32

tl;dr heating chromoly to brass-brazing temperature doesn't really change it, at all; the steel was born hot and heating it back up does nothing to it other than oxidizing the surface if you don't protect it with flux. For special proprietary exotic steel tubes heating them up may or may hurt or it may help; there is no rule. There is much wrong, and not-...


18

I would not. Instead I'd strongly recommend you look at buying the bike you want rather than chopping up a working vintage bike. At best you'll come out with something worse than a replacement aluminium road bike, and perhaps slightly better or worse than the bike with which you started. A used 2000's bike would be a far better bike than some chopped-up ...


17

When you consider the overall outcome - the final bike, not just the frame, hand building in aluminum rarely makes sense. Modern aluminum factory frames are hydro formed into all sorts of engineered shapes that save weight and provide stiffness and compliance where needed. There is no way to hand build an aluminum frame even close to the characteristics of a ...


14

I'd go with full housing for both brake and gear cables and hold the cables on with cable clamps. There are many kinds of cable clamps to choose from. I prefer the type that have a screw clamp over the clip on type. The key will be finding clamps for your tubing diameter. If you need to have cable stops there are clamp on versions from a variety of vendors....


13

Interesting question and way of looking at it. Here's my take: those in the bike world who would seem most qualified to design scientifically optimal frames, which involves both mastery of all the advanced fabrication techniques and materials that are now available and the motivation to empirically figure out the handling and ride feel elements that can be ...


13

3D printing have many disadvantages: Materials cost and strength: although new materials has been made over the years to reduce the cost, it is still quite expensive for mass production. In our department, a good material would cost £10/g, and the cheapest is around £1/g (very porous and fragile). Labour cost: it takes time to CAD a small part, but it takes ...


11

There is a lot more to a bike frame than just weight. If there is one thing early aluminum frames taught us is that straight gauge aluminum rides harsh! Modern aluminum frames typically employ hydroforming to tailor the compliance and ride characteristics of the frame. This is why modern aluminum bikes ride a lot better than 90’s aluminum frames which were ...


11

Softride is one of the bigger names in this area. Their main bike design exchanged the top/seat tube and seat stays for a composite materials "beam" that cantilevered back to a saddle in the regular position. Originally for MTBs, they pivoted to Triathlon bikes in the mid 90s. The company stopped making frames in 2007 mostly because the design ...


10

The decimal sizes such as 25.4 and 28.6mm are not "unusual" sizes. They are actually the standard sizes. You can count on engineers to do the easy and cheap thing, so they use the standard sizes. "Standard metric size" tubing (that would presumably be sizes in a round number of millimeters like 25mm or 30mm) is not really a thing in the ...


9

Unless you are of extremely uncommon proportions, you won't find much riding advantage in a custom-made bike— there's plenty of room to tweak a mass-production bike for the a perfect fit through component swaps. Moreover, unless you buy from an experienced touring-bike specialist, it's entirely possible that a custom-designed bike might have little ...


8

You're almost certainly better off spending that money on going touring. I'd go so far as to say that until you have done enough touring to have a list of things that you want from your touring bike that you can't get from any production bike, don't bother thinking about it. Well, unless your other hobby is spending money, in which case I suggest buying one ...


7

The reason why flexible forks and stays are not used for suspension is geometry. With flexible forks blades or stays there is nothing that makes the left and right side of the fork flex together. Flexing one side more than other twists the wheel sideways, making it hit the fork. This is generally not wanted, and making the forks wider would just result in ...


6

I remember seeing courses about how to make a bike frame, but they were not about new designs, they used standard designs and the courses were about selection of tube, welding/brazing, finishing, etc. Perhaps you start by learning to braze, then building a "conventional" lugged steel frame, then develop that based on what you learn in the process. This ...


6

Too much "spring" is not always a good thing, especially when it allows the frame to flex in directions it is not supposed to. There is a video by Colin Furze where he makes several attempts to replace certain parts of a bike frame with steel coil springs of increasing stiffness. Even with the stiffest (and incredibly heavy) coils, the result was ...


6

Short answer: No. Bike manufacturers are certainly aware of the QC issues inherent in the carbon fiber manufacturing process and ways to both test for and mitigate them, and it is also true that for VIP's (i.e. flagship athletes) and during product development, a very small selection of VIP frames will receive additional scrutiny beyond the normal QC process ...


