Towing a travel trailer weight calculator

[cpaharley2008]

I thought this was unique:
Travel Trailer Weight Calculator

[thoer]

Originally Posted by cpaharley2008

I thought this was unique:
Travel Trailer Weight Calculator

Nice find Jim - thanks!

[fudge_brownie]

I tried it out with as many numbers as I had available for my vehicle and tow. I was disappointed with the results, it just seemed to apply my desired safety margin and give me the same numbers back.

[Brian B-P]

Originally Posted by fudge_brownie

I tried it out with as many numbers as I had available for my vehicle and tow. I was disappointed with the results, it just seemed to apply my desired safety margin and give me the same numbers back.

Yes, it will do that if you don't have many of the values, or if for any other reason the vehicle appears to be capable of towing the full listed trailer weight capacity. On the other hand, it will catch situations such as GCWR limiting someone who is carrying bunch of cargo or passengers in the tug... if they remember to include that cargo and those passengers in the GVW.

[Brian B-P]

Thanks Jim. It is an interesting tool, and has some nice features, such as the ability to enter each value in whichever units you have, and the ability to check whatever portion of the data you have.

It would be nice if it let you enter weights of passengers, cargo, and the vehicle itself separately.

My biggest concern is that by not including some important data, some issues cannot be caught. For instance: it doesn't include wheelbase or overhang to the hitch ball, or axle loads, so it can't check for an overloaded rear axle. With what it handles, the GAWRs are useless except as a poor substitute for a missing GVWR. It is very easy to overload the rear axle even though the total weight is okay; my concern is that someone in this situation will not know about the problem, and since they filled in every blank they might be reassured and stop checking.

Fundamentally, it only adds and subtracts weights and their limits, and does nothing with weight distribution. I use a spreadsheet to check those issues - the math isn't hard.

Within its limits, it's a handy tool.

[TAfraser]

Brian, I've been wrestling with this issue. I've played with the calculator in the first post and found it very interesting. While I can give it most all the numbers it asks for, including the actual vehicle weight, I couldn't give it the actual rear axle weight. The best I could do was use the weight distribution ratio given by the manufacturer (rough at best). With using a 12% tongue weight to trailer weight and applying the 500 lb hitch restriction, I can only tow a 4167 lb trailer (0% safety margin). Applying a 10% safety margin lowers that number to 3750 lbs. Since I just purchased a 21, I'm very concerned. I have to believe that the vehicle manufacturer applies it's own safety margins when supplying it's tow and hitch ratings. Since we don't know what those safety margins are, is that the reason we add more, or is it that we just don't trust the manufacturer to do his part properly?
It sounds like your spreadsheet takes other safety issues into account. Care to share?

Tom

[cpaharley2008]

Tom, you do not mention your tow vehicle?

[TAfraser]

I'm towing with a Honda Ridgeline. It has a tow rating of 5000 lbs with a tongue rating of 500 lbs. There's more to be considered, but that has to do with elevation calculations. I towed the 21 from Escape to Auburn Washington, not using a weight distribution hitch, without issues. In fact, it sat better (level) then our 17' Casita did. It felt very stable even in side winds. I know Escape recommends a minimum tow rating of 5000 lbs for the 21, but looking at the numbers, I wonder if that's really enough.
Tom

[cpaharley2008]

If you hitch says 5000/500 then you will be okay. The 21' has a max of 4500# on the specs. I'm wondering now about my FJ, using the above calculator says 4700 is the max for my FJ, although my hitch says 5000/500. I need the Andersen for the FJ, it squats too much. My Hemi Ram is fine without the Andersen. Will need to wait and see.

[Brian B-P]

Originally Posted by cpaharley2008

If you hitch says 5000/500 then you will be okay. The 21' has a max of 4500# on the specs. I'm wondering now about my FJ, using the above calculator says 4700 is the max for my FJ, although my hitch says 5000/500.

The hitch ratings are two of the several limits, but have nothing to do with the vehicle's capacity. Since 5000 pounds is the limit for Class 3, hitches commonly have that rating... regardless of what the vehicle can handle. 500 pounds is commonly the hitch weight limit for a Class 3 hitch in weight-carrying mode, but again that has nothing to do with what the vehicle can actually handle.

[Brian B-P]

Originally Posted by TAfraser

I have to believe that the vehicle manufacturer applies it's own safety margins when supplying it's tow and hitch ratings. Since we don't know what those safety margins are, is that the reason we add more, or is it that we just don't trust the manufacturer to do his part properly?

I think those are both essentially the same reason, and I suppose that is why some people add more margin. I think others add a margin because they are checking only the trailer weight limit (not GCWR, GAWR, GVWR...) and so they "want to be safe" without doing the work. Of course, they might just have a vehicle from a less trustworthy manufacturer...

Originally Posted by TAfraser

It sounds like your spreadsheet takes other safety issues into account. Care to share?

