> He ruled out magnesium, which is best per unit weight in compressive buckling but is brittle and difficult to extrude.
There's a fascinating, and very new, class of nano-laminate magnesium alloys called Long Period Stacking-Ordered (LPSO) alloys. These are very lean -- the standard version is 97% Mg + 1% Zn + 2% Y -- and they have outstanding mechanical properties. At an equal weight, they're much stronger and stiffer than 6061 aluminum, and the kicker is that this is generally true only if they're extruded. If they're not extruded, the laminate-like grain structure doesn't form properly.
Could make excellent bike frames.
Magnesium corrosion would still be a problem, though. I got some LPSO-Mg samples from Fuji Light Metals, in Japan, and they were quite badly degraded within weeks.
Cast magnesium is really weak/brittle compared to forgings and extrusions. Its use was not a great design decision on Kirk's part. I suppose they could have wrapped the casting in carbon fiber or something like that, to give it extra bending strength and spread out loads that might cause fractures, but then it would get expensive.
Can modern material science model this computationally, or does everything have to be observed experimentally? This kind of insane just-so recipe - are researchers just iterating on hundreds of thousands of different alloy compositions and production techniques or are there strong theoretical principles on which some of this can be derived?
Its been some time detached from the mat sci folks deeply involved in the space but its both. There is a bunch of theoretical underpinnings but ultimately a lot of throwing darts on the board as well.
Yeah. It depends a lot on the type of material, too. Conventional metal alloys -- like LPSO-Mg -- are the toughest to model. Too many variables. Ceramics and intermetallics are a lot easier to model in principle, but they can have surprising properties on an atomic level, and there's really no predictive method for that sort of thing. Modeling does get you pretty far with high-entropy alloys -- because to a substantial extent their properties hinge on how a bunch of different atoms might fit together randomly, and that's something that can be computationally predicted. A lot of the recent interest in HEAs is because they're relatively easy to model.
Interesting. I haven’t heard of them. Joining would still be a problem for a bike frame. Any idea on how well they work with other severe plastic deformation processes?
R.I.P. Sheldon Brown. I'm glad his pages still exist both as useful resource and as a time capsule of what the best of the old web looked like: useful, content rich, no ads, fast loading, stable urls.
It's interesting that trackies in the 70s were trying to reduce weight that much. I don't think it's perceived as especially advantageous these days. The high-ish end track bike I'm assembling now will be a little over 8 kg (almost 18 lb). We also race much bigger gears (typically 95-110 gear inches in mass start racing, bigger for sprinting) than mentioned in the article (72 gear inches). The position that is considered aerodynamic is also much different -- there is much less focus on getting that insanely low, and instead the focus is on being narrow and getting the forearms parallel with the ground.
It largely is the streetlight effect: we all have or can easily get tools to measure weight, we all have significant experience with weight, etc... Aerodynamics are much more difficult, especially in the 1970s where you can't just do some CFD simulations on your computer. There also weren't cheap solid state strain gauges to outfit wind tunnels or the bike drivetrain. Since only tiny aero gains are available without banned aerodynamic devices, there isn't much optimization you can do and need sensitive tools.
On a nice track, assuming a perfectly smooth surface and zero elevation change, I'm willing to accept the effect may not matter enough to care. But introduce even just a little bumpiness or some elevation change (perhaps in the track curves), and it might matter for someone pursuing the hour record.
You're not going up and down the track during an hour record. Just doing laps at the bottom (zero elevation change). Track surfaces aim to be very smooth in general.
Ok. Almost no impact. Worth keeping in mind we're talking about a system weight of like 180 lb vs at most 185 lb here (Merckx was ~163 lb), for a relative difference of up to 3%.
Two things jumped out at me: the simple/non-adjustable saddle support, and the absolutely slammed bars affixed just above the fork. Was that normal for track bars at the time?
Yeah, both are relatively insane choices by modern lights. You see some other track bikes of that era with fork-mounted handlebars (it's not unique) but I believe conventional stem + bars were more popular.
> Use larger diameter tubular components - Strength goes up as the cube of the diameter so unless there are geometric constraints, use larger diameter tubes with thinner walls to get a lighter structure with increased strength and stiffness.
This trend has continued -- it is very noticeable in road and mountain bikes.
But this trades off against impact resistance, aerodynamics, and the can-it-fit-between-your-legs-metric.
Klein bikes of that era had the best paint jobs I have ever seen. I was way too young to even know about these bikes back then, which is a shame, as they are pretty much at the very top of what constitutes bike porn for me.
The pinnacle of the modern tubular aluminum road bike frame was probably reached with the cannondale CAAD8 and CAAD9 frames, which could easily be built into UCI-illegal-weight bikes using expensive components and wheelsets.
I'm convinced titanium is a pretty optimal bike material. I hate aluminum frames, too stiff, some amount of flex makes a bike so much nicer. Hate carbon, too. Steel is nice.
I've have a lite ghisallo frame which I think was under 2lbs. The whole bike is under 15lbs and still manages to carry my 200lbs of weight.
Titanium frames have a devoted fan base. Personally, I tried to notice the difference back when I did road racing but didn't. Maybe I didn't want to: Ti ain't cheap.
Low quality steel is very cheap but also really heavy. You can get a whole crappy bike for a couple hundred bucks. Higher end steel isn't as cheap but is still relatively heavy (compared to aluminum or carbon). You can get this kind of bike in the $1000-2000 price range (e.g. Surly). Aluminum bikes tend to be inexpensive, but also not the lightest. These can also be priced at $1000-2000 (Specialized, Trek, Giant, ...). Carbon comes in a range of prices with various tradeoffs. You can get very budget carbon frames at like $1500 (Winspace) or whole bikes at like $3000 (Giant) (maybe $2000 in non-major brands, very discounted during current market conditions).
For titanium, I'm seeing Black Friday deals starting at like, $3200-3500 (Lynskey / Litespeed). But they're often sold at higher prices than carbon bikes. (For my money, I prefer carbon frames -- you get more flexibility in tube shapes and the end result can be lighter and stronger than titanium.)
Prices shot up during the pandemic and never really went back down. You're lucky to find a good carbon bike for under $4K these days where you used to be able to find them for $2K.
There's a fascinating, and very new, class of nano-laminate magnesium alloys called Long Period Stacking-Ordered (LPSO) alloys. These are very lean -- the standard version is 97% Mg + 1% Zn + 2% Y -- and they have outstanding mechanical properties. At an equal weight, they're much stronger and stiffer than 6061 aluminum, and the kicker is that this is generally true only if they're extruded. If they're not extruded, the laminate-like grain structure doesn't form properly.
Could make excellent bike frames.
Magnesium corrosion would still be a problem, though. I got some LPSO-Mg samples from Fuji Light Metals, in Japan, and they were quite badly degraded within weeks.
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