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MIT Aluminum Bicycle Project 1974 (2016)

sheldonbrown.com

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Re: MIT Aluminum Bicycle Project 1974 (2016)

#101

Post by bluGill »

cenamus wrote: post #54
loeg wrote: post #5

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 consid…

Maybe that's just mostly due to the UCI regulations? No point to develop a fully fitted 5kg bike if it has to be 7kg anyways I suppose

If you have a 5kg bike you can put the extra 2kgwhere you want it. this can make a difference in a race.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#102

Post by jdietrich »

cenamus wrote: post #54
loeg wrote: post #5

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 consid…

Maybe that's just mostly due to the UCI regulations? No point to develop a fully fitted 5kg bike if it has to be 7kg anyways I suppose

Most competition bikes weigh significantly more than the 6.8kg limit, because weight just doesn't matter very much. A lot of state-of-the-art road and track bikes weigh around 8kg.

On the flat, weight only affects you during accelerations - at a steady speed, it has no significant impact on performance. Aerodynamic drag and rolling resistance are constantly sapping away power, so features that reduce these losses are nearly always worthwhile even if they increase weight. Even on a moderately hilly road stage, aero trumps weight by a considerable margin; on the track, weight is almost entirely irrelevant, particularly in longer events.

A lot of riders like the feel of a lightweight bike, a lot of them believe that light bikes are faster, but that's only true on exceptionally steep stages or hill climbs.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#104

Post by dahart »

xpe wrote: post #100
loeg wrote: post #28

Earlier quoted context omitted.

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.

> You're not going up and down the track during an hour record. Here the English language obscures the physics. Sure, the black line on the track is at a constant elevation. But the tire's point of contact is different from the system's center of mass (CoM). CoM is key here. When a rider tilts in the turns, the CoM lowers. In the straights, it raises. So, you _are_ going up and down during the hour record. The questi…

It’s an interesting question & thought experiment! To the degree that it even matters compared to all the other bigger forces, I would put money on riders naturally adjusting for CoM changes by riding slightly higher during the turns; I’d bet they already take approximately the ideal racing line you suggest. I just watched a couple of velodrome rides on YouTube, and it does seem like riders are often closer to the red line during the turn and the black line during the straightaway, statistically, but it’s noisy and would need to be measured.

The CoM’s elevation change on a velodrome track is due to roll rotation around the direction of travel, not to climb & descent. You can’t pedal harder to recover from a lean, so this is a different kind of up and down than straight line elevation changes. It makes sense that work is being done somehow if the CoM moves up and down, but the turns come with necessary changes to the higher moments of inertia anyway that flattening the CoM elevation doesn’t change. I’d speculate that the ideal CoM line might not be flat, in the presence of mandatory high speed banked turns; the fastest line and the line minimizing CoM elevation change might be two different lines. Do also keep in mind that on a velodrome track, a higher elevation line is a slightly larger radius turn & longer travel path. It’s also possible that trying to compensate for CoM elevation change adds as much time as it saves.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#105

Post by magic_smoke_ee »

I was going to say it looked like a Cannondale TT. It was too stiff, unstable, difficult to control, and rode poorly compared to heavier steel frames. Steel is heavier but at least you'll still have teeth left after a ride on a road that isn't perfect like a freshly-asphalted bike path.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#106

Post by danburbridge »

fnord77 wrote: post #18

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.

Ti is difficult to weld - there are a lot of cracked Ti frames out there - often at the welds :( A shame as they (can) look great.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#107

Post by mikeryan »

A_D_E_P_T wrote: post #3

> 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 stif…

How’s it compare to carbon which is the most common high end, lightweight bike material these days?

Re: MIT Aluminum Bicycle Project 1974 (2016)

#108

Post by loeg »

grogenaut wrote: post #44
loeg wrote: post #30

Earlier quoted context omitted.

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, ...…

Check these out https://www.rodbikes.com/profiles/profiles.php?tag=ultra-lig... steel bikes ~13.5 lbs.

Yeah. Very expensive and with significant compromises.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#109

Post by magic_smoke_ee »

briansm wrote: post #72

I find the obsession minimizing bicycle weight funny. It's not the bicycle weight that matters, it's the combined weight of bicycle and rider that counts. Rider weight massively outweighs the relevance of bike frame material, especially in the West where obesity epidemic has biased BMI upwards over the last half century.

Yep. A heavier bicycle is cheaper, less fragile, and also increases the workout effect. As long as a bicycle isn't 20 kg / 50 lbs, what is the real problem? I believe the real goal for lightness is luxury conspicuous consumption to maximize cost using exotic materials like beryllium.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#110

Post by mikeryan »

xnx wrote: post #19

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.

I got down to the bit about Sheldon Brown being Harriet’s husband and was “wait that Sheldon Brown?”

That was when I realized what site I was on.

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