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Old 10-28-2013, 04:43 PM   #1
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Question GCVW and frame extensions.

Have been wondering how the manufacturers come up with the weight rating for the hitch and load when they weld extensions to the frame of the RV. I was a welder in my previous life and repaired hundreds, if not thousands of rusted and broken frames on cars, trucks and motorhomes. It was not that rare to have the extension pull off the back of an RV that was towing something, and in many cases I really did not think they were overloaded. Anyway, I was crawling around the bottom of our R-Vision the other day and saw that the extension on it was just butt welded with a small 1/4 inch plate kind of tacked to the inside of the C-channel rails. It has a 5000# tow rating, but the construction really didn't look that great to me. There were no cracks or signs of failure, but I still welded 2, 1/4 inch by 1 foot long plates on the outside of the rails and now I feel better. The question is, how do they come up with that rating when the construction is obviously a "weld it the best you can" senario. Just wondering.
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Old 10-28-2013, 05:14 PM   #2
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As for Winnebago, they work hand and hand with the chassis manufacture engineers, as far as I know. When we visited the FCCC factory in Gaffney, SC we were told that each and every chassis that came off the line was designed to the specs of the purchaser. Winnebago boasts about their chassis designs and how they work with the manufactures to get the correct setup for the model that is being built.
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Old 10-28-2013, 07:49 PM   #3
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Unfortunately, what the engineers envision and design for is sometimes not translated into what comes out the back door. When the "inspector" is the lowest paid new hire on the floor, or the guy ready for retirement next week, quality remains a word rather than a practice. With those conditions, it's sometimes a wonder that ANYTHING comes out the door that resembles the design drawings.
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Old 10-29-2013, 08:34 AM   #4
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Unfortunately, what the engineers envision and design for is sometimes not translated into what comes out the back door. When the "inspector" is the lowest paid new hire on the floor, or the guy ready for retirement next week, quality remains a word rather than a practice. With those conditions, it's sometimes a wonder that ANYTHING comes out the door that resembles the design drawings.
Amen brother! You must be a member of the choir. How many of us have had a problem with our rigs just to find out that it was assembled wrong. No mater how good a design is, if it can't be translated into a functioning part or unit it is all but useless.

I remember the days of tube radios and tvs. Emerson had some of the best engineers on the planet designing for them. When a design was prototyped, rumor has it that a team with dycks started clipping components out. The one that caused the radio or tv to fail was reinstalled and what was working was manufactured. Does this happen in RVs?
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Old 10-29-2013, 12:45 PM   #5
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Remember the hitch's 5,000 tow rating is not necessarly the tow rating of the RV, It is a bit like the pressure moulded in the tire.. It is a MAXIMUM, for the hitch receiver and cross member.. The RV's maximum can be quite a bit lower.
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Old 10-29-2013, 12:55 PM   #6
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Remember the hitch's 5,000 tow rating is not necessarly the tow rating of the RV, It is a bit like the pressure moulded in the tire.. It is a MAXIMUM, for the hitch receiver and cross member.. The RV's maximum can be quite a bit lower.
The tire pressure molded into an RV truck size tire is the MINIMUM pressure for the maximum weight the tire should ever have unlike a car tire where it is the maximum pressure the tire should have.
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Old 10-30-2013, 08:10 AM   #7
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Quote:
When we visited the FCCC factory in Gaffney, SC we were told that each and every chassis that came off the line was designed to the specs of the purchaser. Winnebago boasts about their chassis designs and how they work with the manufactures to get the correct setup for the model that is being built.
Yeah, but the original question was about frame extensions, which are added by the coach builder in their factory, not at FCCC (or Spartan). Extensions are used (most often on gas chassis) when the RV manufacturer tries to "make do" with a less expensive, short wheel base, chassis under a longer coach. It's a way to offer a lower price for a longer coach and the chassis work is driven strictly by low cost. The "engineering" is minimal, in my opinion.

