Duragrouch

There's been a lot of experience in titanium welding, I have not heard of quality problems as all makers are high-end frames and bikes. I think it used to be needed to weld it in a vacuum, but for a long time now it has been successfully welded in an inert gas environment at the welding head.

The steel you mentioned I ran across a month ago, reading the history online of Reynolds 531 alloys and subsequent developments. Steel is amazing stuff, you can get extremely high strength, especially with maraging steels and such, but it does need to be drawn thin to have good weight, but with double butted tubes, that aids welding or brazing to lugs.

Duragrouch

I will also add to the Helix/Brompton/X11 debate: Since the patents on the Brompton frame design have long since expired, not only are there clones (aka "Brompnot"), but more importantly, the same frame design adapted to 20"/406 wheels, perhaps even 451 if you look hard enough. Usually these are welded instead of brazed as with Brompton, as 4130 steel welds just dandy. So if you like the Brompton-style frame, and want all-derailleur gearing and a bit more stable and comfortable ride with a wide range of tire selection available, a 20"/406 Brompnot may be your ticket; On 20"/406 you can easily get 400% gear range with either 1X wide cassette or 2X normal cassette, and with both you can have touring-capable gearing at 566% range. Tires you can get up to 2.4" wide I think, which is pretty cushy.

Jipe

The specific Brompton frame concept with the rear wheel folding right under the main frame tube has the drawback that any overall wheel diameter increase also increases the wheelbase, the folded length and folded height and the biggest advantage of the Brompton = its very small folded size is lost.

Kinetics has a lot of experience with Brompton upgrades, you can have a look at its 18" and 20" Brompton, you will immediately see the consequences of the wheel diameter increase.

For the derailleur Brompton; besides the narrow, not standard rear OLD, there is the still unsolved problem of the chain tensionning when the rear triangle is folded (the only clean solution is the LTwoo Fold B specific derailleur, when you see a picture of it, it looks nice but when you have it in your hands, you see that its really low quality and its really heavy).

For the welding of titanium, indeed it should be done in inert gas environment, it seems easy to do but its not, the tubes must be very well prepared, there should not be any remaining oxygen in the tubes and there are many cracked titanium frames also from well known manufactures. Usually, the frame last several years before it eventually crack, so owners do complain since the warranty is over since a long time, most owners do not understand that cracking is a consequence of a bad manufacturing.

Duragrouch

The welds I've seen on all titanium bikes, is often very minimal bead size; That may be a factor in durability. This past year I saw at the LBS, a Masi touring bike, steel frame, and I'll tell ya, the weld beads were incredibly neat and lovely, but *tiny*, looked almost like they were laser-welded together, if not for the actual weld bead additive materal, but it was small. I wondered about long-term durability. The lovely quality welds on my Dahon steel frame are no more than 1/3 of the width of weld beads on their aluminum bikes, but even that narrow bead is at least 2X the bead width on that Masi. Very elegant, but I wonder about durability.

Schwinnsta

Where are these 406 Brompton style bikes then? Perhaps, at this wheel size, the design does not hold up as well. I did see this on AliExpress and admit I am tempted, but the bike appears to be made of heavium, though that could be in the components. Good price.

Duragrouch

Others have posted about them on threads. I hadn't searched for them. That one you link to is not bad looking! Component set not too bad. Says rigid frame, no rear "damping", but I see what looks like a rubber spring between the rear triangle and seat tube.

Heavium, I like that, that's funny. 15 kg, yeah that is on the heavy side, 5 lbs above a 20" steel Dahon; my guess is made from simple "Hi-Ten" steel and not 4130 chrome-moly.

Schwinnsta

But it says CroMo. Usually they just say steel if it is Hi-Ten. Fork says steel. Net weight is given as 13Kg.

john m flores 

I think that part of the challenge in buying your first bike is that you don't know what you don't know and you don't know how your relationship to cycling will change and evolve over the years. You may find out that you enjoy quieter gravel roads. You may grow to love long trips.

