Random1

Your first point is exactly what I think I have achieved with the ride I height I have set. Operation on the part of the toe curve that achieves this. For a stock ride height I think you'll see toe out on initial compression.

Interested in your second point as well.

Random1

I agree with this too and had not actually thought about achieving actual toe out over all. I was thinking dynamic and the direction the toe is changing, not the actual total toe measurement. Yes, knowing if actual toe out is achieved will be important to understand and possibly avoid in your setup for stability.

Let's see some data!

Forcednduckshn

I'll take some Iphone photos of the CR rear suspension at stock ride height (stock shocks), level with the rear control arm to show the geometry with relation to the toe arm, just as a reference. I'll also take photos with my DA, Degassed Koni Yellows once installed.

Nick

nlink720

Robert,

SPC ball joints measure 96 mm
OEM (CR) ball joints measure 75 mm.

This is from the end of thread to the top of the head. Both seem to use approximately the same amount of thread, so I think 24mm is a good approximation of the actual height difference.

Random1

THE CONCLUSIONS AND OBSERVATIONS RELATIVE TO THE CHARACTER OF THE REAR TOE CURVE IN THIS POST ARE NOT CORRECT - SEE LATER POST ON JANUARY 31, 2012 FOR TOE CURVE MEASURE WITH TOE PLATES AT VARIOUS RIDE HEIGHTS.

Here's a quick and dirty rear toe curve. The method and observations are below. I also posted a youtube video of the curve in action.

My intuitive thoughts (hypothesis) on the toe curve were not correct as shown in this experiment. I owe Matt a beer.

Rear Toe Curve Video on YouTube.com



Observations

1. During compression there is only "toe in" occurring across the full range of motion.
2. When the suspension compresses the laser dot moved down, opposite of intuition. Like Matt G said it is a complex set of pivoting/moving parts, not intuitive.
3. The toe curve appears to get more progressive (non linear) as the suspension compresses.
4. The curve it appears to be linear in the +/- 2 inch range of the static ride height of 12.5 inches or the range from 10.5 to 14.5 inches.

How it was done...

1. The rear shock was removed and sway bar disconnected.
2. A laser pointer was attached to the hub pointing forward and outward to avoid the body. The laser was pointed so that it passed by the center of the front wheel.
3. A sheet of paper with a vertical line was placed 12 feet away from the hub center. A level was used to make sure the line was plumb.
4. A jack was used to place the suspension at different ride heights and a pencil mark was made on the paper where the laser dot was located.
5. The suspension was then compressed to a ride height of 10.5 inches, 2 inches above the set (static) ride height of 12.5 inches.
6. The jack was lowered (rebounding the suspension) while a video was made of the laser point moving on the paper. The last couple of inches required the suspension to be pushed down (to over come rubber bushings) to 17.5 inches for a total sweep of 7 inches.

IntegraR0064

Thanks Rob! 100 internet points for you!

In the interest of peer review though, here's a couple questions:
1) As I understand it you kept the body stationary and moved the hub up and down, correct? This is opposite to how I was envisioning it, but I guess my way has issues too, probably more than yours. Also, it sounds like you pointed the laser mostly forwards toward the front of the car but angled out slightly. Is that right? The main thing with that is that you have to account for the change in position of the hub. In other words, if as you move it up it moves in (which I think it does, although I don't remember the magnitude, I think it would be negligible but I'm not sure) then that will obviously move the laser over without changing your toe. Would you say the hub didn't move in and out at all, moved in and out slightly but negligibly, or are you not sure?

2) Did you measure the horizontal distance between the vertical lines that would go through the points? Like I said it'd be good to get a relative magnitude of toe change.

I'll try this on my AP2 if no one else gets to it first, but it probably won't be for another month.

josh7owens

Rob have you done the math to see what the change in toe is in inches for a 25" wheel or degrees?

Last time we had my car on the alignment rack we raised it a few inches to see a toe change and it was something like .05 each side or something. I'm curious what it actually is per inch in the 12.5 +- 2 inches range

Random1

Now that this is done I would say that the best way to do this is to remove both rear shocks, put the wheels on, use two jacks (one for each side), and do actual toe measurements using toe plates at each ride height (wheels on the ground). Otherwise there is too much going on here to have any confidence of actual toe curve.

So, the quick and dirty (not very scientific) toe curve is likely in error, but it gives a feel for what may be happening.

I'll draw a diagram with the arrangement so if anyone want to do calculations or observations it can be done.

IntegraR0064

Now that this is done I would say that the best way to do this is to remove both rear shocks, put the wheels on, use two jacks (one for each side), and do actual toe measurements using toe plates at each ride height (wheels on the ground). Otherwise there is too much going on here to have any confidence of actual toe curve.

So, the quick and dirty (not very scientific) toe curve is likely in error, but it gives a feel for what may be happening.

I'll draw a diagram with the arrangement so if anyone want to do calculations or observations it can be done.
[/quote]

Good call, I think you're right, that's definitely the most accurate way to do it. Obviously with slip plates, bathroom tiles, garbage bags, something slippery under the tire like normal.

For sure the next time I change springs I'll try this out, and I'm still trying to decide whether or not I'm going to do that over the winter.

mLeach

So here's the problem with that method that someone else pointed out. The entire hub assembly moves toward the body during compression/bump/vertical deflection because of the camber curve. you would need to plot that arc against that curve and measure the delta to understand what that distance means. luckily, that arc can be drawn geometrically because of the drawings available of the suspension pickups.

This is why I suggested pointing two downward to generate a line that describes the angle of the hub relative to your alignment at normal ride height.