Mythbuster: continuing project thread of my 1303 '75

[vdubzack]

Originally Posted by Wally

Interesting!
Wasn't Jacobs electronics a US based company?

Yes. And still is but was sold to the company that does Summit racing and the like.(I do believe) The Aussie jacobs is the only direct site.

[Wally]

Looked at my suspension geometry this weekend and as I remembered, the tca is almost parallel with the steering rod (good thing):



Futhermore, for the camber to get more negative, the tca must become rectangular with the imaginary line through the top of the strut and the ball joint, right?
It seems I am still pretty good with the current angle, even when fully suspended inbound (this pic is taken with the wheel/tca-end supported, so in resting position):


My idea to use a ball joint extender will probably give more bump-steer since tca and steering rod won't be parallel anymore and isnt needed from a camber point of view, so I think I don't want to do that after all.

Next action will be to see what my 'scrub radius' actually is:


Haven't done this part (ran out of time), but will do as well

[Wally]

I actually did already indeed Rich, just like you described, but think I got the wrong points connected...
With your answer I am a little confused even more what KPI and scrub radius is. MotoIQ had a great article about it the other day, using tie rod(?) and the lower ball joint of our Mc Pherson suspension system. Or is that just the upper and lower suspension point in the picture? Thought the upper one was the tie rod of the steering in the schematic?


However, I took the line through the upper Mc Pherson strut connection with the body and the lower ball joint. Thought afterwards I did it wrong and it needed be through the tie rod and lower ball joint. Maybe I did it correct after all?
Anyways, that gave me a scrub distance of +18mm. Still not sure now if that was correctly measured or not...
Mike specified a distance between 3/4" and 3". With 18mm I am right at the lower bandwidth of that.. a bit more might help. I have a little room in the wheel arch, but I think 17" might be better for track driving anyways, mostly because of wheelweight you feel the negative effect of it most on the front. 7x17" is half an inch less wide and with a few mm more spacer, might just give that added scrub we're after?

Tire centerline above is right against the rim contact path, which is somewhat confusing too. It doesn't seem to be the exact tire centerline..?

I'll post some of the pics I took of that tonight.

[Wally]

I think I found a way to alter KPI on my car: I can change camber with the extra large excenter bolt on the inner side of the control arm, but also still with the lower strut bolt. If I arrange the strut such that it sits most vertical (less camber with the lower strut bolt), and counter this with making the TCA longer with the inner excenter bolt, I will have effectively reduced KPA and increased the scrub whilst keeping the same camber.
That should yield a little better steering self-centering and straightline stability