That's a good idea, have you tried it with less offset/zero offset wheels? It's hard enough to find any wide rims that fit the 1st generation RX7 bolt pattern. Actually the rims came with the car so I'm going to stick with them as long as I can.]
I'm ordering some parts to redo my Ackermann,
How are you going to do this short of hacking the steering arm off of the spindle and repositioning it?
I've been thinking about this whole front suspension setting part of any home built car and this response is just putting into words what I've come up with after many years of building cars. The worst handling one being a 1940 Ford dune buggy with 48" cut out of the w/b!!! But it was the most fun to drive.
To answer your question:
I've been playing around with two suspension programs for months now and I've come up with two easy to do things that hopefully will help correct/improve my bump steer, steering geometry and steering wheel turn ratio quite a bit.
The steering arms right now are the stock RX7 ones which had a different track and w/b as compared to a Locost. My CMC as delivered, bump steer right now is ~1/2" toe out for 5/8" dive!! My friends CMC has about the same amount with his CMC Toyota suspension. Both are rear steer and the racks can't be moved far enough to the rear to correct the link angle.
That's what happens when the original "designer" just throws various spindles onto various length A arms and doesn't take into consideration track and w/b. And then add in the fact that the the spindle tubes aren't long enough and ............. [ouch].
Surprisingly, I don't notice much affect of the bump steer when driving the car. If one wheel runs over a sewer lid in a turn the car will dart about just a little. But that's running at about 1/10 and not 10/10s.
My CMC stock setup right now has the outer ends of the upper and lower A arms closer together than the mounting ends. By using the suspension programs I found that I can get some camber gain in dive by raising the outer end of the upper A arm 1". I should be able to make a 1" thick steel spacer [more unsprung weight] to raise the upper A arm studded Heim joint.
I can correct the Ackermann by repositioning the mounting points for the outer ends [tie rods] of the steering links from the rack closer to the "kingpin line" and moving them 1° closer to the center line of the car. I'll leave the original tie rod mounting points on the steering arms until I know that this all works.
The bump steer right now is caused more by the incorrect vertical angle of the steering links than the also incorrect RX7 Ackermann angle. I will also lower the tie rod ends DOWN to the correct point. And they will be adjustable in height for small adjustments.
I've done quite a bit of measuring and staring at the front end and it looks like I can take a 1"x1" by 1/4" thick piece of angle iron and bolt/weld it to the underside of the steering arm to provide a new mount for some Heim rod ends that will change the Ackermann steering angle etc.
By moving the tie rod end mounting points closer to the spindle I'll also change my over all steering ratio [for the same amount of tire angle] from 3-1/8 turns to ~2 turns. Measuring the small angle change is going to be the fun part! Luckily the RX7 the steering arm is removable and the two mounting bolts are on the 0° reference line.
Has anyone made a scale model of the steering links etc of their Locost to draw out the "100%" Ackermann crossing lines? I did and I seem to have found that the Ackermann lines cross the rear axle extension line at only ONE particular steering angle! Any other steering angle causes the cross over point to be ahead or behind the rear axle line. The line of crossing is at about a 30° angle to the rear axle.
I am also able to confirm this by making a series of Ackermann drawings at different steering angles in Acad.
This is hard for me to explain, but I've found that Wishbone gives agreement between the "theoretical and actual" Ackermann if you input some steering rack change [1" for instance] and then change the amount of Ackermann angle to cause the theoretical and actual Ackermann to be equal [correct]. BUT the amount of Ackermann may be way above or below 100% when the tires are aimed straight ahead.
I think there is a big interaction between the "correct" suspension settings [having the ends of the rack in alignment with the A arm mounting points] changing to be NOT correct as the rack is moved to cause a turn.
That's when I decided to just make a scale model out of cardboard and DRAW the Ackermann lines to see what was going on.
"My junk is organized. At least is was when I put it wherever it is." -olrowdy
Completed building GSXR1000 CMC7, "Locouki"http://dmr-architect.com/~locouki/