Mathematics experts show me your talent in calculating trailer capacity.

[alsayyed]

I was debating with some friends regarding the trailer capacity weight I mean how much this could carry. My friend wants to build trailer with 2 axl. Each hub will handle up 2500lb so if he had to install 4 tires how much load he can place on the trailer. Is there any mathematics calculation regarding this issue because I do not know anything about weight calculation.
Do the thickness of the square tube or open channel has to be a factor.

[tomboysawyer]

Since the suspension will mount to the axles (and not directly to the hubs), YES, the wall thickness and size of your axle material is a factor.

[scsmith42]

Alsayed, to determine trailer capacity you usually take the lesser of the axle capacity or tire capacity, plus the amount of weight carried by the trailer tongue, and subtract the empty weight (tare) of the trailer.

As an example, if you build a trailer with 5000lb capacity axle's (2,500 per hub), yet only put tires that are rated at 1,900 lbs each on it, then your gross trailer capacity will be based up on the tire capacity (the lesser of the axle or tire ratings).  This would mean that even though your axle is rated for 5000 lbs, the two tires on that axle are only rated for 3,800 lbs.  Two axle's of tires would thus have a gross capacity rating of 7,600 lbs.

From this, you would add the amount of weight carried by the trailer tongue.  For tag-along trailers (attach to a ball on the tow vehicle rear bumper or under-bumper receiver hitch), this is usually 5% - 10% of the trailer capacity.  In this instance, that would be another 760 lbs.  So, your trailer now has a total capacity of 8560 lbs (7,600 + 760).

From this, you subtract the empty weight of the trailer.  Typically you would obtain this by weighing the empty trailer, or calculating the weight of all of the components.  This varies depending upon the length of your trailer and the size of the components.  Typically, a 16' deck trailer with a couple of 5000lb capacity axle's is going to weigh between 1,500 - 2000 lbs.  Using the higher number, if the trailer weighs 2000 lbs and your gross capacity is 8,560 lbs, then you can transport a load weighing up to 6,560 lbs (8,560 lbs gross capacity less 2000 lb empty trailer weight).

Generally speaking, you want to make sure that your axle's and tires have the highest capacity load ratings that you can afford (and also that make sense for the loads that you need to carry). 

Scott

[alsayyed]

Scott thank you very much i think you have answered my question and I started to get more clue very well. becuase i have placed big heavy log on the trailer today i think that log weights around maybe 1 to 2 tons if i am correct very heavy. I know my logosol saw mill will not handle that log tomorrow i will try to post the picture.
very nice and thank you for the information and the calcuation.

[rebocardo]

Okay,

take capacity of axle/hubs/axle

(say 2500 pounds x 4 = 10,000)

minus total trailer weight (say 2000 pounds)

minus safety factor (500)

is

10,000
  -2000
    -500
--------
7500 pound load

On a 16 foot long trailer, with green oak logs, you can pile about two feet high because of wasted space between logs.

(16 feet x 6 feet wide = 96 cubic feet x 75 pounds per cubic foot = 7200)

[jokers]

Okay,

take capacity of axle/hubs/axle

(say 2500 pounds x 4 = 10,000)

minus total trailer weight (say 2000 pounds)

minus safety factor (500)

is

10,000
  -2000
    -500
--------
7500 pound load

On a 16 foot long trailer, with green oak logs, you can pile about two feet high because of wasted space between logs.

(16 feet x 6 feet wide = 96 cubic feet x 75 pounds per cubic foot = 7200)

Rebocardo,

I`m assuming that what you are describing is a tandem axle trailer with two 5,000# axle assemblies(hubs, tube, springs, brakes, and mounting hardware) right? Keep in mind that you have to make sure that each of your 4 tires is also rated for a minimum of 2,500# load(special trailer service tires) to theoretically achieve the full rated capacity of the axle and that they are properly inflated and there is no cracking or other physical defect, and this wouldn`t provide any margin at all if one tire fails.

I`m also wondering where the 500# safety factor came from? I`m not confident that a 500# margin is necessarily sufficient for a loose stacked 7,200 payload as it would be for a payload of logs that when bound to the trailer comprise a stiffening and load supporting beam, see what I`m saying, the margin would be payload specific for example what would happen if a loose stacked load positioned(or shifted) behind the rear axle when you hit a bump or a pothole. The dynamic load is increased(mass x velocity) just in the simplist terms.

alsayyed,

without knowing the specifics of trailer construction and how it will be loaded I don`t think it`s possible for any of us to give you an accurate estimate of what the trailer will handle. Scott has provided a few thumb rules for commercially produced and inspected trailers built using typical assumptions and engineering formulae, be very cautious when applying these to the homebuilt trailer.

