Revision q below
Travel Trailer weight Calc7q xls file
Travel Trailer weight Calc7q xlsx file
David, would you mind explaining what the Fin, Lin, and Fout abbreviations mean in your weight calculation spreadsheet? What is the logic basis for your calculations of effect on hitch weight or rear axle weight?
I’m trying to create a simplified spreadsheet that takes inputs similar to this web site (http://www.visualsc.com/hitch_calc.htm) but makes the calculations transparent. That site’s owner was rather vague when asked what he used for formulae. Your spreadsheet does that but is far more complicated than most users want or could comprehend. If it can be generalized, it would be really powerful.
Thanks for your time.
On my spreadsheet I have drawings showing lever action about a fulcrum. Fin is the force input at a distance (Fin) from the fulcrum. Fout is the force out at a distance of Lout from the fulcrum.
The fulcrum points I used are: the travel trailer (TT) rear axle, the TT front axle, between the TT axles, the TT coupler, the rear axle on the tow vehicle (TV) and the front axle on the TV.
I made a lot of distance measurements on the TT from discrete load points to the relevant fulcrum points. I also made similar measurement on the TV. This will allow a person to see the effects of load positioning in the TT on tongue weight, weight on TT axles, weight on TV axles, load positioning in TV on TV axles without making a million trips to a CAT scale at a large truck stop.
After trying (I guessed at what size I needed) two sizes of WD hitches (which were undersized for my TT and TV combination) I finally started looking at what the manufactures of WD hitches recommend. I found that the manufactures of WD hitches at most only ask for the loaded weight on my TT, TT loaded tongue weight, load in the rear of the TV behind the rear axle; but they did not ask about any weight just forward of the rear axle in the TV. Using that information they estimate the size of WD is needed. I am sure they must have made some guesses about what extra weight a person might put in the TV forward of the rear axle.
I have spent my life being an electronic technician not a mechanical engineer. I consider my spreadsheet just another estimator. I believe my spreadsheet would be more accurate if my TT had only one axle. At my level of mechanical ability, having two axles confuses me. That is why I chose to have three different fulcrums around the TT axles and four sets of calculations for my dual axle TT (back axle, front axle and between the axles). That way I could observe the different results and narrow down my guess work somewhat. I communicated with another RVer on another forum about what to do if my TT had two axles. He suggested that using a fulcrum point halfway between the two axles should give good enough results. That is why I have some calculations using the midway point. If you are a mechanical engineer, you might be able to enlighten me as to what to do for dual axle TTs. I am hoping some mechanical design engineer will respond to my spreadsheet sheet and tell me how to handle a dual axle TT in my spreadsheet calculations.
By the way, I have uploaded another revision of my spreadsheet to my blog/website. I have added information about what fulcrum points I used in each set of calculations. I also made a note that I assumed that the added weight to the TT is distributed evenly between the two axles if the TT is level along the front to rear axis.
I have had fun making the spreadsheet; but in the final analysis after I get totally packed for my next camping trip, I will probably make at least two trips to weight my rig on a CAT scale to get the weight for the TT, TV rear axle weight and TV front axle weight.
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