Frame Strength, Who to Believe! The RV Sales Guy or the New Truck Dealer? Maybe Neither?

[rruff]

Or do none of the above, and beef up the rails first thing.

What does that entail?

 

[ripperj]

What does that entail?

More than most can deal with.

Unless you have an engineered design that’s properly implemented (things like the welds and heat treatment and stress relief)..it’s very like that the failure will just be elsewhere.

People do wing it and get lucky though


Sent from my iPhone using Tapatalk Pro

 

[ThundahBeagle]

I hear what you’re saying and completely understand the point you’re trying to make. Where I would differ from your argument though is, in the first place a doctor is considered to be more of an expert and thus is expected to know more and be more honest to his/her patients.

Secondly, and sadly, I think that the unfortunate truth is that none of us should really take the word of someone who’s trying to make a commission off of us. Salesman are just that… Salesman! In most situations, they shouldn’t be held to be, or pretend to be, experts in regards to the products or services they are trying to get us to buy from them.

People are now spending as much money to buy camping rig combos as they spent on buying new homes not too many years ago, but not fact checking their purchases as they would have with a home. As a real estate investor, I’ve always known that it was up to me to always do my own due diligence, and to dig deeply for accurate, important facts involving the properties I’m considering buying, because I also know that I cannot and should not rely on the self serving statements made to me by sellers or their agents.

This cautious approach should be used for many other purchase scenarios. And the more money one plans to spend/invest on a purchase, the more critically important it is for that person to do his own due diligence. In too many cases though, people are too hurried or lazy (or ???) to do this.

Through the years there have been innumerable unsuccessful lawsuits filed in our courts based on ‘misrepresentations’ made to buyers in the marketing statements coming from manufacturers and/or the oral/written claims emanating from the sellers of goods and services. The courts usually have looked at this issue from the perspective of whether it actually was reasonable for the buyer to rely on the advice or information given to him/her by the marketing or sales staff, and frequently have held it was not.

The history of fraud cases in business shows that the courts have given an enormous amount of leeway to sale people who make erroneous, exaggerated, or even completely false claims about the goods and services they are hawking. Outright “puffery” in the issuance of these claims has too often been protected.

So knowing all of this, it is extremely important for, and ultimately the duty of all buyers to do their own due diligence to determine whether a product or service actually does meet their needs or satisfies their intended use. It totally sucks that people will boldly lie to your face to try to separate you from your money…and get away with it, but that’s the way of the world and something intelligent people always keep in front of themselves when buying expensive or important items.

The doctrine of Caveat Emptor has been around for centuries and our understanding of it got even more clarified by English Common Law rulings in the 1800’s. Many scholars argue that this concept actually dates back to early Roman Civil Law. In any event, this basic rule of commerce certainly is nothing new.

Right? Caveat Emptor.

I walked into a Chevy dealer about 10 years ago looking at new trucks. I was talking with a salesman, lamenting the fact that it was all buttons now instead of levers and shifters. To test his knowledge and truth, I peered under the truck and said "wow, so they finally got rid of the ladder frames on these Avalanches and went unibody, huh?"

He said "yep. Its actually better that way"

I walked out

But someone who has no idea, would have no idea.

 

[rruff]

Unless you have an engineered design that’s properly implemented (things like the welds and heat treatment and stress relief)..it’s very like that the failure will just be elsewhere.

I can definitely see that with welding on heat treated steel. I was wondering if something could be built that bolts to a C-channel frame.

 

[RoyJ]

Where did you find that spec?

P.S. Wrecker frames are reinforced.

It's not a spec, just based on what 1-ton class wheel lifts are rated to carry (3k lbs at very minimum), and their typical distance from rear axle.

I've never seen a wrecker with chassis reinforced at that particular area - just behind the cab. Not saying never, just never seen one.

 

[RoyJ]

That wrecker also isn't a dually crew cab.

Makes zero difference from a frame bending perspective.

3k lbs load, 6' behind rear axle, axle is the fulcrum, bending moment is 18,000 lb-ft

 

[RoyJ]

Wreckers are also F550 Ram 5500, or F600s . I don't think I've ever seen one less than a 5500 series, no f450s, no ram 4500s. Maybe their are.

MY thoughts are, how the hell are camper companies making slide ins built for trucks that are obviously 3500 series trucks with beds (only F450 has a bed, all other 4500 series trucks are chassis cabs). that is that damn heavy.... Plus that big.. At that point, flat bed it on a 5500 or bigger..

The wrecker I posted was a GM 3500.

