On a Columbus Tre Tubi frame, what are the stays and fork made of? Are they cheaper, seamed tubes?

It totally depends on the brand, model and production year of the frame.

As indicated, all but the main tubes are of some presumably lesser-quality tubing, but usually this only implies heavier tubing, not weaker.

If anything, the non-branded tubes are likely stiffer and more dent-resistant.

Pvc

LOL, methinks one day soon we might have to closely inspect all of the new Tre-Tubi carbon frames.

When I first acquired the Bianchi and inquired about TreTubi frames, I was told that Bianchi often used CrMo forks and stays, but that these were seamed and not Columbus-branded.

My same-period Peugeot PKN-10 was of comparable quality, with the three main tubes of butted Reynolds 531. The fork blades had obvious seams running up their trailing edges. If the Bianchi forks are also seamed, the finish work hides the fact well.

Mixed tubesets were very popular on midgrade frames of the 1960s through at least the early 1980s.

I would agree with dddd that it 'just depends'. I know from the catalogs that before Bianchi came out with Special and Formula frames they used Columbus main tubes, no grade given, and Falck stays, and some are listed as Tre Tubi w/ Alle stays.

With Trek- Until 1986- the "600" series bikes had a 531 main triangle and depending on year/model- the fork and stays would be made of 501, Mangalloy, Ishiwata... in 86, the lower mid-range bikes got the 531 main triangle with Tange CrMo forks and stays and the mid-mid range bikes got the 531/501 mix.

I'm not exactly sure how it played out for Tenax-

In any case- I think the concept more points to a more stronger bike at the expense of weight than out of price consideration.

I thought the whole point of using higher grade tubing is that you get could the same strength at a lower weight? I also suspect that decision to use 3 main tubes 531 and/or columbus tretubi was a good marketing tool (since the main triangle was made of a high grade steel) and a way of making the bike less expensive.

Not knocking tretubi or R531 main triangle bikes as many great riding bikes were made this way. One of my favorite bikes was a Pug PKN 10 which had a Reynolds 531 main triangle and I believe high tensile steel fork and rear triangle.

I really don't know, so I'm more "supposing" more than anything...

My understanding is your premium tubesets- 531c and Columbus SL were strong- but lacked the strength from mass- So in the case of specialized touring and 'heavy duty' sets, that extra strength and mass of the 501 or 4130 was preferred over the springyness of the lighter tubes. Think of the big knock on the 720- that it's too flexy. You're not getting that from the 620 or something like the Passage with that long wheelbase but with CrMo in the stays.

I do think towards the mid 80s there was as much of a price consideration- in getting mid-grade frames with a 531 sticker on them. I don't know if that helped as far as moving more product or made 531 less exclusive...

bassogap-

Italian TreTubi frames frequently used Falck tubing for forks and stays with Columbus in the main triangle. As the price point declined, hi-tensile was used. French frames with 3 main tubes 531 often added forks and stays of Durifort/888 or of hi-tensile. Peugeot used 531 main tubes and their own Peugeot-made hi-tensile. The Brits pretty much did 531 mains and high tensile. As bikemig says, very much a marketing technique but some lovely bikes were made this way.