# Calculating Tongue Weight

Question asked by Stephen Bittner on Dec 19, 2018
Latest reply on Jan 7, 2019 by Jim Steinmeyer

I’m trying to determine tongue weight using my 3D model. I’m manufacturing a model of a vehicle, and the vehicle is actually the trailer as well. The model/trailer has two axles mounted in the typical locations you'd expect to see them on any given trailer. Here’s what I know:

1. Total mass of the trailer (with and without the axles, tires, and wheels)
2. Center of mass of the vehicle
3. Distance of the hitch to the center mass
4. Distance of the center of mass to the center-line of the dual axles.

Use SW to check where the CG is of your trailer and any load on it. If the CG is in front of the axle centerline, then the force on the tongue will be the percentage of that load that the CG is in front of the axle vs. the distance from the axle to the hitch ball. For example, if the distance from the ball to the axle is 50" and the CG is 10" in front of the axle, and the mass of the trailer is 1000#, then the tongue load will be (10/50)*1000, which is 200#.

My question: Should I include the mass of the two axles and tires/wheels in the calculation? (Ignore the front axle in my image, as this axle is not load bearing and will be lifted out of the way during tow mode. The only load bearing axles are the two axles toward the rear.)

I’m thinking that the axles/tires/wheels don’t actually apply any load, and that only the masses above the axles/tires/wheels would apply to the calculation. Any thoughts?

Likewise, am I making the correct assumption to use the center-line distance between the two axles in the formula that Wayne provided? It seems like a no-brainer, but I wanted to get some input from this well respected community.