5

I suggest starting with a prototype made out of square tube and old bikes, especially if this is your first framebuilding project. Square tubing is a bit easier to work with (you spend less time mitring tubes) and the goal for the prototype is that it should be easy to build. Take shortcuts, in other words. Get something you can ride, then ride it. When ...


5

While you probably could cold set it, the Sturmey-Archer XRF-8 is available in a version with 120mm OLN dimension. (And you almost certainly can fit a modern bottom bracket. Worst case, have the existing threads removed and fit a threadless bracket. Bottom bracket size guide.)


5

Five years later, it turns out it was just a matter of time until 3D-printed (additive printing) titanium frames showed up: https://www.pinkbike.com/news/the-3d-printed-moorhuhn-is-now-available-in-full-titanium.html In the article above, Huhn Cycles announces their 3D-printed titanium bike, the Moorhuhn. There is also a 3D-printed steel version available ...


5

This is only engineering judgement, not technical analysis: the damage does not appear particularly serious or significant at that location. As Daniel advises above, keep an eye on it for cracks developing. If you are just a "normal" everyday type user it could be OK for quite a while. The Al frame will eventually crack and fail, not necessarily at this ...


4

Mattnz's answer is canonical and addresses aluminum, steel, and titanium frames. Until we can easily 3d print metal frames, custom frames are going to be tube based. Hydroforming metal for one-off bikes isn't worth it and you can't easily braze aluminum (you have to TIG weld it). But this leaves out another important material (as Chris H notes): carbon ...


4

It should be possible to repair the frame, the big question is whether you'll be able to find a replacement tube or will you have to make it yourself. Making the tube isn't hard, it's just messy. The repair will involve cutting out the damaged tube, working out what else (if anything) is damaged, and paying careful attention to the other tubes. Then once ...


4

The only real advantage to a compact geometry road bike is for the manufacturers. Since standover- which is the distance from the top tube to your crotch when you straddle the bike with your feet on the ground- is increased, one size of frame will fit a wider height range of people and therefore the manufacturer does not have to make as many different frame ...


4

You can't build any bike with minimal effort. Not even a toy one out of Lego. It would be faster and easier to get a minimum-wage job and save money to buy a commercially made bamboo bike. But a lot less interesting, and also less fun. Turning bamboo into something suitable for a bike frame is quite a lot of work, and if you haven't worked with structural ...


4

Also worth noting is that steel and aluminum have different electrochemical potentials (tendency to give up or accept electrons) which will result in galvanic corrosion over time, possibly to a catastrophic extent.


4

Specialized frames around 2010 used to have “Zertz” inserts “for a compliant, but super responsive” experience. Look at the seat stay, seat post and front fork: I think now they are instead using flexible seat posts and a real shock with 20mm travel built into the steerer tube (called “Future Shock“). Lauf makes forks with carbon leaf springs which ...


4

The hard part is that you don't just want a flexible frame and springy-ness. All bike frames do incorporate some level of flex. As soon as any structure is loaded, it deflects. In Engineering terms: if linear, it's called "Hooke's law", stating that the deflection is proportional to the applied force. In practice, that is clearly visible e.g. on a ...


4

What you are asking is engineering. Even if you can calculate the correct thickness for all "reasonable" impacts and forces thrown at a bicycle, you still need to take into account that the bicycle will be used, so the material will undergo hysteresis. A frame can stand a single impact providing a force of X, but it may fail after one hundred ...


4

I'm not really familiar with the bicycle production process, but in the case of motorhome manufacturing (Winnebago), two identical bare chassis come in the door on one end, and by the time they reach the exit door, one may be a $100,000 plain Jane, while the other chassis has been adorned such that the asking price has reached 175k or more. I suspect this ...


4

Ultimately, the cause of knee pain while riding is that we have knees. That, combined with a poor bike fit will give pain in knees. The human knee is a relatively vulnerable joint because it is at the end of two shafts and is abutted together while not being constrained as much as a hip or ankle. The elbow is similar. If you're having knee pain on any bike, ...


3

the step-through height must be no higher than the top of the pedal stroke, since the rider will need to have their foot that high to ride the bike. The exception, obviously, is bikes for people who can't lift that high but can accept forced motion that high. But those are generally built for rehabilitation rather than primarily for transport, like the one ...


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