5th wheel weight question

We have a 54 gallon fresh water tank in the very back, which we normally run full when traveling. If we dry camp or do not dump the holding tanks, there is a very noticeable difference in pin weight as the water is moved to the two grey and one black water tanks forward of it. One grey tank is way forward, then black, axles, 2nd grey, then fresh tank in the very back. So if you are not dumping your tanks and moving the 400+ pounds around in the trailer, it is noticeable.

Chris

12thgenusa wrote:
FWIW, I have a 26' 5er with rear kitchen and aft FW tank. I've done the math and 500# of water lowers the pin weight 100# and adds 600# to the axle weight. Your result may vary somewhat depending on length of trailer, size of tank and location of tank.

I usually travel with the tank full, because we mostly dry camp. Handles just fine.

We have a slightly shorter 5er and had about the same results. 40 gal tank at rear added about 500 to trailer, took nothing off the hitch(weights taken at different times, so math doesn't work out perfectly). I can't tell any difference in handling. We also have a second 80 gal tank in the rear, but I have never driven on the road with it full; only fill when entering a campground.

Doug

Thanks for all the answers. I don't have a 5th wheel but was just wondering.

fj12ryder wrote:
FWIW, 1200 lbs. in the rear of my triple axle toyhauler takes 40 lbs. off the pin.

Double or triple axle, it affects the fuzzy math.

I'm pretty certain the reason the fresh water tank is usually at the tail end is because the basement and forward storage is at the front, where most of the heavy stuff everyone brings along goes. Once we've packed everything up for an outing, I usually fill the fresh tank from a little way to all the way full to take some of the extra weight off the pin. The other consideration is if we're going to be dry camping and will need one, two or three days of water.

FWIW, 1200 lbs. in the rear of my triple axle toyhauler takes 40 lbs. off the pin.

If it were a single axle and the distance between the tank and the pin were about the same, yes. But it is a double or even better trippel axle so most of that weight is distributed across those axles and the equalizers between them.
when I put a 1100 lb RZR and a small kids quad and who knows what else in my garage it only takes a couple of hundred lbs off of my pin.

No, 500 pounds of water in your FW tank located behind your rig's axles does not equate to 500 pounds off of your pin weight. It will certainly lighten the pin weight but it won't be exactly the same. Doing the math supplies you with a theoretically accurate answer, weighing it with and without a filled FW tank will reveal real world results.

Jettech109 wrote:
If it is aft of axles yes it will make the pin lighter. Basic CG the axles are the fulcrum. How much? That would require weighing it or a lot of math.

Not a lot of math. The formula for Torque is simply Force x lever arm distance.

1. Calculate the weight of the water.
2. Multiply by the distance from the center of the rear axle to the center of the water tank
3. Divide the answer by the distance from the center of the rear axle to the pin.

The answer should give you an approximate estimate of the weight eliminated from the pin. But it is only an approximate because you don't really have a single fulcrum on a 2 or 3 axle trailer. The fulcrum shifts as you rock forward or backward and put different amounts of weight on each axle. And the springs will also absorb some of the force.

CrowsnestGuy wrote:
I just have a question and it may be silly but I was wondering if you have a 5th wheel and the fresh water tank is at the very back. If you fill it (42 gallons about 500 pds) does it take all that weight off of the pin?

Thanks...

Some, but not all. Suspension and tires take up some of it; it's not a "hard" fulcrum. The tank is X feet long (front to back), so the center of the tank will be the center of the weight acting on the pin. As others have said, you have to be careful of unweighting the pin =too= much or you'll have handling problems. Also, do you want to be hauling that extra 360 lbs if you don't have to? (42 gal x 8 lbs/gal) Only way to be 100% sure is to weigh it ready to camp with empty tank, then again with full tank.

Lyle