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PostPosted: November 21, 2016, 10:01 pm 
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I decided to take a break and corner weight the car as a precursor to finding the cg height. This is with full fluids and half tank of gas. Still not sure why the FL is so much higher than the FR


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PostPosted: November 24, 2016, 6:41 pm 
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Ok so today I used the scales to do a cg height test and got 52" off the ground as a result... doesn't that seem really high?? That's like 7" above the roll bar


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PostPosted: November 24, 2016, 10:33 pm 
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Should be around 16" or so.

Did you raise the front or back of the car? When raised, your front numbers are higher, so unless the rear was raised, that's not right. Maybe try entering the change in weights of the opposite end? Lastly, it says inches, but is it using lbs or kg? When things don't look right it's always good to vet units first.

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PostPosted: November 24, 2016, 11:24 pm 
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I check it with the longacre calculator and got the same values. Here are the weights and it was raised in the rear. 23" tires so I am not sure what could be wrong

I though I heard somewhere that the At-om has a cg 14" above the drivers shoulder so that would be similar to mine.


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PostPosted: November 25, 2016, 1:18 am 
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Doing the calcs by hand I get the same results. Raise the rear twice as high (if possible) and see if you get the same CG heigh. With the difference between the two readings being so low, any error in the scales is going to have a significant influence on your result.


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PostPosted: November 25, 2016, 1:22 am 
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Correct. I also didn't replace the coil overs with solid links. Not sure if that is an issue though.

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PostPosted: November 25, 2016, 9:54 am 
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Did anything move? Perhaps fuel in the tank or a bowling ball rolling around.


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PostPosted: November 25, 2016, 10:00 am 
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I don't know what's wrong with the math or measurements (guessing the car was bound up on the scales in some way) but you absolutely do not have a 52" cg height. I would be surprised if it's much over 20" on a 23" tall tire. Typical values for a sports car with a heavy, full glass greenhouse are right at the top of the tire.

Alex


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PostPosted: November 25, 2016, 10:27 am 
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That's a lot of weight transfer with the rear raised. That's what's driving the CG number up

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PostPosted: November 25, 2016, 11:44 am 
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I will try to lift the rear, then lift the front and put it back down on the scales. If that doesn't work I will run the test backwards like Kurt mentioned

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PostPosted: November 25, 2016, 1:35 pm 
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Location: Cornholio OR "Where the magic happens"
I made a pair of stands to put on top of my scale pads to raise one end of the car to calc CG.

I can swap ends with the stands to verify my math.

A CG 14" above the drivers shoulder does not seem right without a roof mounted storage unit with a few old batteries in it.

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PostPosted: November 25, 2016, 1:46 pm 
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How do you swap the ends? I was just using a jack under the car to lift the rear. I can use my chain hoist and get it a bit higher.

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PostPosted: November 25, 2016, 1:59 pm 
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Location: Cornholio OR "Where the magic happens"
I built cube shaped stands to fit on top of my scale pads.

They are taller than the pad is square, 18" I think.

I don't recall if i was smart enough to take into account how high my jack will lift.

But I have one of those old bumper type air lifts for high work.

Swap by turning car around or moving stands front to rear.

That way I get weights on all 4 wheels using a set of Longacre racing scales.

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PostPosted: November 25, 2016, 2:24 pm 
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Ok so I did both. One with the rear raised 18.5" and one with the front raised 11".

I get 38" in both scenarios and 41" if using the old weight #'s


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PostPosted: November 25, 2016, 2:27 pm 
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Don't you need to raise the ends of the car the same height?

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