Redid my front end last winter and without any shims I am at 1 degree neg Camber and 1/2 degree pos Castor. If I add shims to increase castor the Camber goes positive. So, I have been considering moving the pivot point on my LCA inboard. According to my calculations .2 inches of movement on either end of the spindle equals 1 degree of camber. I have also heard that many in the vintage race circuit shorten their UCAs covertly to get better geometry which would also fix my issue. I would like to get to 2 degrees neg camber and 5 degrees pos castor. Not that I would use it all but would like to be able to get there. Probably will settle at 1 degree neg camber and 4 to 5 degrees pos castor for Autocross and occasional track days. THe car is driven on the street quite a bit.
1) has anyone else done this calculation and do these numbers jive? e.g. for every .2 inches I move the LCA pivot inboard, I get one degree of neg camber which could be traded for castor.
2) has anyone shortened their UCA - What does that do for the front end geometry. Obvously I would get more negative camber as the suspension compresses. Are there any down sides? How much did you shorten it? I heard 1/2 inch.
I am also thinking that a shorter UCA will give me more tire to fender clearance which wouldn't hurt if I decide to go lower on my stance.
3) One last thing I heard recently is that people are repositioning their spring perch an inch outboard. Seems to me that would equate to increased spring rate and shock response. Why did you do it and were you happy with the result.
4) How much Castor can adjustable struts add? I have heard it's just for fine tuning or can you add several degrees?
A few things: I can't use adjustment kits for the LCA because I have a cross bar that picks up the pivot bolts on the LCA. I'm too cheap to buy after market tublar UCA/LCA peices and I Love to weld and am looking for a winter project.
I've got just a little experience with this stuff, so I'll take a crack at it.
1) Your numbers are pretty close, BTW. There is some benefit to moving the
LCA inner pivot further in. Usually this is accompanied with a longer lower arm.
You also mention at the bottom of your post that your lower arm pivot bolts
are picking up the #2 bolt-in crossmember, ala the Boss 302 Chassis Manual.
Gonna be tough to move your arms in.....
See #4 below for a good way around this.
2) "I have also heard that many in the vintage race circuit shorten their UCAs
covertly to get better geometry"..... Really? Those cheaters! We used to do
those trick UCA's all the time under the guise of "strengthening" them.
I can neither confirm nor deny how much shorter but a shorter arm, lowered about
1 3/8" works awfully well. The car "rolls" negative. It generates a negative camber
curve in other words. Because at ride height this modified suspension is already
past the closest point of approach in its arc, tire to fender clearance is improved.
3) Ohhh, more clandestine stuff. When you move the spring perch location on the
upper arm, you fool with the motion ratio. This has a direct effect on the wheel
rate. So yes, there are some nice benefits to changing this. ANYTHING that
improves tire compliance with the road will be an improvement. A roller spring
perch you might also find to be a good upgrade. Making the spring more
effective is a good thing.
4) You might be able to squeeze 5 degrees pos caster with some of the adjustable
strut rods out there. I've got some massaged '67 units on my GT that'll do 4 degrees.
Because the tire gets closer to the front of the fender lip, you may have do a little
work up there as well.
ex-Global West GM