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MIT Aluminum Bicycle Project 1974 (2016)

sheldonbrown.com

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Re: MIT Aluminum Bicycle Project 1974 (2016)

#81

Post by wink »

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.

It's not bike weight per se, but there's also a somewhat direct link between weight and component quality and age. I.e. no one really tests a 20y old bike with current top-end components, no one really puts 10y old groupsets on a 2024 frame.

Yes, rider weight trumps it, but modern bikes in general just ride nicer and most of us who are not pros only test a dozen different bikes at most. It's a hobby, people like to splurge.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#82

Post by impossiblefork »

_yb2s wrote: post #76
A_D_E_P_T wrote: post #13

Earlier quoted context omitted.

> It cracked. > "Kirk Revolution cast magnesium" 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.

Carbon would cause galvinic corrosion in contact with magnesium, and would also visually hide dangerous cracks- I don’t think a carbon wrapped magnesium bicycle would be safe.

If one wants to do that kind of thing it might be better to fill the CFRP with something else-- stiff foam, balsa etc.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#83

Post by ndsipa_pomu »

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.

Weight isn't that important for bike racing unless you're specifically doing hill climbs. Aerodynamics will make more of a difference, so there might be some advantage in having a bit of belly fat to enable a smooth airflow.

Also, heavier riders are generally faster downhill as they have a greater terminal velocity.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#84

Post by ndsipa_pomu »

A_D_E_P_T wrote: post #80
ndsipa_pomu wrote: post #77

Earlier quoted context omitted.

If you're thinking of wrapping a material in carbon fibre, why not just use carbon fibre composite in the first place? Is magnesium stronger than CF for a given weight?

Magnesium, especially a casting, can be something like an order of magnitude cheaper. Carbon fiber is an intrinsically more expensive material, and manufacturing complex engineering parts solely with CF, to high quality standards, is almost an artisanal process.

> Magnesium, especially a casting, can be something like an order of magnitude cheaper.

That doesn't seem to be borne out by bike prices - it's entirely possible to buy a very usable carbon fibre bike for approx £1000 but I can't recall seeing a magnesium framed bike for £100.

Edit: looking at cheap frames on AliExpress, you're not too far off. I saw a magnesium alloy frame for approx £80 and a carbon fibre frame for £350. Not quite an order of magnitude though.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#85

Post by briansm »

tomaskafka wrote: post #78
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.

That’s what I tell myself when picking the bike - just get a competent basic $700-ish bike, and if you want it 2 kg lighter, lose those 2 kg instead of paying thousands.

In evolutionary terms, being taller, fatter and more muscular is advantageous, but in practical terms it's just a lot of extra weight to drag around for a lifetime, along with all the extra calories of energy needed to do so.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#86

Post by ndsipa_pomu »

brudgers wrote: post #38

Every time I’ve visited a Sheldon Brown page, I’ve gone down a rabbit hole. This time it was “Sheldon Brown’s personal bicycles” https://sheldonbrown.com/org/bicycle.html That’s the essence of a great website.

I've only just found out that he suffered from Multiple Sclerosis: https://www.sheldonbrown.com/org/ms.html

Re: MIT Aluminum Bicycle Project 1974 (2016)

#88

Post by Scoundreller »

ndsipa_pomu wrote: post #87
yapyap wrote: post #59

nice story but the ads are awfully annoying, and b4 u suggest an adblocker, I’m on a phone.

Various VPN services provide ad blocking and a phone app e.g. Mullvad

It’s not perfect, but carefully choosing DNS resolvers/profiles can get you a lot of the way there.

Even Mullvad ad-blocking DNS is available for free, no app (and def no account!)

https://mullvad.net/en/help/dns-over-https-and-dns-over-tls

Nice thing is you can set your DHCP to hand this out to all devices.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#89

Post by _yb2s »

impossiblefork wrote: post #82
_yb2s wrote: post #76

Earlier quoted context omitted.

Carbon would cause galvinic corrosion in contact with magnesium, and would also visually hide dangerous cracks- I don’t think a carbon wrapped magnesium bicycle would be safe.

If one wants to do that kind of thing it might be better to fill the CFRP with something else-- stiff foam, balsa etc.

Yes, that is how carbon fiber racing sailboats are made

Re: MIT Aluminum Bicycle Project 1974 (2016)

#90

Post by _yb2s »

A_D_E_P_T wrote: post #79
_yb2s wrote: post #76

Earlier quoted context omitted.

Carbon would cause galvinic corrosion in contact with magnesium, and would also visually hide dangerous cracks- I don’t think a carbon wrapped magnesium bicycle would be safe.

I was just spitballing, but it's possible: First you coat or anodize the magnesium, which I imagine needs to be done in any case. Then you apply a layer of epoxy. Then you wrap in carbon/epoxy. Done properly, there's no direct contact between carbon and magnesium, and you're probably less likely to see corrosion in the Mg-CF composite than you are with magnesium by itself.

The epoxy barrier might work, but in general encapsulated metals are risky because they are impossible to inspect for corrosion and cracking so fail without warning, and the encapsulation can block surface oxide formation which causes crevice corrosion- especially if small amounts of salt and water get in there, which they will over time, even in epoxy.

I’m sure what you are saying could be done- especially to basically add stiffness to key regions of a carbon racing bicycle, but it would be experimental and I would not trust it to last a long time

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