GVWR Sticker and Alterations Debate!

[drfife]

You guys could argue how many angels can dance on the head of a pin.

How many here can honestly say they have never exceed any vehicle ratings for a trailer, tow vehicle or motorhome? Unknowingly is not an excuse.

[JohnBoyToo]

The basis of your statement is incorrect...

EVERYONE knows angels don't dance !!!!!!!!!!!!!!!!!!!!!!

GOSH, what we have to put up with in a public forum

[BFlinn181]

http://www.irv2.com/forums/attachmen...1&d=1347399616

It's not the pulling, it's the stopping!

[3665RE]

Rusty

You missed the point all together.

We were not testing an engine.

We were testing a truss.

We were not testing the yield.

We were establishing the safety margin was 50% without yield.

The frame of your trailer and TV are a truss of some type.

The fatigue analyses was previously determined in previous certifications. Not an issue for the modification.

The 1% is not a yield.

The 1% is considered the normal set a truss would take until it is subjected to it normal static load. The static load is opposite the test load. When the wing was turned right side up and mounted there was 0% deflection.

As I see it there is a very close correlation between the truss used in the wing of an aircraft and a building, bridge, trailer, RV or truck. It is the same engineering principal.

The object of the test was to determine the safety factor. The test determined the truss could sustain a 50% overload with out permanent damage.

There is not any consideration for repeated overloads of this magnitude. The overload the fatigue analyses are conducted use a constant 20% overload.

As far as I am concerned a truss is a truss regardless of whether it is in your RV or the roof of your house.

I don’t think there is a 100% safety factor in the structure of your RV or TV. Maybe a 100% yield.

The load capacities are based on a lot more items than just the trusses in the vehicle.

3665RE

[RustyJC]

Originally Posted by 3665RE

The 1% is not a yield.

The 1% is considered the normal set a truss would take until it is subjected to it normal static load. The static load is opposite the test load. When the wing was turned right side up and mounted there was 0% deflection.

With all respect, that's not what you initially said. You said:

Originally Posted by 3665RE

The test to determine a major modification to an aircraft like extending the winds 3 ft. is 150% of the design load factor without any deflection in structure that doesn’t return to with 1 % of its original shape.

If the material is stressed to the point that it doesn't return to its initial dimensions, it has by definition yielded - the stress has exceeded the material's yield strength.

The Materials Science definition of yield is:

Definition: The Yield Point can be defined as the point where a tensile test piece begins to extend permanently. If the load is reduced to zero, the test piece will not return to its original length.

In the case of a bending load, when yield occurs, the tensile strength of the material has been exceeded at the point/plane of maximum surface stress, and permanent deformation has occurred.

Let's not hang up the thread on this point of discussion, however. The important point, IMHO, is that the end user of an RV, receiver hitch, etc. doesn't know what safety factors have been used in the design, doesn't know what testing has been performed to confirm strength and fatigue resistance of a design, and therefore is treading on thin ice when assuming how much safety factor exists that he/she can eat into with higher-than-design loads. The fact of the matter is that OEM receiver hitches have failed at or below the published tongue load and towed load limits of the hitch due to defective welds, bolting attachment, etc., so one could be operating with a hitch that has a SF of less than 1!

Rusty

[Route 66]

As Rusty notes above, let's get back on topic and away from the unrelated technical aspects.

Thanks!

[3665RE]

Hi

I hardly see that discussing the structural strength of the complements when considering operating in an over weight condition not on subject.

3665R

[3665RE]

OK here is the way the Federal regulations work.

Here are 2 examples.

The feds claimed to not control by regulation the following items.

The height of vehicles operating on the Federal Highway system.

The use of child restraint seats.

Ok now the states get their money for building and maintaining the Federal Highway system from the Federal government.

This money comes to them thru “Grants”.

All grants have a paragraph or several paragraphs titled “Grant Qualifications”.

So while the Federal Government will tell you in writing that they “don’t regulate vehicle heights and use of child restraint seats” what they do is require the states to enact rules, regulations or laws to regulate these items on a state level before they can qualify for the grant money.

