Calculating how an extension de-rates your receiver.

[mkirsch]

How would you go about calculating how much a receiver should be de-rated with a 14" extension?

Secondarily, does anybody know what a Curt 24" receiver tube is rated for?

http://www.curtmfg.com/part/49240

That's what I used to make my extension. It is cross-drilled to provide 14" of extension, and extends through the receiver box on my truck's Reese Titan.

[bjbear]

mkirsch wrote:
How would you go about calculating how much a receiver should be de-rated with a 14" extension?

Secondarily, does anybody know what a Curt 24" receiver tube is rated for?

http://www.curtmfg.com/part/49240

That's what I used to make my extension. It is cross-drilled to provide 14" of extension, and extends through the receiver box on my truck's Reese Titan.

As This question comes up frequently, I thought I would take some time and share some knowledge for what it is worth.........

mkirsh asked 2 questions.....

1. How much would a 14" extension de-rate his stock receiver - The chart previously posted can answer this. To use the chart, you need to determine what the distance is going to be from the rear mounting bolts/weld of the receiver to the center of the ball. Without knowing exactly how he is going to build this, I am assuming that he will have 14" of extension plus 11" added by his ball mount for a total of 25". Using the chart, if he has a Reese Titan Class V receiver rated at 1200 lbs (1700 with WD), then using the 14" extension, it should be de-rated to 530 lbs. If using a properly set up weight distribution hitch, the rating will increase to 750 lbs.

2. If he used the Curt extension, what will be the revised rating if it is cut down to 14" - Using the info for the Curt 24" to 34" extension which should be the same material and manufacturing process, you can back calculate (reverse engineer) the revised rating. I estimate that it will be Max tongue weight 900 lbs. Using a weight distribution hitch, that rating will increase to 1200 lbs.

One of the problems with estimating the strength of a home made extension, is that there are too many variables to build a standard calculator. You need to know the type of metal, the manufacturing process and the fabrication process to calculate the strength. There are also several assumptions such as the safety factor to use and the calculation of dynamic loading. That is why there is no mention of the extension in the on-line calculator. It is assumed that a manufactured extension with a known rating will be used. mkirsh is smart to use a manufactured extension and cut it down. That way, you can use the manufacturers ratings as a basis as they have control of the type of material and the fabrication.

Lastly, as others have mentioned, you also need to consider the added load a trailer on an extension will add to your rear axle - This is where the previously mentioned on-line calculator can help. It allows you to enter the various measurements that are needed and performs the calculation, giving you a reasonably accurate answer.

Hope this helps. It is not offered as an engineered solution, just my understanding based on many years working in the engineering field.

[billtex]

mkirsch wrote:

billtex wrote:

mkirsch wrote:
billtex,

That link does NOT calculate or show how much the receiver is derated. It simply tells me how much weight is where on the truck.

Where do you get your information on how much the tube is rated for?

Scroll down...

The rating came off the Curt website.

Bill

I've scrolled all the way to the bottom. I still see no calculator. Unless you're talking about the chart, which was posted on page 1 of the thread.

Where on the Curt website?

This is what I have:

http://www.curtmfg.com/part/49240

No ratings anywhere on that page.

I believe this is for the exact tube you showed above, from Curt website;

2” x 2” receiver tube and features a collared opening for added strength. It has a gross tow weight of 5,000 lbs. and a tongue weight capacity of 500 lbs., making it a useful towing option for many small to medium size trailers. The CURT hitch box comes with a hole for inserting a hitch pin and clip and can accept any ball mount or hitch-mounted accessory with a 2” x 2” shank.

You will need to do some work for the load specific to your application; tongue weight, length of fulcrum, etc to determine the exact load.
Either that or purchase a Torklift extension that is rated for a specific load.

[mkirsch]

billtex wrote:

mkirsch wrote:
billtex,

That link does NOT calculate or show how much the receiver is derated. It simply tells me how much weight is where on the truck.

Where do you get your information on how much the tube is rated for?

Scroll down...

The rating came off the Curt website.

Bill

I've scrolled all the way to the bottom. I still see no calculator. Unless you're talking about the chart, which was posted on page 1 of the thread.

Where on the Curt website?

This is what I have:

http://www.curtmfg.com/part/49240

No ratings anywhere on that page.

[noteven]

bjbear wrote:

ticki2 wrote:
From TCU http://www.visualsc.com/hitch_calc.htm

The rule of thumb I use is:
Revised Receiver Rating = (11 / (11 + EL)) * Mfg Rating
Where EL = the length of your extension in inches & Mfg Rating = the published rating for your receiver.

So assuming you would put a regular ball & mount in your 14" extension, you would derate your receiver to 44% of whatever the rating is from the manufacturer.

