Random1

The key word here is "dynamic" relative to toe change. Measuring the compressed toe does not tell the whole story. I like the idea of using a laser to track the toe as the suspension moves through its range. I will be giving that a try. Maybe a video will aid in the "dynamic" part of this test. My thought is that there is a toe out element of this dynamic toe curve and using ride height you can adjust where on that dynamic toe curve your setup operates. We'll see once the data is available. I'll be sure to note where on that curve the rear control arm is in the horizontal (level) position relative to the two attachment points.

That magic feeling that Matt describes is what prevented me from buying an AP2 when I bought my second S2000. I remember telling my wife that there was just something missing in the AP2s (besides the 9K redline ) after driving a few of them both on the street and autocross.

murderedrsx

I might attempt to measure this weekend for shits and giggles. Will keep posted.

IntegraR0064

You'd also have to measure the distance between the hub and the wall/plywood/whatever the vertical line is drawn on, in order to actually translate the distance into toe readings. Unless I'm misunderstanding?

Then basically by measuring the vertical movement of the dot you'd get camber change, and by measuring the horizontal movement of the dot you'd get toe. Obviously make sure the steering wheel is centered. The further away the thing is from the hub the more accurate you can be since a alignment change will result in further displacement of the dot.

This is a pretty cool idea actually, I'll probably try it out while I'm changing out springs in a month or so. I wonder if I could adapt it for easier alignments - make a grid of lines on a piece of plywood. hmmm

murderedrsx

My plan is really simple for doing rear toe deflection. I mean its basically what mLeach is saying. I will take the wheel off. Parking brake on. I will tape a laser pointer to the rotor facing a piece of plywood in from of the rotor. I will mark the laser point at full droop. Then at loaded ride height, and then continue to plot until the damper is out of travel. Then I can measure my marks on the plywood. It doesnt have to be really calculated in terms of "Oh the plywood needs to be mounted here perfect etc". The design just should not change.

IntegraR0064

But then what are you going to do with that information? How do you know how much toe a measurement corresponds to?

All you have to do is measure the distance from the laser tip to the piece of plywood. And then make sure your laser measurements are actually two measurements at right angles on the plywood - one horizontal, one vertical. Horizontal is toe, vertical is camber. If you measure at a diagonal you won't know which contributed the difference unless you also measure the angle of your ruler.

Then with that information some trigonometry can be done to get actual angles. Without that you've just got relative numbers that could be totally insignificant for all you know. In other words measuring an inch of laser movement could be 2 degrees of toe, or it could be 0.00000001 degrees of toe. Only way to know that is knowing how far the plywood is away.

Then just keep in mind that if the laser doesn't move precisely measureable distances...for example if it only moved 1/16", and you're not sure if it's 1/16 or 5/64, then you want to move the plywood further away so it's moving in increments more like inches as opposed to fractions of inches and start over so you can get exact measurements.

The other thing you obviously have to know is how much toe you actually have at ride height - so hopefully you've recently had an alignment or you've marked your alignment bolts or something.

Make sense?

murderedrsx

Yeah that totally makes sense. I would triangulate it much like your saying. I dont think the change in camber is going to affect the horizontal distance. Yes it will be on a diagonal but the distances will be the same despite camber gain. Now that i think about the laser thing is sorta imprecise. Measuring toe from a fixed point along the chassis to the edge of the rotor might be more precise. Anyway i can play with it. I can get lots of data. The ideal thing would be to simply plot the toe vs the suspension compression to look for magnitude and direction of toe change at various ride heights. Although you cant infer degrees of toe from that it gives you a good idea of what the toe curve is doing.

IntegraR0064

I just did some quick calculations to figure out how far you'd need the plywood away from the hub. Toe will move the laser d*tan(toe_degrees) inches, where d is the distance to the plywood in inches.

So for example, if toe changes by 1 degree (which is obviously an insane amount), and the plywood is a foot away, then the laser will move 12tan(1)= 0.2 inches. Not much. A more normal increment of toe would be 1/8" of toe between both wheels, which from memory is something like 0.15 degrees per wheel, which would move the laser .03 inches, which is about 1/32".

So you really need the plywood further away. Anyone have a big garage? lol. 5 feet away wouldn't be too bad, then 1/8" of toe would be around 5/32" laser movement which you can at least get approximate measurements at that kind of magnitude. I think my idea of easy alignments won't work though

IntegraR0064

Sounds good. I don't understand what you're saying about measuring on a diagonal though. Pretty sure you get it but I'll explain more just in case. Camber will affect diagonal measurements - the camber is changing much more than the toe, so if you measure on a diagonal you're actually measuring camber much more than toe. It's not hard to measure horizontally, just make a vertical line where your original reference point is and measure horizontally from the line to the laser as opposed to measuring diagonally from the reference point. Then camber will be taken out. Or like I said, make a vertical and horizontal crosshairs at your original reference point and measure vertical and horizontal separately and you'll have both toe and camber curves.

Measuring from the edge of the rotor you'll have the same problem that the distances are very small, probably worse actually.

ebdavis

If all we want is a toe curve wouldn't it be as easy as getting on an alignment rack and cycling? What we really need is some data on dynamic attitude change during the course of a typical national level autocross. Then we use suspension analyzer software (with a plotted chassis/suspension) to test out different alignment settings and their relationship with whats going on with the other end of the car during these dynamic attitude changes. Somebody should get right on that.

I really think Matt G. is hitting the nail on the head with his appreciation for this toe change. I mean whats really going on here is a purposeful rear-steer (ackerman?) effect isn't it? But I also think with as "alive" as the rear is that you will have to be a zen master to utilize this trait properly lol

mLeach

easier method for measuring the change in toe.

1. place car on stands
2. remove a wheel
3. remove spring/shock assembly
4. disconnect sway bar
5. engage e-brake
6. mount a pair of lasers aimed at the ground on the brake rotor or other flat surface attached to hub.
7. raise hub to ride height, draw line through the two dots. this is your origin line. Be sure to indicate distance between dots.
8. raise/lower hub desired amount and draw new line. next to line indicate the raise/lower amount.
9. use proportional triangles to determine amount of toe change on a 25" wheel.

even if the distance of the line from the orgin changes, all we are interested in is the change in angle of the line. you may need to extend the lines that you draw much farther to get any meaningful measurements, and while not precise, it should be repeatable, and describe the character of the rate of change. i.e. linear, progressive, etc. You should also be able to find the magnitude at full drop and bump.