In 1966 (may be incorrect on the year but close) the grant qualification was to enact a rule, regulation or law to regulate the height of vehicles to 13ft 6 Inc. on the federal highway system.

To days grant qualification requires states to enact a law to require the use of child restraint seats before they can qualify for the money.

So in reality the statement by the Federal Government that they don’t regulate the change of DVWR is only correct if you are sure that some time in the past a grant qualification didn’t require the states to enact a rule, regulation or law to enforce those requirements on the individual.

These can be in some odd locations. The one example I can think of rite away is in Florida. The regulation limiting non-commercial vehicles to a 2-vehicle tow (TV & 1 trailer) is contained in the commercial vehicle regulations concerning the double trailer tow. It is done in a single line that states tandem trailer tow is not applicable to non-commercial vehicles.

3665RE

[elkhornsun]

Commercial trucks are regulated as to the weight per axle to minimize damage to the roads. 99% of the wear and tear on the highways is from trucks under the legal limit though the trucking industry lobbies to keep increasing the maximum allowed weights. This is not rocket science and anyone who has driven down the highways can see the difference in wear on the right versus the left lane on an interstate or see where trucks are returning to a plant empty and which side of the highway they are using when carrying a load.

Vehicles leave the factory with a manufacturer's weight ratings based on the configuration of the vehicle when it left the plant. The weight capacity is based on the limiting factor which is usually the tires. It is seldom the axle or suspension or drive train components. My truck has a rear axle rating from GM of 6700 lbs. but the manufacturer of the axle is AAM and they rate the axle at 11,100 lbs. which is quite a bit more.

The stock tires that came on the truck had a load rating by Firestone of 6400 lbs. which is greater than the 6000 lb. rating of the standard axle provided by GM with these trucks. The same truck with a dually axle is rated 4,000 lbs. higher and it is the same axle and wheel bearings and differential but has the load supported by twice as many wheels. An owner can also greatly increase the load capacity at the rear axle with a SRW truck by using 19.5 rims and tires.

In the 1960's when offroad driving became popular in the USA there were many shops and businesses (like Rhino and Rancho and Cepek) that sprung up to strengthen the trucks rims, tires, shocks, and axles, which were not designed for the loads encountered off the pavement. It was unusual not to see trucks with offroad tires that did not have new rims and an axle truss and double shock mounts. It seems very strange that 40 years later that there are those who think that a factory weight rating is sacrosanct and unchangeable.

Changes to the stock rig, even by virtue of age and use, can alter the safe load capacity of a vehicle for the better or the worse. When some people form an organization and seem official and do a "study" that may or may not be done in a proper manner and then make a statement that 56% of the RV's are overloaded this really tells me absolutely nothing.

To be an accurate study these people would need to take a random sampling of all RV's in use and have all of them weighed and all of them evaluated by an engineer as to the load capacities of each. I would bet my life that they did not do this.

For the average person it is a matter of weighing the RV when new at a CAT scale and comparing that to the manufacturer's specs and then loading the RV for a trip and weighing it again. If the gross weight per the manufacturer is 15,000 lbs. and the owner has not modified anything and the vehicle is new and the RV when loaded weighs in at 14,999 lbs. then it is not overloaded. The stopping distance of the RV at its "wet" weight may be 20% greater than when empty but that is something different though usually overlooked. The fully loaded RV may not be over its allowed weight but it may nonetheless be unsafe to operate as the people driving the Ford Explorers with the Bridgestone tires learned much too late.

It is only in the last couple of years that the SAE (society of automotive engineers) produced the new J2809 test protocol that tries to address this problem by having vehicles tested with their intended loads. If a truck has a grew cab and is rated to tow 20,000 lbs. then its acceleration, grade control and engine braking, and stopping distance should be measured with this load in place and 600 lbs. in the cab and not an empty truck with only the driver in the cab.

[TopV]

I just bought the trailer that fits the truck. Isnt that how it works?