Or you can use this chart.

Assume your 14" extension will give a total extension of 25" when the ball/mount is added.

Chart on page one of this thread...

[billtex]

mkirsch wrote:

billtex wrote:
All this mental masturbation, while entertaining, does not answer the OP’s question. Find your answer
here based on the specifics of your loads, wheelbase, etc.
Curt rates that tube at 5,000 lbs.tow capacity and a tongue weight capacity of 500 lbs.
Hope this helps.

billtex,

That link does NOT calculate or show how much the receiver is derated. It simply tells me how much weight is where on the truck.

Where do you get your information on how much the tube is rated for?

Scroll down...

The rating came off the Curt website.

Bill

[Kayteg1]

Than... maybe you can do without extension

[ticki2]

This may help .
http://sketchup.engineeringtoolbox.com/square-hollow-strucural-sections-hss-c_79.html

[mkirsch]

billtex wrote:
All this mental masturbation, while entertaining, does not answer the OP’s question. Find your answer
here based on the specifics of your loads, wheelbase, etc.
Curt rates that tube at 5,000 lbs.tow capacity and a tongue weight capacity of 500 lbs.
Hope this helps.

billtex,

That link does NOT calculate or show how much the receiver is derated. It simply tells me how much weight is where on the truck.

Where do you get your information on how much the tube is rated for?

[Kayteg1]

Reddog1 wrote:

Kayteg1 wrote:
... Add truck own rear axle weight (around 3000lb ?), so what is the total? ...

I really appreciate your response. No need, that I am aware of, to be coy. Being clear certainly helps for credibility. To answer a question with a question is not very clear to me.

Using the info you provided, what effect does a Weight Distribution hitch have?

I ask these questions because I am interested in factual data as to how extensions and trailers can impact our camping experience.

Wayne

EDIT: My wheelbase is 160 inches. My TC is 4200 pounds. My truck is about 7,200 pounds.

I did measure my wheel base at 13' (just with tape) so sounds like we have similar duallies although mine is over 9000 lb.
With duallies usually you don't have to worry about rear axle load, but since I put my camper with some distance behind the cabin, I am planning to stop at the scales at some point.
Weighting is highly advisable when you plan to tow.
Weight distribution is compensating for cantilever effect, but all comes with limits and putting 700 lb tension springs on long hitch extension sure brings some reliability concerns.
mkirsch got the point, so hopefully more will understand that strong extension is just the beginning of the questions you suppose to have.

[billtex]

All this mental masturbation, while entertaining, does not answer the OP’s question. Find your answer
here based on the specifics of your loads, wheelbase, etc.
Curt rates that tube at 5,000 lbs.tow capacity and a tongue weight capacity of 500 lbs.
Hope this helps.

[mkirsch]

A weight distribution hitch would be akin to an adult lifting up on the right end of the teeter-totter in the picture above.

Oh, and Kayteg1's math works out to 6400lbs. My RAWR is 9350lbs. I could load another modest hardside TC on top of the one I already have and still not overload the axle.

My extension is only 14". Not 4'. So 700lbs would only add about 1000lbs to the rear axle. I wouldn't even need weight distribution at that point.

This is an awesome thought exercise guys. Thanks!

[Reddog1]

Kayteg1 wrote:
... Add truck own rear axle weight (around 3000lb ?), so what is the total? ...

I really appreciate your response. No need, that I am aware of, to be coy. Being clear certainly helps for credibility. To answer a question with a question is not very clear to me.

Using the info you provided, what effect does a Weight Distribution hitch have?

I ask these questions because I am interested in factual data as to how extensions and trailers can impact our camping experience.

Wayne

EDIT: My wheelbase is 160 inches. My TC is 4200 pounds. My truck is about 7,200 pounds.

[Kayteg1]

That was long time ago, but from my memory it was 5th grade physics how the lever works.
I know the "hands on experience" guys don't remember much of the school, so let me make quick sample.
Mine F350 is long wheel base, but my guesstimate for long bed, short cab F250/350 the wheelbase is about 9', while the standard hitch come with the ball 5' behind rear axle.
So simple sample with 4' extension will make the trailer ball 9' behind rear axle, what in this sample will equal to the distance from rear axle to front axle.
So having 1:1:1 lever the tongue weight will take equal weight off front axle, meaning the rear axle will carry both - the tongue and cantilever weight.
The 700lb tongue weight will add 1400 lb to the rear axle.
Add that close to 100% of camper weight will go on the rear axle, makes 3400lb.
Add truck own rear axle weight (around 3000lb ?), so what is the total?

[noteven]

Reddog1 - I'll have a go at the math:

The tongue weight transferred to the rear axle of the tow vehicle with an extension?

Ans: All of it. ?