Moving weight... is there math to predict results?

Fifty

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I’ve got my truck about 52/48 f/r with weight balance once my fat bum and the missus is in.
I think...

I have the opportunity to move the battery from the front to rear, behind the axle even. And if I am going to go through the headache of running all the wire, and building mounts etc, then I’m going to run two batteries.
Keep all 4 LP9’s and the factory radio happy lol.
But in all seriousness, since I’m in the middle of building the front suspension and then I’m headed to deaver in a couple weeks since they are going to redo their leaf pack for this chassis (it’s too short and makes the vehicle sit too low)

anyways, I am wondering, on a leaf sprung truck, is there a normal person understandable mathematical equation for the leverage of placing the weight Behind the axle and it’s effects on the front?

I found the manufacturers upfitter manual for the chassis and it said if you place 100# in the bed on top of the rear axle, 90# will register on the rear tires on a scale and 10# on the front tires on a scale...
If that helps....
 

jon coleman

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truck bed is bolted to frame so it shouldn't matter were you place the lbs., now, that bieng said, it Does make a difference in polar moment, ie if 100 lbs is at the tail gate compared to 100 lbs all the way forward in bed going through the whoops, sorta like if you have 100 lbs in your hand move your arm up and down fast is different the if the 100lbs was up by your shoulder moving arm up and down fast, BUT, there is still 100 lbs pressure downward on your arm, common rDc, show it with mathematical equations😱
 

Fifty

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Lolz. I only want easy math... no hard math. I eat crayons lol.

the battery is 48# and if I pull one from the drivers side of the engine compartment right in front and above the coilover mount.

so I figure 100-102-# if I built a cage for dual batteries where the spare tire used to go under the bed.

I know when I put the two 35 inch spares (104# each with tires) and placed them in the bed between the tailgate and the tire humps in the bed; the front of the truck rose almost an inch. I was surprised that it leveraged the front up that much.
The truck has two different springs, the v6 gas trucks have a 14x580# spring, and 2 inches of preload, the diesel has a 14x670# spring and 2 inches of preload (these numbers are approximate but with in 10#, I’m trying to find my notes)

I had to pull the diesel spring off and put the v6 spring back on. (I was still running the oem multimatic dssv shocks). With the king coilovers, I was able to run a 16x500 spring and it was within preload adjustment barely with spares in.
 

jon coleman

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i was told when building my 1700, get as much rearward, but it will only do so much to a point , you will just have Too much hanging off the back and like i said on inertia,it becomes too much to hang onto in the whoops & hi speed bumpy turns .i bet the class 8-7 leaf sprung guys got lots of good info on it
 

PaulW

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Fifty
So you do not have the individual weight scales?
First year math taught me how to do the calculation for a weight shift. Distance and weight is all you need for the equation.
Read your algebra text or look on the internet for help.
On a 5000 lb rig a battery movement wont change the distribution much like the fuel load from full to empty would.
 

Fifty

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For my truck with a stock tank, at 21 gallons... that’s 133#
Two battery’s to the rear and minus the battery in the front is 150#.... and the leverage of it being behind the rear axle.

will it be noticeable to the front spring rate? I dont know...

And is the pivot point the rear axle or the front leaf spring mount?

Im off to search the web for a leverage equation. I think I have an old book that is only race car math. I’ll see if i can find that and if that has something in it...
 

A-Tech_Racing

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Here is the math:



W = battery weight
a = distance behind rear axle
b = wheelbase
R1 = upward force at front axle
R2 = downward force at rear axle

R1 = (W x a) /b
R2 = (W x (a + b)) /b

So if battery weighs 100 lb., placed 25” behind axle, with 125" wheelbase

R1 = -20 lb.
R2 = 120 lb.

notice how the sum of the two are equal to the battery weight
 
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Josh 8

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Weight x arm = momument.

I know it’s missing a lot, but it works. Every private pilot learns this in ground school. There’s your clue.

Another clue is you need know scale weights for each tire. Then pick a datum point to measure from.

That’s how weight and balance is figured for aircraft. It’s the same as what your trying to do.
 
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Fifty

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So it’s -20# and also the -50# of the battery itself.
So it will be -70# effective front and +120# effective rear...

that will help the balance quite a bit on this truck. I need to get it to a f/r scale but I think that would move it to 50/50 almost exact based upon my conservative estimates.

im not sure my and my wife don’t outweigh the oem weight distribution plus the gear placement... I need to get on scales...
 

Josh 8

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So it’s -20# and also the -50# of the battery itself.
So it will be -70# effective front and +120# effective rear...

that will help the balance quite a bit on this truck. I need to get it to a f/r scale but I think that would move it to 50/50 almost exact based upon my conservative estimates.

im not sure my and my wife don’t outweigh the oem weight distribution plus the gear placement... I need to get on scales...
Do you know know your what your tires weight on a scale?

Until you do your chasing your tail.

Get scale weights and post them up. Even if there just axle weights it more then nothing. Show them. With that some accurate math can be done.
 

Fifty

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104# per wheel/tire combo (its a method wheel and toyo RT 35/12.5/17)...4 on the truck, two in the bed verticle
 

Josh 8

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104# per wheel/tire combo (its a method wheel and toyo RT 35/12.5/17)...4 on the truck, two in the bed verticle
No. I don’t care about the tire or the size.

How much weight is on each tire as the truck sits level on the ground? I am asking what is the scale weight of each tire? I don’t care about the size. Just the weight on a scale. Example, if the trucks weight is 5k lbs and it’s divided up equally that means each tire would weight 1250 lbs on a scale.

After you state this I will want to know the gallons of gas in the tank when weighted, where the center of tank is at in inches from the front bumper and if there is a spare tire on the truck, plus where it is at in in inches from the front bumper. Better yet, take it out before it is weighted. Plus, take all your junk out of the truck before you weight the truck.

More questions to fallow…. It’s math.
 
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Fifty

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Ahhh. Ok. I thought it was weird you were asking for the tire weight.

hopefully I have a way to get this corner weighted at a shop in the next two weeks.
 

Josh 8

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Corner weight is best but if all you do is get an axle weights for both axles it will work fine for forward and aft weight transfer numbers. Just not side to side.
Also, once you have the axle weights, I need to know the distance front to rear in a parallel line along the longitudinal axes of the vehical from the furthest point forward like the tip of the bumper. This distance need to be in inches. Example, ten feet six inches is 126”.


Clue, the only really accurate way to do this with out manufacturers mesuments is to drop a plumb bob from points off the vehicle and measure across the ground.

More questions to fallow. But with all this we will be getting close. Don’t forget about the measurement for the gas tank and spare tire. Also, all the seats in the truck from the point your hip bone sits at.
 

Fifty

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Thank you!!! It’s going to take me a week or two to get some numbers!

I finally got the baja kits parts in yesterday and now it’s time to find time away from wife and kids!!!
 

jon coleman

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here, Fifty, this will speed up the math;
 

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