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Old 01-25-2014, 03:04 PM   #1
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Default Trailer Weight Calculations & Load Estimator Utility

Check it out.

I built this handy tool for the trailer towing community. It consists of the following two utilities:


Weight Calculation utility:
Input your CAT or other truck scale measurement data and the utility will perform a number of meaningful weight calculations. This information is useful in measuring the "real" weights of your tow vehicle and trailer against the maximum limits of both vehicles. The tool will identify if you are over the manufactured specifications in any area and bring this to your attention.

Load Estimator utility:
Allows you to input information about a given trailer and estimate the amount of load required from the tow vehicle to support the trailer weight. Loads are projected in Tow Rating and Payload figures. Useful for trailer shopping to quickly determine if a prospective trailer fits your tow vehicle capabilities.

The tool is based in Microsoft Excel, but no need for any software on your computer as you can access the utility online via Microsoft Skydrive. You can input your data online and even download a copy for offline use (assuming you have Excel installed locally).


Here are a few screen shots of the utility in action:












Access the Trailer Weight Calculations & Load Estimator Utility here:
https://skydrive.live.com/embed?cid=...oadButton=True

EDIT: updated to version 4.0 to include corrections from comments originating in this thread.
PS: please contact me with any uncovered bugs or issues.
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Last edited by xcntrk; 01-29-2014 at 12:03 PM.
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Old 01-25-2014, 03:27 PM   #2
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Bookmarked the site.
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Old 01-26-2014, 09:29 AM   #3
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Thanks for the spreadsheet, it's very useful.

Checked your weight calculations against mine and we agree. Displaying the results in percentages puts everything in perspective. My 130# over-weight rear axle doesn't seem so bad when displayed as 103%.

But I would add the trailer's GAWR to your sheet. Think a lot of trailer tire blowouts are due to overloaded axles and tires. Could even add a tire rating based on size and pressure I suppose, but the trailer's GAWR is a lot easier for people to obtain.

As for the Load Estimator, I find it less useful. The real problem is estimating the Loaded Trailer's tongue weight ratio, and there is no easy way of doing that. It's usually just "by guess and by golly". EDIT: But in your example above, using 15% is good, conservative practice. Make it the default?
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New:2014 Timber Ridge 240RKS ~7500#Loaded ~1100#TongueW 10.0mpgUS
Old:2010 Trailmanor Elkmont24' ~4000#Loaded ~500#TongueW 12.5mpgUS

Last edited by brulaz; 01-26-2014 at 09:41 AM.
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Old 01-27-2014, 08:54 AM   #4
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Quote:
Originally Posted by brulaz View Post
I would add the trailer's GAWR to your sheet. Think a lot of trailer tire blowouts are due to overloaded axles and tires. Could even add a tire rating based on size and pressure I suppose, but the trailer's GAWR is a lot easier for people to obtain.
That's a good idea to add trailer GAWR, although I'm not sure most trailer owners would know that information. This is sort of already accomplished by putting in the trailer GVWR. But to your point, it would be great to capture the trailer tire rating and compare that against the loaded trailer weight. I'll mess around with it and explore adding this to the next version.



Quote:
Originally Posted by brulaz View Post
As for the Load Estimator, I find it less useful. The real problem is estimating the Loaded Trailer's tongue weight ratio, and there is no easy way of doing that. It's usually just "by guess and by golly". EDIT: But in your example above, using 15% is good, conservative practice. Make it the default?
Yeah this tool is targeting two different audiences. The "Weight Calculations" utility is geared towards the experienced towing user who already has truck scaled measured data for his TV and Trailer. In this example the user can plug in his raw scale data and the tools will calculate useful information. The second audience is the polar opposite, those who don't have an existing trailer or any scale data and are attempting to identify how much they can reasonably tow. For this crowd the "Load Estimator" can take some simple input and "estimate" the TV capabilities required to support the load. You can plug in some simple data about a prospective trailer, then compare the load figures against your payload rating (door sticker) and advertised tow rating for your model.


This is exactly the kind of input I'm looking for, thanks for taking the time to comment!
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Old 01-27-2014, 12:09 PM   #5
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For some manufacturers, it's best to get the info off the stickers on the trailer rather than the catalogue. There you can find the trailer's GAWR as well as GVWR, tire size and rating (C,D,E), as well as Cargo Carrying Capacity (CCC).

The *catalog* dry weights or CCC for some manufacturers don't include standard or required options like a/c and so on. For example a Lance 1985 we looked at had a CCC of 1051# on the yellow trailer sticker, but CCC was 1955# in the catalogue. That's a huge difference.