All I added is the distribution of load between the front and rear axles of the tug, and I don't have the cool "supply what you have" feature.

I have no idea how well this will work for others, but try this link to Google Drive and you can see my workbook of four spreadsheets: two for different configurations of someone's minivan and trailer, one showing scale readings and working out the pin position of Fran and Dave's Frontier/Escape rig, and one for Fran and Dave's rig. To play with it yourself, you could copy the desired sheet to your own Google Drive spreadsheet.

I have attached a PDF (readable) version of the workbook to this post; unfortunately, Excel files are not allowed as attachments, so no formulas (but they're visible in the Google Drive spreadsheet document).

[TAfraser]

My hitch indicates 5000/500, and the Ridgeline is rated for 5000 lb of towing. The placard on the side of my 21 indicates a GVWR of 2090KG, which is 4607 lbs. Using 4500 lbs, the tongue weight (at 12% of trailer weight) would be 540 lbs, exceeding the hitch rating. Turning this around, applying the 12% rule to the hitch maximum gives me a towing capability of 4167 lbs. This time I'm below what the trailer will probably weigh when fully loaded. All these numbers are without applying the so called safety factor. Hopefully the manufactures apply an appropriate safety factor when publishing their numbers. BUT, after working in Metrology (calibrations of test equipment) for 26 years, manufacturers are more interested in sales then safety when advertising.

[TAfraser]

Nice job with the spreadsheet Brian. Thank you

[cpaharley2008]

Tom,
Do you have a Sherline t/w scale? that may help with your numbers.

[Brian B-P]

Originally Posted by TAfraser

Nice job with the spreadsheet Brian. Thank you

You're welcome!

I was half-expecting something more like "what is that chicken scratch supposed to mean". Questions and comments are welcome, although if detailed might be best by e-mail (my address is registered with the forum).

[Brian B-P]

Originally Posted by TAfraser

Using 4500 lbs, the tongue weight (at 12% of trailer weight) would be 540 lbs, exceeding the hitch rating. Turning this around, applying the 12% rule to the hitch maximum gives me a towing capability of 4167 lbs. This time I'm below what the trailer will probably weigh when fully loaded.

That makes sense. Some options:

1. reduce trailer weight (carry less stuff)
2. use lower tongue weight fraction (with suitable distribution, 12% should not be necessary; tow vehicle manufacturers usually assume 10%)
3. check if the Ridgeline allows a higher tongue weight if a weight-distribution system is used (commonly true for other vehicles, especially pickup trucks)

Since the online calculator ignores weight distribution, it ignores weight-distributing hitch (WDH) systems. My spreadsheet ignores WDH as well.

Originally Posted by TAfraser

... manufacturers are more interested in sales then safety when advertising.

In some cases (especially the "Big 3" pickup manufacturers") that seems to be true, but I think the advertised numbers are more misleading by omission (of all the other limits) than by exaggeration (of the basic trailer weight limit).

[TAfraser]

Honda recommends against the use of weight distribution hitches. Their only reason is that if the hitch is adjusted wrong it becomes a safety issue. I've called them about it and can't get a better explanation. I've checked with a Reece hitch installation vendor and they also couldn't answer the question. They actually install weight distribution hitches on Ridgelines. There are many on the road using WDHs with great success, and of course, many that warn against their use. I'm getting dizzy just typing about it, but Honda's recommendation is the reason I checked with Anderson about the weight necessary for the sway to be effective. I can use very little weight distribution (100 lbs) and still get the advantages of sway control.

[Brian B-P]

Originally Posted by TAfraser

Honda recommends against the use of weight distribution hitches. Their only reason is that if the hitch is adjusted wrong it becomes a safety issue. I've called them about it and can't get a better explanation.

That's enough for me. Personally, I would just keep the tongue weight down to 500 pounds, but a properly adjusted WDH is fine, too.

Originally Posted by TAfraser

... I checked with Anderson about the weight necessary for the sway to be effective. I can use very little weight distribution (100 lbs) and still get the advantages of sway control.

I agree - some WD designs, especially the Anderson No-Sway, would need very little WD action to exert substantial sway control.

[cpaharley2008]

Yes, but remember, the heavier the tongue, the less sway probability.

[Brian B-P]

Originally Posted by cpaharley2008

Yes, but remember, the heavier the tongue, the less sway probability.

Yes, if everything else is equal. Tongue weight is not the only factor: a trailer with higher tongue weight will be no more stable if it also has mass distributed out at the ends (for instance - big batteries and generator on the tongue, cargo box on the back).

This is another of the many factors that a simple calculator or a fixed limit can't account for. Tow vehicle GCWR is normally based only on drivetrain reliability, and except possibly when tested according to SAE standard J2807, the trailer weight rating is based on GCWR, tongue weight, and sometimes a guess at the likely stability-limited capacity for some sort of assumed "typical" trailer.