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Posted by: McMark Sep 11 2011, 02:05 PM

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?

Posted by: kg6dxn Sep 11 2011, 02:10 PM

OK???

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

Posted by: Ductech Sep 11 2011, 02:31 PM

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

Posted by: McMark Sep 11 2011, 02:33 PM

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

Posted by: Ductech Sep 11 2011, 02:40 PM

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.

Posted by: McMark Sep 11 2011, 02:48 PM

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?

Posted by: dlestep Sep 11 2011, 03:21 PM

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

Posted by: Racer Chris Sep 11 2011, 06:57 PM

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.

Posted by: McMark Sep 11 2011, 08:03 PM

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

Posted by: Vacca Rabite Sep 11 2011, 08:43 PM

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

Posted by: Racer Chris Sep 12 2011, 06:56 AM

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.

Posted by: Bartlett 914 Sep 12 2011, 07:24 AM

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