Maybe with your program you can encourage prospective buyers to look more closely at those trailer stickers.
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2011 FX2 SCab EcoB MaxTow 3.73diff ~2050#Payload LT245/75R17E RAS
New:2014 Timber Ridge 240RKS ~7500#Loaded ~1100#TongueW 10.0mpgUS
Old:2010 Trailmanor Elkmont24' ~4000#Loaded ~500#TongueW 12.5mpgUS
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Old 01-27-2014, 04:20 PM   #6
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The calculator looks good however I do not agree with the WD% changing your payload requirement. A WDH will change your rear axle weight but not decrease the total load on the TV.
Also with most RVs (except Toy Haulers) if you take the dry tongue weight and divide it by the dry trailer weight you get a very close (I would say with in +/-1%) "projected" tongue weight percentage. How the trailer is load, particularly in reference to it size and # of axles can have any effect on tongue weight. But most RV trailers loaded by the average user will stay very close to the calculated %. Toy haulers are designed and offset for heavy weight in the rear and for that reason the dry tongue to dry weight ration is usually well over 15% closer to 20%. So if you ask for the dry tongue # and the dry Trailer # you can provide the calculated tongue weight %. Ask for the GVWR for the trailer and your calculator could provide the user estimated upper and lower payload limits that would be transferred to the TV by a given trailer.
example
Dry Tongue: 1000lbs
dry trailer: 9000lbs
% tongue weight: 11%
GVWR trailer: 10500lbs
minimum Tongue weight or payload transfered to TV: 1000lbs (dry trailer)
Maximum Tongue weight or payload transfered to TV: 1155lbs (when loaded evenly/correctly)

With a number like 1155lbs and the user knows he has a 1400lb payload, 2 kids, wife and dog. He can make a very informed decision on whether he can or cannot safely tow given trailer.
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Old 01-27-2014, 05:40 PM   #7
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Hmmm, so my understanding is that WD actually removes tongue weight and redistributes to the trailer axles? Sounds like that's not the case however and instead a WD hitch uses leverage to force some percentage of the rear axle load to the front?

Looks like v3.0 is in order...
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Old 01-27-2014, 10:47 PM   #8
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Quote:
Originally Posted by xcntrk View Post
Hmmm, so my understanding is that WD actually removes tongue weight and redistributes to the trailer axles? Sounds like that's not the case however and instead a WD hitch uses leverage to force some percentage of the rear axle load to the front?

Looks like v3.0 is in order...
The WDH does both, moving weight to the trailer's axle and back to the truck's front axle.

So yes, the amount moved to the trailer axles is not counted against the truck's payload.

In my case 140# is moved off the truck to the trailer. Without the WDH, the tongue weight is 1130#. So your 10% seems reasonable.

And I haven't had much success using dry % tongue weight to predict wet % tongue weight. My current trailer is supposed to be 12% dry TW, but when loaded with batteries, propane and all my stuff in the pass-thru, it's weighs in at a bit over 15%.

Which was a surprise. I'm now looking for a WDH with 1200# bars, and ditching the 1000# bars.
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New:2014 Timber Ridge 240RKS ~7500#Loaded ~1100#TongueW 10.0mpgUS
Old:2010 Trailmanor Elkmont24' ~4000#Loaded ~500#TongueW 12.5mpgUS

Last edited by brulaz; 01-27-2014 at 10:51 PM.
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Old 01-28-2014, 11:01 AM   #9
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So from a calculation spreadsheet standpoint, I'm not sure how one could realistically estimate the amount of TW distributed using a WD hitch given these variables. Some tongue weight goes forward on the TV while some small percent goes back into the trailer axles.

Any suggestions on how to reflect the benefit of WD in a load estimate tool such as this?
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Old 01-28-2014, 01:53 PM   #10
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Quote:
Originally Posted by xcntrk View Post
So from a calculation spreadsheet standpoint, I'm not sure how one could realistically estimate the amount of TW distributed using a WD hitch given these variables. Some tongue weight goes forward on the TV while some small percent goes back into the trailer axles.

Any suggestions on how to reflect the benefit of WD in a load estimate tool such as this?
Over on RV.NET there's a sticky by Ron Gratz on how a WDH works. All the physics is there, but I think it woud be too much trouble for most people. You would need all the measurements of ball to axle distance, truck wheelbase, WDH bar length, and then it would all depend upon how tight the WDH bars were tightened up. His calculations assume the max force of the tension bars.

Easier just to use your rough 10% approx. It's conservative, and people can change it to 20% or whatever, if they want.

No point in getting too precise, especially since the estimate of % tongue weight is going to be so dicey anyway. Over-precision can give people false confidence in the estimates ...

EDIT: I see now that Ron Gratz over on RV.NET is suggesting that 20% is a good average estimate of the tongue weight transferred back to the axle. http://www.rv.net/forum/index.cfm/fu...2.cfm#27492302
He's been collecting data on WDH loadings over the years and knows what he's talking about.
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2011 FX2 SCab EcoB MaxTow 3.73diff ~2050#Payload LT245/75R17E RAS
New:2014 Timber Ridge 240RKS ~7500#Loaded ~1100#TongueW 10.0mpgUS
Old:2010 Trailmanor Elkmont24' ~4000#Loaded ~500#TongueW 12.5mpgUS

Last edited by brulaz; 01-28-2014 at 02:10 PM.
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Old 01-28-2014, 01:53 PM
 
 
 
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