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

[rruff]

Since that bending moment occurs at the double framed and tall section, it's unlikely to actually bend.

I don't know about other makes, but on the Tundra the wimpy part of the frame starts at the forward spring mount and extends aft. The rear of the frame is the same for all bed lengths; it's the length of the heavy rails under the cab that changes. Extended cab or standard cab 8' models both have a forward bed mount that ties into the beefy part of the frame, but the 6.5' and 5.5' models do not. The 6.5' bed uses the exact same 6 bedmounts as the 5.5'... the forward ones are just a foot further from the front of the bed, while the 5.5' ones are very close.

 

[neliconcept]

View attachment 759525
This was posted recently on the “Overlandy Meme Thread“. Having seen a video of his in the past and thinking it was a well-built Tundra, I found these two videos about how this happened that are quite detailed and pretty interesting as to the cause and results of the event (along with being typical Youtuby clickbait epic journey stuff).

The first video (chapter four, part two) shows the actual incident that bent the frame starting shortly after the 17 minute mark. The second video (chapter five) recaps the issue, but then goes on to show him limping this screwed up Tundra up over Lippincott Pass (during the night and with a fast leaking, radiator!) into death Valley where he gets picked up.

The owner appears to have built this rig to be a combination overland vehicle, and a desert racer. Early in the chapter 4 video, he speaks about the suspension allowing him to bomb over the road, and mentioned he’s going 65 mph in one stretch. You’ll see the frame bending incident was him miss-gauging a dip in the road because he was going so fast. He also mentions that he can’t believe how well the truck handles the camper despite the camper’s 2200lb weight! I suspect this guy is/was more than double his trucks payload, not to mention it’s a crew cab and the camper sits farther back.

He sure made a lot of questionable decisions, and he does admit to everything that happened being fully his fault, but he doesn’t address the role speed and weight played in the problems he had. I pretty much think he’s an idiot, but I have some grudging admiration for how he got himself out of the fix he got into, and the toughness of the poor Tundra.

well forgive my language but this guy is an idiot. Putting what like 3-4k pounds on the back with the FWC? Maybe less but not a lot less. I plan to do a overland/desert race truck combo but I'm going with no more than 500 pounds in my bed in a 18 Ford Raptor that I plan to mid travel. No way would I put a flat bed on it with a camper shell.. If I did camper the rear it would be a GFC and that's it... Not only that, this guy obviously has stock lower control arms and probably stock rear suspension locations without running bypass shocks on a cage..

People like this guy add shocks with external resi and think they have a truck that can take whoops at 60 plus

 

[Ozarker]

Ahh, that's what I love about this site, so many automotive engineers with engineering degrees, talking out their azz , speaking to issues they haven't been exposed to and giving advice or opinion without a clue of actual use of a vehicle.

Typical forum BS.

Everyone knows the aluminum bodied F-150 with a 5.0 V8 can tow 3 Bradley vehicles while pulling 2 M-1 tanks through 6' of Louisianna mud in a bayou without having to shift from second to third with its 10 speed auto transmission.

Get Real, where have you people been?

 

[RoyJ]

Ahh, that's what I love about this site, so many automotive engineers with engineering degrees, talking out their azz , speaking to issues they haven't been exposed to and giving advice or opinion without a clue of actual use of a vehicle.

Typical forum BS.

Everyone knows the aluminum bodied F-150 with a 5.0 V8 can tow 3 Bradley vehicles while pulling 2 M-1 tanks through 6' of Louisianna mud in a bayou without having to shift from second to third with its 10 speed auto transmission.

Get Real, where have you people been?

Engineering is so over-rated... BRO science all the way!

 

[RoyJ]

I don't know about other makes, but on the Tundra the wimpy part of the frame starts at the forward spring mount and extends aft. The rear of the frame is the same for all bed lengths; it's the length of the heavy rails under the cab that changes. Extended cab or standard cab 8' models both have a forward bed mount that ties into the beefy part of the frame, but the 6.5' and 5.5' models do not. The 6.5' bed uses the exact same 6 bedmounts as the 5.5'... the forward ones are just a foot further from the front of the bed, while the 5.5' ones are very close.

Interesting. On Ram 1/2 tons, 5'7 beds have forward bed mounts rear of the control arm bracket, and 6'4 beds slightly ahead of the bracket.

In my future crew cab 5'7 bed build, the rear seat is coming out, and heavy stuff will be stored in its place (batteries, water, etc.). The bed will have nothing heavier than an aluminum canopy as the shelter, and 2 - 300 lbs of gear.

 

[NoDak]

Keep seeing loads compared to that encountered by tow trucks but tow trucks are almost always built on chassis cab trucks. Totally different frame construction from the cab rearward.

Edit: Doing a bit of research also seeing that chassis cab trucks fully boxed section from the front to back of the cab is about 1/4 inch thicker that a conventional truck with a box.

 

[rruff]

1/4" thicker? 6mm? That's huge! Where did you see that?

 

[NoDak]

1/4" thicker? 6mm? That's huge! Where did you see that?

I mistyped that. 1/4" total thickness for the boxed section of a chassis cab 1 ton. Specifically a Ford F350 chassis cab.

 

[rruff]

Did you by any chance see specs for the pickup version or the rest of the frame?

 

[NoDak]

Did you by any chance see specs for the pickup version or the rest of the frame?

I haven't seen it yet for the Ford. I've only seen comments on other forums regarding the Ram 3500 chassis cab frames at 3-4mm for the front section.

I got the Ford info here.

 

[pappawheely]

I can't imagine why they break where they do.

 

[rruff]

I can't imagine why they break where they do.

Actually if there is a relationship between torsional stiffness and vertical strength, it would tend in the opposite direction. All the >1 ton frames still use C-channel for the bed/body rails and are very torsionally flexible, yet they don't break vertically.

 

[RoyJ]

I mistyped that. 1/4" total thickness for the boxed section of a chassis cab 1 ton. Specifically a Ford F350 chassis cab.

http://d3is8fue1tbsks.cloudfront.net/PDF/Ford/Ford f350 450 500 cab chassis spec.pdf

Page 19, F350 chassis, 36 ksi frame, 8.7 sec modulus. 26,100 lb-ft bending strenght, believe it or not, lower than a modern Ram pickup. Thickness by itself can be deceiving.

I feel we're all looking too deep into tow trucks, I brought it up only to show:

1) the bending stress towing any car with a wheel lift is higher than overloaded Eagle Cap camper (did the math)

2) the Ram failed in under 30k miles, many tow trucks of similar frame strength (where everyone seem to focus on) go on for 200k+ miles

Therefore, something else beyond just overload caused the Ram failure - bottoming out, frame defect. If the guy used a 4000 lbs camper, drove the exact same way, no one can guarantee the frame will not bend.

 

[pappawheely]

Actually if there is a relationship between torsional stiffness and vertical strength, it would tend in the opposite direction. All the >1 ton frames still use C-channel for the bed/body rails and are very torsionally flexible, yet they don't break vertically.

That's my one ton truck. Just pointing out how much frame movement takes place between the bed and the cab.

 

[rruff]

That's my one ton truck. Just pointing out how much frame movement takes place between the bed and the cab.

Right, but it's C-channel and Ram in this thread is fully boxed and much stiffer in torsion.