The Tern looks like a great bike but it's really focused on doing one thing well - zipping through a well-paved city very quickly. But if you want to take Metro North up the Hudson River Valley to ride some gravel, the Tern won't be the right bike. Or if you want to ride part of the Empire State Trail, the Tern won't be the right bike.

I'd suggest more of an all-rounder for your first adult bike so that you can try different things and find out what you like. Of the three bikes you're considering, the Helix seems the most all-rounder. You might also look at a Bike Friday New World Tourist. It's more of a travel bike than a multi-modal transit bike, but it's a nice-riding folder.

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2_i 

I have 50/43/20 in the front on Brompton + at least 11/12/14/16 on BWR in the rear, and the Brompton Advance type tensioner picks up the slack for the folded bike no matter what gears I leave the bike in. It is an astoundingly effective device, never meant to be pushed this far, and the same is true for the non-Advance tensioner. In my memory, the Ltwoo derailleur is way ineffective in comparison, capable of working only with a single front gear. In Birdy, you have to leave the bike in specific gear for folding, and then take the seatpost out or something, in my memory - just ridiculous. Once upon a time, I thought plastic in derailleurs was inferior to metal - now I know that depending on the particular element, it may work better.

Jipe

I mean no crappy BWR hub too, a real 11s derailleur with a real cassette. And no triple crankset, another remnant of the past same as the 4s cogset and derailleur.

On the Birdy, the only constrain is to put the chain on the smallest cog but this is not due to the chain tensionner, its due to the shape of the rear swing arm.

The rear swing arm locking works exactly like on the Brompton: its the seatpost pushed down that locks the rear swing arm folded.

With your setup, I doubt that the chain remain tensionned with the chain on the 20t chainring+11t cog?

Jipe

The problem with oxygen contaminated titanium welding most of the time happen inside the tubes, some oxygen remaining inside the tube while welding.

When this happen, you cannot see anything from the outer side of the tubes, you only see the problem when the frame is broken, then you see the typical color of oxygen contaminated titanium welding.

2_i 

The 'crappy' BWR and the rest give me the range from 1.03 to 9.16m of development, of which the extreme ends I use daily when I ride on E African Rift. If you always ride in one or other flatland, you may claim that a single speed is sufficient. I take the folding bike to various places and want it to be maximally flexible. BWR is a wonderful piece of engineering that solves the small-wheel high-gear problem, and once that problem is solved, you use the planetary system in reverse and get low gears, too. It is brilliant. Of course, my chain is tensioned on the 20t+11t combination, whether in riding or folded. Oh yes, and the wheels are round as the remnant of the past

Duragrouch

Typical color... white titanium dioxide?

Duragrouch

Typical color... white titanium dioxide?

Jipe

No a blueish color of the welding.

The problem with a triple chainring+BWR+4 cogs is the low usability consequence of the 3 commands and the slow gear change due to the BWR and poor 4s Brompton derailleur.

I do not see any use of more than 9m on a Brompton and below 1.5m, the rear wheel, even with good tires, has no grip anymore. Even with 1.5m on a wet surface or worse cobbles, its difficult to start after a stop in a steep hill.

My Rohloff solution on the Brompton with 1.54m to 8.11m provide low enough+high enough gear inch with one single command, ideal gear spacing and a high efficiency for a lower weight than your complex solution with 3 commands.
But a real 11s derailleur with a 9-32 or 9-34t cassette like on the Birdy would be enough for most situation with a much lower weight.

2_i 

I do not quite understand what you are saying. However, if it is about convenience, the front derailleur shifter on my Brompton works like a button that changes the range of the gears, from high through middle to low, according to the riding circumstances. You touch it when the circumstances change. The two other shifters are analogous to two on any touring bike. My controls are positioned similarly on full-size and folding bikes to keep the instincts the same.

