Truck axle loading, predicting sag

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#31

10-13-2017, 02:39 PM

backtrack2015

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Quote:

Originally Posted by Cavalier240

How much fuel was in the truck? That could potentially account for the 145 lbs difference. Based on my research, the payload rating includes a full tank of fuel, so at ~7lbs per gallon x 34 gallons = 238, if you weren't full, that could account for some of the difference.

I'm trying to run my own calculations and follow your math to get down to per axle curb weight. How were you accounting for the weight of you, your wife, the B&W hitch in the back, and the F1 tonneau cover? You mentioned you backed out those weights to get to 8025 - could you explain your calculations for that?

The 8025 actual weight is pretty easy. That's just a total weight. I took the total scaled weight of the truck (8680) and subtracted the weight of the hitch (267), the weight of the tonneau cover (72), and the weight of my wife and I (380). I then added back in the weight of the fuel I was missing (64 lbs, which is 8.5 gallons at 7.5 lbs/gallon). That should give the weight of the truck itself fully fueled.

In terms of my predicting my scaled weight (prior to rolling onto the scale), that's a bit more complicated.
(1) I took the base axle loads from the 2017 Ford fleet specs: F/R 4479/3020
(2) I calculated the weight of my optional equipment as the difference between my trucks weight (GVWR [11500] - payload sticker [3332] = 8168#) and the base weight of an unoptioned truck (add F/R from step 1 to get 7499). Optional equipment weight = 669 pounds.
(3) I assumed 60% of options landed on front axle and 40% on rear. Giving me a F/R weight of 4880/3288.
(4) Since I was at 3/4 tank of fuel, I accounted for this by subtracting 63.75 lbs allocated 33% front and 66% rear. F/R 4859/3245.
(5) I added the people in the front (380) allocated 58% front 42% rear. F/R 5080/3406.
(6) I added the hitch (267) and the tonneau (72) 100% to the back axle. The tonneau was closed (CG roughly centered over axle) and the hitch CG is basically over the rear axle. F/R 5080/3745.

I hope that all makes sense.

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