Weight Distribution?? - Montana Owners Club

Wiarton William · 07-23-2008, 01:08 AM

My PIN weight is a little higher than I would like...(2500lbs) and I would like to reduce it, I have discarded anything that I dot really need to take along which has reduced my Gross weight....I know my fresh water tank is behind the axles...and I know that IF I add water to that tank it will increase my Gross weight...IF I was to add 20 gallons/200 lbs of water to the fresh water tank, would I see a comparable reduction at the PIN?????? (as in a teeter totter affect)....thanks

Delaine and Lindy · 07-23-2008, 03:24 AM

I am not sure, I haven't owned a 5th wheel with the fresh water tank behind the axles. I don't travel with water in tanks, with the exception of the black tank just to be able to use the bathroom. I think removing the things you don't use is the biggest change we have made. Since we aren't full timing, we aren't going to get another W/D. And we don't have a on board Generator. I must tell you we never boondock, just prefer all the hook ups. GBY.....

TLightning · 07-23-2008, 04:02 AM

If the tank is just a little bit behind the axles, I doubt adding 20 gallons of water will make that much difference. The farther aft you put the weight, the more effect it will have on the PW.

exav8tr · 07-23-2008, 04:43 AM

I can tell you from my piloting days that it will be proportional, but not exact. The lenght of your trailer is called the arm and this weight is distributed along the arm of your trailer. There are formulas involved when loading an aircraft that are beyond me at this point. Loading a trailer would be very close to those procedures. Perhaps a retired loadmaster could step in here and help you with the calculations. They are quite involved as they also include the center of gravity of the trailer also. One would have to know the CG to be able to calculate the weight shift.

bncinwv · 07-23-2008, 07:53 AM

A simplified approach to doing the complicated lever calculations (as an engineer, I prefer the simple stuff) is to estimate the length from the midpoint between the two tires to the center of the fresh water tank. Then estimate from the same mid-point to the pin. Disallowing for all the complicated gyrations such as spring tensions, axle weight distribution, etc. The difference will be approximately proportional. Simply put, if the distance to the centerline of the water tank is 10 feet and the distance to the pin is 20 ft. The effect on the pin would be APPROXIMATELY half or 100 pounds lighter. As I said, this is an estimate but will get you close. Of course the only way to be certain is a visit to the scales.
Bingo
On edit: the variance should be within 15-20% since that is the percent of total carrying weight that is usually seen at the pin. If you know the percentage you can apply it to the proportional calculations and get even closer. Phil is correct about the CG, this will allow for it.

Waynem · 07-23-2008, 02:47 PM

The answer is "Yes." But how much depends on factors already stated.

Any weight placed behind the CG (center of gravity) will lighten the front of the trailer. Maybe a lot, or a little, depending on the weight and it's position to the CG.

Wiarton William · 07-23-2008, 03:18 PM

I will have to find out how far back the fresh water tank is... the low point drain for the tank is about mid way tween the wheels and back of trailer.........thansk

exav8tr · 07-23-2008, 03:41 PM

Don, there is virtually no way to determine exact CG as that figure will vary based on equipment and options. I think the best way is to weigh the rig and determine actual pin weight the way you load it, minus any water in tank. Then put in a given amount of water and weigh again to determine how much a difference so many gals make on the pin weight.

Given the truck you have and your pin weight it would seem you don't have a problem unless you are a heavily loaded truck to begin with.

Wiarton William · 07-24-2008, 01:37 AM

This all comes down to the differences in towing now compared to the last RV...it was a 5ver but weighed in at about 2000lbs lighter..It feels heavy and lumbersome...I thought that if I could take some weight off the truck I might lessen the strain...We will be heading south in the late fall and I am trying to find ways to make the trip a little easier..

TLightning · 07-24-2008, 04:27 AM

You are going to be towing the same amount of weight, whether it is on the pin or in the coach. IMHO as long as your PW is within the recommended limits (15% to 25% of the gross trailer weight), I would not worry about it.

Wiarton William · 07-24-2008, 07:04 AM

Ok...I worked it out and it is 25%.. thanks

You may also like: