Estimating Pin Weight Changes

[BobKilmer]

I recently posted about estimating maximum pin weights for a Momentum. I thought it would be helpful if I posted how in general to estimate the impact of adding or subtracting weight to an RV impacts the pin weight.

I created this diagram to help illustrate the data needed to estimate the pin weight change:



From the diagram:
W is the weight to be added (pounds)
Xw is the distance from the center of the axles to the center of the weight (feet)
Xp is the distance from the center of the axles to the pin (feet)

The weight change for the pin (Wp) due to adding the weight W at location Xw is then:
Wp = W*Xw/Xp
This is a weight change, so the change Wp is added to the original pin weight to get the new pin weight.

Some things to notice are:
- When Xw = 0 (all the weight is over the axles), Wp = 0. This makes sense, all the load is carried over the axles.
- When Xw = Xp (all the weight is at the pin), Wp = W This also makes sense, all the weight is being carried at the pin.
- For a toyhauler, Xp is often negative since the weight is in the garage behind the axles. This leads to the pin weight being reduced by adding garage weight.
- W can be negative, so the same formula can be used to show the impact of removing weight as well as adding weight.
- W can be due to cargo changes or fluid changes.
The formula can be also used for multiple weight changes at once by adding each Wp, so changing weights and fluid levels can be put into a spreadsheet if desired.

[BobKilmer]

There is a mistake in my post. The following line is wrong:

"- For a toyhauler, Xp is often negative since the weight is in the garage behind the axles. This leads to the pin weight being reduced by adding garage weight."

That line should say Xw is often negative for a toyhauler, not Xp. Sorry for the confusion.

[Malco1]

I recently posted about estimating maximum pin weights for a Momentum. I thought it would be helpful if I posted how in general to estimate the impact of adding or subtracting weight to an RV impacts the pin weight.

I created this diagram to help illustrate the data needed to estimate the pin weight change:



From the diagram:
W is the weight to be added (pounds)
Xw is the distance from the center of the axles to the center of the weight (feet)
Xp is the distance from the center of the axles to the pin (feet)

The weight change for the pin (Wp) due to adding the weight W at location Xw is then:
Wp = W*Xw/Xp
This is a weight change, so the change Wp is added to the original pin weight to get the new pin weight.

Some things to notice are:
- When Xw = 0 (all the weight is over the axles), Wp = 0. This makes sense, all the load is carried over the axles.
- When Xw = Xp (all the weight is at the pin), Wp = W This also makes sense, all the weight is being carried at the pin.
- For a toyhauler, Xp is often negative since the weight is in the garage behind the axles. This leads to the pin weight being reduced by adding garage weight.
- W can be negative, so the same formula can be used to show the impact of removing weight as well as adding weight.
- W can be due to cargo changes or fluid changes.
The formula can be also used for multiple weight changes at once by adding each Wp, so changing weights and fluid levels can be put into a spreadsheet if desired.

It's simple force times distance equals force times distance. So the new load times the distance from the pin to the wheels should equal the added load in the rear times the distance to the wheels.

[BobKilmer]

It's simple force times distance equals force times distance. So the new load times the distance from the pin to the wheels should equal the added load in the rear times the distance to the wheels.

That is what the equation says in my post. It is written so the pin weight can easily be computed.