Always, always, always err on the side of conservatism when towing a trailer. God forbid that you should ever have a problem but atleast here in the US if you do a team of lawyers, engineers, and insurance adjusters will be analyzing every detail of your trailering mishap looking to fix the blame and liability squarely on your shoulders. i know this from experience and it almost never pays to build you own trailer for use on public access roadways.

[rebocardo]

> I`m assuming that what you are describing is a tandem axle trailer with two 5,000# axle assemblies

No, you are assuming that is what the person
that started the post is describing.

This is what the person asked

"Each hub will handle up 2500lb so if he had
to install 4 tires how much load he can place
on the trailer."

"Is there any mathematics calculation regarding this
issue because I do not know anything about weight calculation."

I gave him the mathematics calculation regarding the issue
and about how much wood/weight could be placed on the trailer.

Not advice about tire choices and loading, which wasn't asked.

> The dynamic load is increased(mass x velocity) just in the simplist terms.

Yea ... feel free to provide your own


"mathematics calculation regarding this issue"

yourself.

ALSAYYED

> Do the thickness of the square tube or open channel has to be a factor.

Assuming you are talking about the frame, if you check car trailers on E-Bay, you will see the most common platform material for 7500 pound car trailers is 5" or 6" channel with a 1/4" wall thickness. Example: E-Bay item # 330152170014.  This is because with heavy use and abuse, this size has been found to last the longest in car trailers. We have many trailer makers in the state where I live and almost all build their car trailers with this as a minimum and standard.

If you are talkng about axles, most of the axle stubs are designed for 3" x 1/4" round steel tube on the larger capacity spindles.

Dexter is considered an industry standard, so this site might be useful for you when designing a trailer and what to use

http://www.dexteraxle.com/

This site has free trailer plans, plus, you can order your trailer stuff from them

http://www.championtrailers.com/UTILITY_TRAILER_KITS.HTM

You can use the utility plans for laying out your trailer, but, build it like you would a car trailer, heavy duty.

6" x 3" x 1/4" channel or tubing for the frame. 3" to 4" x 1/4" square tube for the tongue. On the tongue, you should make sure the steel is ASM500 or to some spec. like that (structural steel). Most steel that size is by default in the USA. If buying used steel, get steel from pallet racks, most use structural steel of at least 3/16" wall tubing! Try to use at least 2"x3"x1/4" angle for cross members on 12-16" centers.

On my trailers, I like an an extra channel member of 6"x3" across the back (basically doubling the rear frame/bumper) because that is where most of the load is driving a car onto the trailer or loading a log.

It is not a bad idea to install trailer jacks near each corner to steady the trailer, especially side loading logs to take the strain off the axle and tires on that side where you are loading.

[rebocardo]

On the Dexter site, go to

Resource Library
     Trailer Axle Resources
          Trailer Design Considerations

http://i.b5z.net/i/u/1080235/f/Design_Considerations.pdf

[scsmith42]

John, that's some great info - thanks for sharing.

Scott

[jokers]

> I`m assuming that what you are describing is a tandem axle trailer with two 5,000# axle assemblies

No, you are assuming that is what the person
that started the post is describing.

This is what the person asked

"Each hub will handle up 2500lb so if he had
to install 4 tires how much load he can place
on the trailer."

"Is there any mathematics calculation regarding this
issue because I do not know anything about weight calculation."

I gave him the mathematics calculation regarding the issue
and about how much wood/weight could be placed on the trailer.

Not advice about tire choices and loading, which wasn't asked.

> The dynamic load is increased(mass x velocity) just in the simplist terms.

Yea ... feel free to provide your own


"mathematics calculation regarding this issue"

yourself.

Rebocardo,  I wasn`t picking on you, simply expounding on what you had stated in your descriptive reply to alsayyed.

I mentiond tires and whatnot because too many people don`t consider there to be a difference between car tires and trailer tires when infact automotive tires are lightweights compared to equipment trailer tires. I`m sure that you know this but based on the questions that alsayyed asked, I didn`t feel confident that he did.

Now in regard to the mathmatical computations involved in how much weight his trailer can safely carry, did you really give him the proper values? For all you know they are building the frame out of spare wooden pallets and it wouldn`t be safe to carry your arbitrary 500# safety margin.

I will do the mathmatic calculations for a given frame size or load capacity per area right here on the forum if you will but there is a good chance that one of us isn`t going to look so right.  ;D  :D

[alsayyed]

i thank you guys very much you done well in giving information. very valuable information. I am still reading. very nice I thank you again and God bless

alsayyed

[rebocardo]

>  will do the mathmatic calculations for a given frame size or
>  load capacity per area right here
> The dynamic load is increased(mass x velocity) just in the simplist terms.

Yea ... feel free to provide your own


"mathematics calculation regarding this issue"

yourself.