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Old 06-24-2016, 09:41 AM   #1
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Math Problem: Calculating Loads and Limits

I think I've figured this out, which sometimes means I really may not have figured it out at all, so I need a math check on how I'm figuring my loads. Thanks!

I weighed my truck with a full fuel tank. I got weight at the front wheels 4100#, and rear wheels 3250#.

Then I weighed my truck and RV (truck full of fuel with toolbox loaded and new added 5th wheel hitch AND the RV partially loaded): Front wheels 4100#; rear wheels 5050#; and RV wheels 8100#.

So I figure I currently have a pin weight + hitch and tools weight of (5050-3250) = 1800#; a current total RV weight of (8100 + 1800 Ė hitch and tools weight) = 9900 (max), and a GCVW of 17,250 #.

Truck GCVWR is 22,000. Truck tow capacity is 15,800 for a fifth wheel. Truck load rating for the bed is 6,000. RV max weight capacity is 12,000. So right now I figure Iím OK, since Iíve got a bed load of 1800# and an estimated pin weight of about 1500# (about 16% of current RV weight) and an estimated RV total weight of about 9500#.

Have I figured this right? Thanks for the help!
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Old 06-24-2016, 09:52 AM   #2
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What is the rear axle weight rating?
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Old 06-24-2016, 10:05 AM   #3
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EVERYONE has to work thru this their first time I cheated at first and just posted my 2 empty axle weights, my loaded 3 weights and they told me where to lose weight



No you are making it too complicated... and only being partially loaded makes it guessing, so far

weight is weight - forget tool weight as a separate number, just use your scaled weights...

total weight of empty truck is 4100+3250 = 7350. did you say the trucks base gvwr? say it's 9200, that means you can have 9200- 7350 more weight "carried" by the bed.

what's the axle weight ratings (rear as 1bigmess asked is important) - it has to be more than 5050..

now loaded up:
front 4100(really? the same ????? ours wasn't!)
rear 5050 - tot=9150-compare to your gvwr.
RV 8100
totl 17250 compare to GCWR of truck 22000

you don't have to estimate your pin weight - you know exactly what it is based on the difference of the rear axle weight unhooked versus 5er on pin.... 5050 - 3250 = 1800
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Old 06-24-2016, 10:18 AM   #4
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Quote:
Originally Posted by BobG12 View Post
I weighed my truck with a full fuel tank. I got weight at the front wheels 4100#, and rear wheels 3250#.

Then I weighed my truck and RV (truck full of fuel with toolbox loaded and new added 5th wheel hitch AND the RV partially loaded): Front wheels 4100#; rear wheels 5050#; and RV wheels 8100#.

So I figure I currently have a pin weight + hitch and tools weight of (5050-3250) = 1800#; a current total RV weight of (8100 + 1800 – hitch and tools weight) = 9900 (max), and a GCVW of 17,250 #.
Your results are reasonably accurate, but your method is faulty.

Pin weight is (fGAW plus rGAW) with the trailer hooked up, minus (fGAW plus rGAW) without the trailer.

In your case you get the same answer because your fGAW didn't change with the trailer tied on and added weight in the bed. That probably means your 5er hitch is installed too far back in the bed, or maybe the toolbox was back by the tailgate. When all hooked up, the center of the kingpin should be 2" to 4" in front of the center of the rear axle. That means that some of the pin weight should be on the front axle.

So weigh it again, and this time weigh the tow vehicle with the same weight in it with and without the trailer tied on. Since you already have the weight with the trailer & hitch & toolbox, then just weigh the tow vehicle without the trailer but with the hitch and toolbox. And that assumes that all weights are with a full tank of fuel and driver and the same payload of passengers and stuff. Then you can calculate an accurate pin weight.
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Old 06-25-2016, 08:43 AM   #5
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Rear Axle is 6,000. GVWR is 12,000. I think you are both right, Smokey and JohnBoy - I've made it too complicated AND used a faulty method. I'll weigh it again, with and without the 5th wheel, because obviously there should be more weight on the front axle when I'm hitched up.
Thanks for helping this "Newbie" - I really appreciate the kindness RV'er's extend to one another. Come Aug 1 we'll hopefully be out there with you, full-timing safely and sanely.
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Old 06-25-2016, 09:53 AM   #6
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Come Aug 1 we'll hopefully be out there with you, full-timing safely and sanely.
Full-timing adds more challenges. You have to haul everything you own when you move from one location to another. So weight limits are even more important. Full-timers are much more likely to be overloaded than ordinary weekend warriors. After you are loaded for a move, then weigh the rig.

Add the weight on the front and rear axles of the TV and compare to the GVWR of the TV. That's the weight limit you're most likely to exceed.

Combine the GAWRs of the trailer axles to get combined trailer GAWR, then compare the weight on the trailer axles to the combined trailer GAWR.

Compare the gross weight of the rig to the GCWR of the TV. If you don't exceed the GVWR of the TV or the combined GAWR of the trailer, you shouldn't even be close to the GCWR of the TV unless your TV has a weakling powertrain.

Weigh the rig in the middle of your third move. It's weird how DW can add weight to the rig without even thinking about it. Things like that cast iron Dutch oven she just had to buy so she could fix you a yummy roast or stew.

Pay close attention to air pressure in the tires. Pump up all trailer tires and the rear tires on the TV to the max cold PSI on the sidewall. Do it the first thing in the morning before the trailer is moved, so you're sure to get "cold" PSI.

Plus I carry a laser temp gauge with me and after towing at high speed for a few dozen miles, I check the temp of the trailer tires at rest stops on the highway. Heat is the tire killer, and dead tires are a PITA. To prevent blowouts on the trailer tires, I mount trailer tires with about 25% more weight capacity than the max weight my trailer will put on the tires. Before I did that, back in my younger days, I had several blowouts on trailer tires. My last blowout on a trailer tire was over 100,000 towing miles ago, so live and learn.
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