A similar problem arises in low-priced trailers. The RV builder uses a fairly short frame and extends it for a longer RV, attaching bumpers and maybe even a trailer hitch to light duty extension members. OK as long as nothing stresses it too much.
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Old 10-30-2013, 01:47 PM   #8
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The tire pressure molded into an RV truck size tire is the MINIMUM pressure for the maximum weight the tire should ever have unlike a car tire where it is the maximum pressure the tire should have.
Just another moment on this rabbit trail please. I have never seen this explanation printed anywhere. The psi tire tables read what is needed per axle weight for the tire in question. On my sidewall it states MAX with values next to it. Are you positive you are correct? These are Michelin 22.5 rim size. 110 is the MAX psi according to the sidewall.
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Old 10-30-2013, 02:52 PM   #9
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Originally Posted by jerichorick View Post
Just another moment on this rabbit trail please. I have never seen this explanation printed anywhere. The psi tire tables read what is needed per axle weight for the tire in question. On my sidewall it states MAX with values next to it. Are you positive you are correct? These are Michelin 22.5 rim size. 110 is the MAX psi according to the sidewall.
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Old 10-31-2013, 08:56 AM   #10
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Yeah, but the original question was about frame extensions, which are added by the coach builder in their factory, not at FCCC (or Spartan). Extensions are used (most often on gas chassis) when the RV manufacturer tries to "make do" with a less expensive, short wheel base, chassis under a longer coach. It's a way to offer a lower price for a longer coach and the chassis work is driven strictly by low cost. The "engineering" is minimal, in my opinion.

A similar problem arises in low-priced trailers. The RV builder uses a fairly short frame and extends it for a longer RV, attaching bumpers and maybe even a trailer hitch to light duty extension members. OK as long as nothing stresses it too much.
I can only speak for Winnebago building on Freightliner. The Freightliner Custom Chassis is build according to what the RV manufacturer orders, true. But when at both factories we found that the chassis work was not skimped upon. And with the three Freightliner chassis coaches I have owned, the frame construction always seems strong.

Finding the sloppy work and adding those reinforcing plates seems like a good decision and a good safety assurance. Too bad the manufacture didn't consider the long run over reduced cost.
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Old 10-31-2013, 08:54 PM   #11
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in regards to the OP. i would imagine there is an engineering formula they use at the manufacturing facility. i have experience with extending commercial chassis's and altering the factory wheel base and cab to axle specifications for building home delivery oil trucks and home delivery propane trucks. we have to calculate the weight of the tank with chassis wheel base dimensions to calculate weight distribution on the front axle and so forth. we usually have to lengthen the rear frame on most applications to accommodate the ICC bumpers and rear decks. per dot regulations the ICC bumpers need to withstand a rear end collision with a truck of the equal size and not impact the tank mounted on the chassis. we had a mechanical engineer draft up a design so our bumper and frame rail extension would be legal.

i know we are comparing apples to oranges here but if i had to guess they must have some sort of equation that reduces the overall gvw by some percentage by how ever long the frame extensions are going to be. its a simple matter of leverage i would imagine. the longer the frame extensions the less capacity the gvw would be. i'm sure the gain some gvw weight back by moving the rear axle to rear some.

In the end i couldn't agree with you more about the shoddy work that goes into these r.v.'s. Being a truck builder/welder for 15 years i cannot believe some of the corners these manufactures cut and how bad some of the quality of work is. From electrical to fabrication the work just plane out sucks. in all my years i have seen what works and what doesn't work. any electrical connection/splice exposed to weather should be soldered and shrink wrapped to protect the connection from the elements to ensure a zero future failure. The frame rail extensions should be "fish plated" on both sides of the the frame rail and if the extensions are long enough they should also be adding an additional factory cross member and not just relying on the sorry excuse of a 4' square tube they use for an inner bumper. i've already repaired quite a few poor designs on some under carriage structures on some of my friends r.v.'s and tow behind campers.

in the end it really comes down to money. the less materials and labor they have to invest in the manufacturing process the more money they make at the expense of the customer. sorry if my rant got carried away but good choice in adding a little extra protection and piece of mind to the rear of your r.v.
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Old 10-31-2013, 09:36 PM   #12
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Hornet8118 and his firm is the kind of a guy you need extending frames or inspecting them. I've seen operations like he describes and they do GREAT work. Finding them can be a chore, but a day or so talking to people in the heavy truck repair business or body building/mounting business, spring fabrication, or drive line modification area will probably know where the RIGHT people are.
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Old 11-01-2013, 07:15 PM   #13
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Steve, that is a great writeup! Of the RV frames you have repaired would you please tell us who is the worst offender? It is always great to get input from someone who is really walking the talk today. Thank.
Rick
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Old 11-01-2013, 07:35 PM   #14
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One of the culprits that I am aware of was National. They stretched a P32 chassis to accept a 36ft. coach. Beefed up the front suspension with a buggy spring to help cary the load. One of the worst riding/ handling RVs I have ever driven.That was a Tropical.
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