miegru
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| posted on 11/2/07 at 11:18 PM |
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Corner weight mathematics?
Hi,
Went to Ikea today with my girlfriend and came back with 8 weightscales (and other stuff not for this forum but hopefully soon to be seen on
ebay..:-))
Ikea was having a sale on good old fashioned mechanical scales ( 0 - 130kg) and the cost only 4.5 Euro each.
The scales are not reliable in terms of numbers (at 100kg they are about 8% off) but they are all consistent to within 1kg at 100kg. I figured that
for corner weight the actuall numbers don't mean too much but that the split percentages are more important. Is this assumtion correct?
So with two scales under each wheel (a piece of wood spreading the load) I started measuring. Downside of this method is that you need two people (one
sitting in the car and one reading the scales).
No here comes the question; if I have 4 readings of me sitting in the car, each one after some adjustments, and 1 reading without me sitting in the
car; is there a way to set up the car further without me sitting in it and use the data I have to simulate me sitting in the car based on data without
me in the car?
I've been playing with percentages but it doesn't 'feel' right.
One more question; I know that without adding ballast it will be impossible to get to a perfect left-right balance. At the moment I am trying to
create a perfect balance left-right in the front, at the expense of the back. Is this correct ?
Rgrds,
Mies
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Peteff
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| posted on 11/2/07 at 11:21 PM |
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Get some bags of sand or ballast in the drivers side up to your weight then do the weighting?
yours, Pete
I went into the RSPCA office the other day. It was so small you could hardly swing a cat in there.
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JoelP
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| posted on 11/2/07 at 11:34 PM |
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i think its more about the diagonals really, to ensure the car isnt being held up by two diagonally opposite wheels, ie rocking on them. If the car
were modeled as a balanced square, each corner would be equal. Adding a driver to one side would make it settle, but it wouldnt rock on the diagonals.
You could increase the lift on the springs to bring it back level again, and i think this is basically what you are aiming for. The corner weight,
IMHO, should represent the weight over it, and not be caused by one spring being too high.
Im sure someone will be along shortly who understands it better though. 
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jamesbond007ltk
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| posted on 11/2/07 at 11:49 PM |
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I did exactly the same thing! Except i went to Ikea and only bought 8 sets of scales. Got some pretty good looks 
Anyway, what Joel says is along the right lines. Also what Pete said is right. You need to simulate your weight in the drivers seta. I did this with
some tool boxes, spare battery, jack etc. (its amazig how much stuff you need to equal your own weight, and i dont weigh much!)
The way i think of it is like a four legged table. If one leg is shorter than the rest the one diagonally opposite is going to come off the ground
when rocked. Therefore the other two legs will be taking the load.
You should be trying to get even distribution accross eachaxle but you should achieve this by adjusting springs as pairs on diagonal corners.
It hard to get right. I tried the mathmatical approach and the practice didnt match the theory. Best way i found was by making incrementle changes and
seeing the affects.
(I guess some might say trial and error! but i am trying to sound knowledgeable here!: )
Hopes this makes sense and helps, bit tired so typing is a bit rubbish and brain is slowing down for the night.
Rich
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DIY Si
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| posted on 11/2/07 at 11:53 PM |
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What ^^ said. The goal is for equal weights across each axle (note not the same as all 4 being equal), and you need to alter them so the diagonals are
equal to each other too. You won't ever really get it to be 100% accurate, so don't worry about a bit out here and there.
“Let your plans be dark and as impenetratable as night, and when you move, fall like a thunderbolt.”
Sun Tzu, The Art of War
My new blog: http://spritecave.blogspot.co.uk/
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jamesbond007ltk
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| posted on 12/2/07 at 12:01 AM |
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quote:
Originally posted by DIY Si
What ^^ said. The goal is for equal weights across each axle (note not the same as all 4 being equal), and you need to alter them so the diagonals are
equal to each other too. You won't ever really get it to be 100% accurate, so don't worry about a bit out here and there.
Exactly. I should perhaps add here that i have never managed to get mine quite right. I have a light front left that does mean its locks up a bit
early. But it is no real problem, just got to be an aware driver, as normal.
As long as they are nearish you should have no problems with handling.
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britishtrident
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| posted on 12/2/07 at 07:46 AM |
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Each corner should be bear the weight it should bear according to the cars (laden) weight distribution.
Do a spread sheet
(1) enter weight for each corner.
(2) Work out,
total weight left,
total weight right,
total weight front axle,
total weight rear axle.
Total vehicle weight.
(3) work out front rear weight distribution and left right weight distribution.
(4) from step (3) work out what each wheel should bear. for example if 500kg car has 45% front 55% rear weight distribution and 60% right 40%
left transverse weight distribution the left front should bear 500*0.45*0.4=90kg
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JB
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| posted on 12/2/07 at 03:54 PM |
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Corner weights
Originally I got both front wheels the same and lived with the rear imbalance, then researched more and went for the method British Trident
describes.
You will get a rough guide with your method using the scales. Having all the scales level is important. If for example you are 1/10" (2.54mm)
out of level and have a wheel rate of 250 lbs inch, you already have a 25lb inaccuracy. The scales will probably move down with weight on them which
makes it very difficult to get them level and stay level with different loads.
John
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