The 9.16m on Brompton is for fun. When going shopping in Africa, I have a long descent on a wide, good-quality road and can do 80 km/h there. As to the low-gear end, I am baffled by your categorical statements. On my full-size bike, the range is a tad smaller, as my immediate surroundings are more limited, but I normally use 1.29m there to get out of ice ditches. When I ride out of my workplace in Africa to the main street, I first ride on 1.17m or 1.37m to get to the middle of the slope, then switch to 1.03m. The latter is the only gear I have to get me all the way out to the main street. The grip is not a problem yet; switching the gears is when the chain is maximally tense. You must strategize, switch ahead, and exploit ground undulation and turns. Starting from rest is a problem, too; you may need to start without going straight up or walking up to a piece with a milder slope - it is all part of riding fun.

It is common for complex optimization problems in many dimensions to have multiple extrema. When varying secondary considerations play a role, no absolute favored extremum is common. It defies me what a "real" derailleur is.

davidhunternyc

Great idea. Yes, I found some place in Asia that sell "Brompnots." I can't tell if they're any good or not. Some people say the quality isn't there. I don't care about the label so if the quality is there, this could be an option.

davidhunternyc

Great advice. Will do some more research. I'm not a gravel person though. I just want a bike for urban riding. I'm stupid too. Never heard of the Empire State Trail. Doh!

Duragrouch

(I can't recall if mentioned previously): Brompton and clones are on 16"/349 tires, which have limitations, as explained below. If you want the same frame folding *style* but in the larger 20"/406 wheels, some have said in other threads that frames are available for that, but you may have to build this up custom yourself or via a bike shop.

Bromptons and clones, are typically 2 cogs with 3-speed internal gear hubs (IGH) for 6 speeds, needing the IGH for an overdrive to get a reasonably high enough top gear with those small 16"/349 tires; You might be able to get there with just external derailleur gearing, but you'd need a big chainring and small cog like a 9 tooth high, or a Schlumpf drive in the bottom bracket, so essentially a different kind of IGH in a different location. Also, tire selection in 349 is limited, mostly 1-3/8" I think.

With 20"/406 wheels, they are large enough to not need an IGH for a decent top gear, with standard 11 tooth high cog and 50 chainring, you have 85 gear inches. To get lower gear than typical folders that are above 30 gear inches, you can install a double chainring (50/34), that gets you 21 gear inches with a 30 or 32 cog if I recall, or just a 1X cassette with 44 low cog. You can go lower to 15 gear inches with wide 1X cassette AND double chainrings. That's a great range with only derailleur gearing, if you prefer that over an internal hub gear. Plus, 20"/406 gives you a very wide selection of tires, from I think 35mm to well over 50mm (2.0").

My bike runs 20"/406, but is a bifold frame, not nearly as compact as a Brompton style fold, a pain to carry folded, and will be a struggle to fly with it, needing a good deal of disassembly and packing to do so. A Brompton-style fold would be a breeze, carries well or rolls, and could fly with no disassembly, but compact enough I think to fit in checked bag limit of 62" max girth. I KNOW a standard Brompton/clone on 349s would fit, not certain about same style with 20", but I think a real good chance.

Anyway, I hope that clears things up.

Additional: Cheap Brompton clones (349 wheels, IGH) are typically $300 shipping to USA. If I travel in Asia, if cheap enough for credit card touring, my plan would be to buy a clone there, tour, and then fly back with it, no shipping charge.

john m flores 

You're not stupid, just a bicycle newbie. Love your enthusiasm; hope that whatever bike you choose takes you places.

mallomar

Did you get that test ride? If not, you're welcome to try mine if you can wait a little bit as I'm out of town until later in the month. Feel free to send me a DM if you'd like.

davidhunternyc

No, I have not had a chance to ride it yet. I've not heard back. Yes, I would love to try your Helix! I'm patient. I've waited 4 years. I can wait a few more weeks. Thank you so much for offering!

Hrodwolf

I came with the same plan when I checked shipping a 20" clone to Europe.
Thank you for your insights into the technical aspect.