An Eagle Cap 1165 has a COG at 61.5", or just over 5' behind the cab. That's right on the axle. Even if you shift that back another foot, we're talking 6000 lb-ft of bending moment.

If a wrecker can take 18000 lb-ft of bending, day in day out, for years before needing a frame repair, what made the Ram break after 1 trip?

 

[DaveNay]

If a wrecker can take 18000 lb-ft of bending, day in day out, for years before needing a frame repair, what made the Ram break after 1 trip?

The fact that the wrecker probably has reinforced frame members exactly for this purpose.

 

[RoyJ]

Just a couple of observations:

1: Note where the lifting ram and primary hinge point are on that tow rig. Both are IFO the rear axle. The loading is well forward of the rear of the truck body not "hung off the rear".

Not to turn this into a physics thread, but that's not how forces act upon the frame. I can upload a free body diagram, but this is easier to explain:

If your theory is correct, then I can put an infinitely heavy object on that towtruck (say Cat D8) and it'll never flip, right? Because the hinge point is forward of the axle?

Obviously we know that's not true. Hinge and hydraulic cylinder locations make 0 difference in frame bending. They DO affect bending moment on the wheel lift itself.

What matters is your fulcrum (rear axle), COG of the load, and distance from COG to the rear axle. The camper would need a COG 3 feet behind the rear axle (impossible) to match the stress of a tow truck.

 

[RoyJ]

We dont know precisely where the Ram frame bent. But from looking at the picture, to me looks like bending primarily at the arched portion over its axel. Which is often a designed weak for crashworthiness. considerable weight of camper was loaded there plus whatever length of frame extending beyond spring hangers.
A wrecker is built on straight framerails which probably reinforced part of factory 'Wrecker Package' which rails end pretty much at the spring hanger.

I read on another forum it's the front camper tie-down, apparently welded onto the frame. Don't know for sure though.

I want to believe it's the axle arch as well, that's how the older Raptors and ZR2s bent. In that case the bed probably ripped off its mounts, as it remained straight in the photo

 

[WOODY2]

Dupe, sorry

 

[PirateMcGee]

Makes zero difference from a frame bending perspective.

3k lbs load, 6' behind rear axle, axle is the fulcrum, bending moment is 18,000 lb-ft

Statics vs dynamics and there's a lot more to the equation. Regardless, the frame on a wrecker is reinforced.

 

[rruff]

I read on another forum it's the front camper tie-down, apparently welded onto the frame. Don't know for sure though.
I want to believe it's the axle arch as well, that's how the older Raptors and ZR2s bent. In that case the bed probably ripped off its mounts, as it remained straight in the photo

Looks like right behind the cab to me. If the tiedowns are welded on that would have negated the heat treating, locally anyway.

 

[calicamper]

The wrecker I posted was a GM 3500.

An Eagle Cap 1165 has a COG at 61.5", or just over 5' behind the cab. That's right on the axle. Even if you shift that back another foot, we're talking 6000 lb-ft of bending moment.

If a wrecker can take 18000 lb-ft of bending, day in day out, for years before needing a frame repair, what made the Ram break after 1 trip?

That Ram / Eagle combo was together for 35,000 miles according to the owner when TFL spoke to him. Also he had one of those long extension tow bars on it for towing those aren’t cheap to setup. It’s unknown if or what he towed but at the time of the break he had an electric dirt bike hung on the back.

Plus he had some solid miles south of the boarder. Wreckers are typically short frames for strength and maneuverability they aren’t for long tow jobs so wheel base length and stability at speed when towing isn’t needed. I think the loads are different than a longer frame with that camper and likely higher speeds with some road surface abuse tossed in.

 

[RoyJ]

That Ram / Eagle combo was together for 35,000 miles according to the owner when TFL spoke to him. Also he had one of those long extension tow bars on it for towing those aren’t cheap to setup. It’s unknown if or what he towed but at the time of the break he had an electric dirt bike hung on the back.

Plus he had some solid miles south of the boarder. Wreckers are typically short frames for strength and maneuverability they aren’t for long tow jobs so wheel base length and stability at speed when towing isn’t needed. I think the loads are different than a longer frame with that camper and likely higher speeds with some road surface abuse tossed in.

I didn't realize the combo has been used for that long.

Based on the Raptor / ZR2 / Gladiator frame failures, I'd say big bumps, and many of them over course of 35,000 miles. The Raptors that broke their frames were carrying barely any weight.

On the other hand, a 30 foot Class C weighs a lot more than this Ram, much heavier rear overhang, similar frame strength, and go for 100s of thousands miles.