Trend favors fewer cylinders

[darcane]

Originally Posted by redpoint5

I'm curious why Ford choose to use aluminum for the body and steel for the frame instead of the other way around? I would think the bulk of the weight is in the frame. Body damage is also more likely than frame damage, so making the body out of steel would reduce repair cost.

I have a feeling my insurance rates are about to go up as the cost to repair vehicles skyrockets.

Truck bodies are split in the middle (between bed and cab) so the body does not add to the rigidity of the frame. As you load up the truck and/or go over large bumps, the frame will flex in the middle. With a steel chassis, this flexing won't damage it because steel has a very high fatigue life. Aluminum will eventually fatigue and crack unless a lot of extra material is added. This would probably exceed the weight of the steel frame for the same load.

[Focus-Ak]

Originally Posted by darcane

... With a steel chassis, this flexing won't damage it because steel has a very high fatigue life. Aluminum will eventually fatigue and crack unless a lot of extra material is added.

It's the other way around. Aluminum has an infinite fatigue life, once beyond an initial period of load under vibration. Steel is always subject to a possible fatigue failure, given enough vibration cycles.

[elhigh]

Originally Posted by Focus-Ak

It's the other way around. Aluminum has an infinite fatigue life, once beyond an initial period of load under vibration. Steel is always subject to a possible fatigue failure, given enough vibration cycles.

Sorry, you have it backwards:


That's why, even though they're heavy and add weight where you don't want it, springs are still made of steel.

[UFO]

Originally Posted by elhigh

That's why, even though they're heavy and add weight where you don't want it, springs are still made of steel.

That's also why airplane airframes are CONSTANTLY inspected.

[redpoint5]

I also wonder why more trucks haven't adopted the unibody construction. It seems silly to separate the cab and body. After all, cars don't have separate passenger and trunk sections. What's good for the goose is good for the gander, right?

As an aside, I hauled 2 yards of river rock in my "3/4 ton" truck last week. I knew it was a big load because the front end wanted to wander more than usual. The trailer with 3 yards of bark dust might have had something to do with that also. From what I'm reading, I had somewhere around 6,000 pounds loaded on the axles of my truck in addition to the truck's 7,000 pound weight... and I thought maybe I could do 3 yards of rock

[Frank Lee]

"Unibody" trucks have been done; Ford had one in the '60s and of course there are littler ones like Ridgeline, VW Caddy, utes, and so on.

The '60s Ford was still body-on-frame but I've read there were complaints that the doors were hard to open/shut or wouldn't open/shut if the truck were heavily loaded, especially a few years on with rust. Oops. Helps to isolate the cab from those stresses. Yes, I know this only applies to the 1% of pickups that are called upon to haul more than groceries.

But I think the main thing is that a "uni-cab" reduces the versatility of the layout as seen when boxes are removed and replaced with dump boxes, flatbeds, hi-cubes, etc.

P.S. The truck should still have ALL it's structural integrity without the box and without adding braces and such when sans box.

P.P.S. And the thing shouldn't fold in half 10 years down the road when you put a load on it and the tin is compromised by RUST (since the mfgs design their junk to rust out on purpose at about 10 years in the Rust Belt).

[P-hack]

Looking at the back window/door jamb, it doesn't look like a truck body would make a terribly rigid unibody anyway. A car has an extended roof and pillars that distribute the load.

[elhigh]

I look at the various ways you can purchase a truck and find that the unitized construction, while thrifty and lightweight and perfectly okay for a car, would be a serious limitation for something as versatile as a truck chassis.

I'm thinking just of my old Toyota right now, but it applies across the entire range of pickups, even today.

The smallest U-haul used to be a Toyota cab and chassis, with a small box, about 8'. Remember those?

Going up a size, there were the many compact RVs based on compact pickups. There are larger models based on the larger American models too:
This is about as much as you can reasonably expect of a compact pickup chassis, except...

The Hilux was available as a 1-ton model, even with duallies and a flatbed (stakes optional)

I liked those and when I was shopping for a truck, I looked for one on the used market. No dice.

So while it might make sense in certain paradigms to consider a unitized chassis for trucks, in most paradigms it doesn't. There are too many sub-markets that use the truck as a starting point for their product. Granted they don't represent a large portion of the market but when did you last see any manufacturer willingly cede ANY sales to a competitor?

I can only think of two exceptions to this: the Honda Ridgeline and the Subaru Brat. The Brat was never considered a real truck, not even by Subaru. They were actually trying to horn in on compact truck sales with a truckified Loyale. And Honda will call their crossbred monstrosity a truck, but precious few people (Motor Trend and its dubious judgment notwithstanding) will look at that thing and call it a truck. It's a tall car with a lidless trunk.

[gone-ot]

Uni-bodies included the Chevy El Camino, Ford Ranchero, and Dodge Rampage, I believe.

[basjoos]

Also the VW Rabbit pickup.