I think the GBW is the stoutest rough stuff loaded camping bike RBW makes, and no double top tubes there. So clearly RBW doesn't think twin top tubes or diagatubes or rainbow tubes are the only way to make a large frame with the strength / stiffness they want in a touring bike. For some of the frames they choose to go the extra tube route to get the strength / stiffness they want for that model in that size (I presume). To my eye the MIT Atlantis is a complete redesign, longer chain stays, more tt slope, who knows what all else is altered from the original. I wouldn't be surprised if the existence of the extra tube influenced the choice of tubing specs. It may be overly simplistic to assume that all things are equal except for the addition of a whole nother tube. It seems possible that the presence (or absence) of an extra tube on a particular model and size of RBW frame tells less about its mechanical properties than some of us tend to think.
If I were in the market for a frame for the uses RBW recommends the Atlantis for, and was tall enough to ride one with a rainbow tube, I wouldn't be second guessing Grant about that tube being an appropriate design choice unless I disliked the way it looks. YMMV of course. On Wednesday, August 5, 2020 at 3:29:15 PM UTC-7, Steve Palincsar wrote: > > And yet, the original Atlantis was also meant for loaded touring, > performed splendidly in that role, and lacked the second top tube in all > sizes. > > > On 8/4/20 11:01 AM, Vincent Tamer wrote: > > The whole point of the Atlantis is that it is meant for loaded touring. > The second tube goes on the bikes for taller riders who are presumably > heavier. That along with a heavy touring load makes the extra tube a good > idea. > > On Tuesday, August 4, 2020 at 6:58:58 AM UTC-7 Patrick Moore wrote: > >> You are right that a second top tube will do something structurally; >> there's no avoiding that, and I overstated my own case. But my point is >> that for anything but a very large frame, or for a frame to be ridden by >> someone exceptionally heavy, there's no **practical** purposes served by >> the added tube. >> >> Still, that Atlantis frame does look very pretty; far nicer IMO than the >> other models with 2 top tubes; they got the mix of straight and curved just >> right. >> >> On Tue, Aug 4, 2020 at 12:07 AM S <sbl...@gmail.com> wrote: >> >>> As is my habit, I overstated my case. What I said is technically true, >>> because of physics, but I can believe the real world effect might be >>> negligible. >>> >>> In the back of my mind was the side discussion on here or iBob about the >>> supposed deadness of the Surly Cross Check frame. Some forum members -- me >>> included -- insisted the frame was a dog, no question, while others >>> disagreed. As it turned out, those in the former camp had the 56 and those >>> in the latter camp larger sizes. The theory was floated that maybe the >>> frame "opens up," that is, flexes more, in a good way, in the larger sizes >>> -- and with generally heavier riders -- and that accounted for the >>> difference. To me, this seems plausible. And if it's plausible that a frame >>> could improve in this way, then it also seems plausible that, conversely, >>> some frames could open up *too much* and become too flexy, in larger sizes, >>> thus necessitating some modification to maintain the same relative >>> stiffness as in the smaller sizes. >>> >>> Also in the back of my mind was the experience of my larger cycling >>> friends who seem to break more frames than I ever have. But then, that's >>> anecdotal. >>> >>> I don't know if Grant ran any numbers or did any testing before deciding >>> to add the second tube to some bikes. Could just be for looks, or could be >>> a belt and suspenders kind of thing. Or a mix. But I wouldn't say it's >>> totally off base from an engineering point of view. >>> >>> Anyway, you've ridden more 60 (and maybe 60 plus?) size frames than I >>> have, and if you say you don't feel a difference, then I can't argue. >>> >>> On Monday, August 3, 2020 at 8:27:15 PM UTC-7 Patrick Moore wrote: >>> >>>> Not true at all, unless -- perhaps -- you are well over 200 lb and >>>> carry heavy loads. I owned and rode a 60 c-c frame extensively -- my best >>>> level top tube size is 60 c-c -- and there was no more flex notiher 6- X >>>> 56 >>>> c-cceable than with an 18" mountain bike frame. And this frame was made >>>> from standard gauge, and not OS, tubes. >>>> >>>> I currently have another 60 X 56 c-c frame being refurbished; this is >>>> also standard gauge, and it is *very* light: 5.9 lb for frame + fork + >>>> steel Campy headset; I *do not* expect to need a second top tube. I'm >>>> 175. >>>> >>>> And my best load carrier of all time, that happily and securely carried >>>> 40+ in back (on an 11 oz rack!) was made from standard gauge, lightweight >>>> 531 and was noticeably lighter than my 2003, 58 c-c Riv frame that weighed >>>> 7 lb for frame + fork and Ultegra headset. This frame was a 58 c-c, IIRC. >>>> >>>> For anyone under say 250 lb who does not carry camping loads, a second >>>> top tube is ornamental, not structural. Amen. >>>> >>>> Back when I lived in India and Pakistan and Kenya, you'd often see >>>> heavy duty models of the stereotypical rod brake roadster wtih a second >>>> top >>>> tube (and with heavy aftermarket fork braces), but these were bikes >>>> cheaply >>>> made from cheap, weak tubing that carried 100 lb loads of firewood or 200 >>>> lb loads of charcoal in gunny sacks, or a family of 4; even so, most >>>> Indian >>>> and Pakistani made r b roadsters have single top tubes. >>>> >>>> Upshot: they look cool, but their benefit is purely aesthetic. >>>> >>>> On Mon, Aug 3, 2020 at 8:19 PM S <sbl...@gmail.com> wrote: >>>> >>>>> Yes, the extra tube strengthens the frame. Otherwise you would be left >>>>> with a wobblier triangle and have to use thicker tubes and there goes at >>>>> least some of your weight savings. I think it's a good solution and looks >>>>> cool, so a double win. >>>>> >>>>> On Monday, August 3, 2020 at 11:42:08 AM UTC-7 Jason Fuller wrote: >>>>> >>>>>> I can imagine it's useful once you get into the 60cm range, since the >>>>>> average rider weight is going up while the structural triangulation of >>>>>> the >>>>>> frame is going down. But I can't deny that I love the totally >>>>>> unnecessary >>>>>> extra tube on the Hunq so who am I to judge. >>>>>> >>>>>> The "unnecessary tube" I want, and would put on a Riv custom if I >>>>>> ever got one, would be the lift handle from the Rosco's. I keep hoping >>>>>> for >>>>>> it on new models. >>>>>> >>>>>> On Monday, 3 August 2020 at 09:00:02 UTC-7 Patrick Moore wrote: >>>>>> >>>>>>> I don't want a second top tube on any bike I own because it would >>>>>>> serve no real purpose and add needless weight (and also, perhaps, >>>>>>> rigidity >>>>>>> where I don't want it), but I do have to say that the curved second >>>>>>> tube on >>>>>>> those Atlantises looks wonderful *as sculpture.* In fact, merely >>>>>>> aesthetically, I think that edition of the Atlantis is one of the >>>>>>> prettiest >>>>>>> bikes, if not the prettiest bike that Rivendell has made. >>>>>>> >>>>>>> In other, and very unrelated news -- but I opened the window at the >>>>>>> same time as I opened the Blug window -- fenders are going >>>>>>> road-mainstream: >>>>>>> >>>>>>> https://www.bikeradar.com/features/bikes-with-fender-mounts/ >>>>>>> >>>>>>> Patrick Moore, who would indeed install fenders on his Atlantis if >>>>>>> he had an Atlantis. >>>>>>> >>>>>>> -- >>>>>>> >>>>>>> >>>>>>> ----------------------------------------------------------------------- >>>>>>> Patrick Moore >>>>>>> Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum >>>>>>> >>>>>>> -- >>>>> You received this message because you are subscribed to the Google >>>>> Groups "RBW Owners Bunch" group. >>>>> To unsubscribe from this group and stop receiving emails from it, send >>>>> an email to rbw-owners-bun...@googlegroups.com. >>>>> To view this discussion on the web visit >>>>> https://groups.google.com/d/msgid/rbw-owners-bunch/eca5c5da-6b50-4e9d-8f49-b67f5cf68363n%40googlegroups.com >>>>> >>>>> <https://groups.google.com/d/msgid/rbw-owners-bunch/eca5c5da-6b50-4e9d-8f49-b67f5cf68363n%40googlegroups.com?utm_medium=email&utm_source=footer> >>>>> . >>>>> >>>> >>>> >>>> -- >>>> >>>> ----------------------------------------------------------------------- >>>> Patrick Moore >>>> Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum >>>> >>>> -- >>> You received this message because you are subscribed to the Google >>> Groups "RBW Owners Bunch" group. >>> To unsubscribe from this group and stop receiving emails from it, send >>> an email to rbw-owners-bun...@googlegroups.com. >>> >> To view this discussion on the web visit >>> https://groups.google.com/d/msgid/rbw-owners-bunch/37f7aaa9-adbd-4329-bf5c-eab5cba24d9en%40googlegroups.com >>> >>> <https://groups.google.com/d/msgid/rbw-owners-bunch/37f7aaa9-adbd-4329-bf5c-eab5cba24d9en%40googlegroups.com?utm_medium=email&utm_source=footer> >>> . >>> >> >> >> -- >> > -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. 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