Does anyone know anything specific about the quality of steel used in the Long haul Trucker, And the quality of Al in the Trek 920?
I'm in the middle of an argument about steel vs. aluminum. And low grade vs. mid to high grade material.

just out of curiosity, why do you think anyone that posts in here would know about a mass produced frame? There are very few mass produced frame where they commit to use a particular type of steel, so it's possible it changes from frame to frame.

I'd also question what is meant by "high grade". Different alloys or material compositions have different characteristics for different needs. Add to that is the possibility that differing aspects of a frame might be served by differing materials. So a 4130 tubed frame might use a cast lug of a different steel and the braze ons or drop outs could be still another steel. With some AL frames there can be extruded tubes, die drawn tubes, machined bits and cast or forged parts. All needing their own spec.

When I've had these discussions with lay people (not that I'm a pro by any means) the unsaid assumptions/understandings are usually what's really being discussed, knowingly or not. Andy.

I should have gone back to my question about steel quality and re-read before I posted. I'm basically asking the same question about aluminum quality.
It never hurts to ask a question just maybe someone knows the answer.
Knowledge is power! Stupid lasts forever!!

As far as I can tell, the LHT is tig welded aircraft grade 4130 tubing. It is listed as having a double butted main triangle. Perhaps not as sexy as some of the new alloys, but it is a workhorse. Nothing mentions (on the Surly site) whether it is seamless tubing throughout, or not, but that would be a minor distinction.

Trek lists the frame as using Trek 100 alpha series aluminum. As far as I can tell, it may just be 6061, which is a very common weldable alloy.

One thing that Trek is doing is using hydroformed tubing. Some of it may be just for show and to imitate CF bikes. But, I think there are specific weaknesses in bike frames including the bottom bracket. Hydroforming allows shaping the tubes (and hopefully also tubing thicknesses) for optimum strength. At least in theory. Whereas the LHT has more of a traditional shape.

I've heard of frame failures with all materials, steel, aluminum, titanium, and carbon fiber. I couldn't say that any one material is particularly superior than another. But, perhaps it comes down to construction techniques.

The typical aluminum frame is much lighter than a typical high-ten steel frame. However, the differences are small when comparing to butted chromoly.

Perhaps one should look at one's intended riding. I use my Colnago Super for light to moderate on-road touring.

I'm wondering if the LHT and the 920 are speced for off-road riding. Build the frames for the worst conditions that they will encounter which makes sense from an engineering and warranty perspective. But, if your target is basic on-road riding, they are likely over-built.

You're going to get even less of a direct answer since the manufacturers often say basically nothing about the tubes they use. The LHT being listed as chromoly with double-butted main triangle tubes is vastly more specific than what you get with most of Trek's lineup.

If it means anything, the Trek 920 uses "100 series alpha aluminum", the same as on their entry-level 1-Series road bikes. It's sort of hard to infer anything from that, though.

Another thing that needs to be considered about metals, especially aluminum is the welding.

6061 is often welded with either 4043 or 5356 welding wire.

4043 isn't considered particularly heat treatable, and relies on dilution to achieve heat treating response.

4643 is supposed to be heat treatable.

I think there are supposed to be other heat treatable welding wire alloys.

Unfortunately, it may be difficult to find very fine process details on big factory made frames from China.

6061 is also supposed to be good for salt corrosion. Other alloys may be less salt resistant. Important for some riders, not for others.