Archived Trailer Guys Questions
The Boat Trailering Guys
I thought your response to the question of how to measure the tongue weight of a trailer lacked some creativity (February 2004). The best way I know is to use the spring rate of the tow vehicle`s rear suspension as a guide. It is not as accurate as a scale, but to get to a range of 5-10% of your boat and trailer weight it is more than accurate enough. You do this by measuring the distance of travel the hitch makes as a weight is put on it. First measure a point on the hitch to the ground with no added weight. Then measure those same points when a known weight is put on the hitch. (I use a person to stand on it). Then take the known weight and divide it by the difference of the two measurements. This gives you the spring rate lbs/inches of travel. Simply measure the distance of travel the trailer gives the hitch, and you can figure its weight.
P. Klinefelter, Richmond VA
Answered on: 6/2005
MIKE: There is a very reliable and accurate method of determining tongue weight of a trailer and that is the scale method that I have mentioned in the past. I am not familiar with the variables that can affect the spring rate of a vehicle. Will the spring rate be the same at 100 lbs or 500 lbs? Will the age or wear of springs affect the spring rate at variable weights? Your method will probably get you close enough, but it has not convinced me to give up the tried and true scale method. For those who missed the scale method, here it is: Tongue weight should be around 7-8% of your total trailer weight with load. Given that percentage, most bathroom scales read up to 300 pounds, which would allow you to come up with tongue weight of a total load of approximately 4,000 pounds, by resting the tongue directly on the scale. If the total weight is greater than that you can do the following procedure: Take a 4' piece of 2x4, set one end on a block of wood and the other end on the scale. The distance between the scale and block (center to center) is 3 feet. Place a spacer, such as a pencil, between the 2x4 and the block and also at the other end between the 2x4 and the scale. The 2x4 is actually resting on the pencil. -Rest the trailer tongue on the 2x4 1 from the end with the block (measure from the pencil to the center of the coupler), and 2 feet from the scale (center to center). -To obtain the tongue weight, multiply the reading on the scale by the number of feet between the pencils. In this case it would be a multiplier of 3. Make sure that you do this on a flat surface with adequate support under the scale. Either a paved surface or a piece of plywood will give enough support.
The Boat Trailering Guys: Mike