The factory manuals list the front toe as being set "pressed with 15 kp". I'm trying to fully understand this and thought I'd run my logic past all of you to see if you think i'm right.

kp stands for kiloponds, which is the gravitational force on 1 kilogrom. So 15 kp would be the gravitational force on 15 kilograms.

The 'english' equivalent would be pound-force and 15kp converts to 33.069 pound-force.

So this would mean that the alignment should be done 'pressed with 33 pound-force', which would mean to me, with 33 lb in the trunk.

Or put more simply, the alignment should be done with the spare tire in the trunk.

Agree? Disagree?

OK???

What if I have 75 lbs of radiator in front and the spare in the back? Should I drive backwards?

I'm sure that this is a spec to re-create downforce on the front suspension from being in forward motion, thus this is only a preload on top of the oem factory car weighting and distribution

Hmm, downforce from aerodynamics? Hadn't thought about that. Interesting.

Yeah I've been playing with rc cars recently to better acquaint myself with the workings of suspension, these are one of the things considered when setting up suspension. the weighting of the front end and how it will be acting in motion not sitting.

So, in that case, do you agree with my conversion of units? Tossing an extra 33 lbs in the front trunk while setting alignment will comply with the factory method?

...pressed together, >> << not compressed...

I thought kp stood for kilo Pascals.

In any case, the reference means to press outward against the forward side of the front tires (just below the trunk floor) with a spring loaded spreader bar, and then measure the toe.
I made my own spreader bar back in 1985 with a piece of 1/2" od thin wall aluminum tube with wood dowels inserted at both ends. One dowel was anchored, the other was spring loaded. I played with the length of the spring loaded dowel until I achieved an approximation of the force I thought was correct.

edit: a quick google search yields kilopascal is abbreviated as kpa and is a measure of pressure. A kilopond (kp) as McMark wrote is equal to a kilogram of force. If your conversion is correct at 33 lbs force then my spring loaded bar should exert 33 lbs when compressed to the distance between the tires. I recall the force I used being in that range. I still have the bar on the wall in my garage. I no longer use it since most of the cars I align have turbo tie rods.

Found this reference that corroborates what Dave and Chris mentioned. Thanks for the clarification guys.

When I first tried to have my car aligned, the shop turned the work down when they realized they needed a spreader bar.

How do turbo tie rods change the equation? I have them, and would like to be able to tell the next shop if I have the car realigned.

Zach

One of the major areas which affects alignment precision is the rubber inner tie rod joints. Without them the spreader bar will have a much smaller effect on toe measurement.

Sounds like a good reason to go the the turbo tie rods!