weight transfer and keep the rear from lifting but its a band-aid solution. The real fix is to tune the bump steer out which is what I'm trying to do.
So from your reccomendation of 0.015" of bump per inch of travel I'm aiming for about 2.5mm of toe change over the whole suspension travel. Is that the maximum reccomended or minimum? should I try to tune it to less than that if possible?
I can see some argument for having a bit of bump in there. e.g: As the car pitches into the corner the outside rear wheel turns in slightly and helps turn the rear of the car. What do you think?
Cheers