F-150 and Silverado 1500 all brag about using full boxed frames, yet their big brother counterparts such as the F-550 are still using c-channels?

Why is it that a brand new heavy duty 200k dollar commercial grade truck will probably still be using c-channels if a 15k dollar 1/2 ton pickup is using fully boxed cross members and frame rails and calling it superior? Are the bigger trucks just slower to change due to the industry sticking with what has been proven to work, or something?

 

I would say that weight on a commercial grade truck is significantly less of an issue than it is for consumer-grade trucks. That being said, if you compare the C-channels between the two grades, the commercial C-channels are probably much larger and thicker material, therefore full boxing probably wouldn't add much benefit.

Having the fully boxed frames adds rigidity when using thinner & lighter sidewalls. Kinda like a keystone on an archway.

 

I think boxed rails would be difficult to work with . Every time you bolt something to it and want to tighten down, you'd (potentially) crush the "box", whereas bolting to a C-channel, it's essentially a "plate", so you have bolt|plate|part, vs. bolt|plate|space|plate|part. Seeing how many parts (suspension, etc.) are bolted through the frame rails of big rig trucks, how could they possibly change to a design that would A) require more physical material (4 sides is ~33% more than 3) and would require extra re-inforcement at any attachment point??

I don't know for sure, but how many things are bolted THROUGH pick-up truck frames, vs. being bolted/attached to plates that are merely held onto the bottom of the frame rail?? Figure pick-ups carry FAR less weight than commercial trucks, so while they're using a "superior" frame rail, they still don't have to be as "beefed" up, in comparison?

edit: along the lines of what jpolz mentioned about material thickness, I'm sure what they've ADDED in boxing a C-channel, they've merely SUBTRACTED from overall thickness .

 

just a couple quick thoughts:

1. Open sections (channel) are less expensive to make than closed sections (tubes), especially when frame engineers want varying cross sections along the length as they do with most modern pickups. if it works why fix it? probably due to nvh and ride quality.. they want to build trucks that ride as nice as cars.

2. The closed sections are better torsionally than the c sections.. even in a full frame application.. however take a look at most heavy trucks and semi out there.. .they are mostly still open channel frame construction.

3. Corrosion would be more of a concern with the closed section frames. water could easily get trapped within, accelerating the corrosion process. open channel sections don't let water pool as much. (there are ways around this problem though)

4. The german truck manufacturer MANN, uses a welded fully closed rectangular tube frame system... so there are a few of them out there..

 

I think it is aimed more towards the ride quality and getting rid of vibrations

The big trucks will never go to a box frame

 

Actually, weight on a commercial truck is a big deal - each pound of truck subtracts a pound from cargo. It adds up over the life of the truck.

That being said, fabricating a closed-box frame rail in the length required for a commercial truck is not a trivial task, and the truck market in the US is not one that really encourages innovation at this time.

 

From what I have heard, it's because the large trucks need to have some degree of flex in their frames. A large truck's frame is very long and subject to very high loads, so you can imagine when the 4 corners are on different planes, a frame would have to be incredibly strong to stay straight and still not crack. By flexing, it allows the frame to absorb some of the load and not break.

 

BINGO.

 

Yup

 

I assemble Med Duty trucks, used to assemble HD trucks, and the "C" channels are 8" to 10" tall, 1/4" to 5/8" thick, and even use an extra inverted "L" plate on some models over top of the "C" channel for added strength.
And they are boxed with a counter "C" inside the rail, in the areas of engine/transmission mounting.
And they have several crossmembers also of a stamped and HD "C" variety for added strength.
And 90% of the frame rails are arrow straight, only lighter duty Low Profile models have bends in the rails.

This is such a big deal that we don't allow longer than "neccessary" bolts or rivets on these trucks...plus the cost savings.

 

Basically what this boils down to is I was saying how disappointing it was that the new Tundra still has some sections that are not fully boxed whereas GM, as of the 2007 model year, does. I was told that fully boxing wasn't necessarily superior and given the example of the big trucks that don't use it... I couldn't really say anything at all back since that's a good point, but all I heard over here was everyone automatically ******* on the new Tundra for using c-channels... especially one of our 'engineer' members in particular... so I'm really interested in his response in particular.

OK so if c-channels are used because the frames need to bend some, then why don't they use a fully boxed design and just use less material instead, to save on weight? I guess what I'm saying is it would seem even half ton trucks need to be able to bend some in the event of a wreck or hitting a big bump while carrying a load - so what made them decide to add rigidity by fully boxing the frame as opposed to one of many other methods for accomplishing increased rigidity, and why isn't the same decision made for the bigger trucks on the market?

 

Yeah me too... I'd love to know what that "engineer-guy" has to say about this... hmmm.

 

Too me it's not a deal breaker either way. Both would do all that I would need to do for a 1/2 Ton...

If I was using it for crazy pulling/work I'd get a 2500 or 3500HD anyways so it's a moot point for me.

 

Maybe because the box design loses rigidity when its shape is flexed?

 

That would be you, Proud. You're the guy who so giddily slammed the Tundra for using c-channels when the GMT-900 had just come out and for the first time eliminated them in the half ton model.

You are the one I'd love to hear explain why it's such a problem for the Tundra to use c-channels when most of the much bigger commercial grade trucks seem to be fine using them.