Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

MIT Aluminum Bicycle Project 1974 (2016)

sheldonbrown.com

Post reply on HN
Print view View original

91–100 of 152 posts

Re: MIT Aluminum Bicycle Project 1974 (2016)

#91

Post by ndsipa_pomu »

_yb2s wrote: post #90
A_D_E_P_T wrote: post #79

Earlier quoted context omitted.

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 basica…

> I’m sure what you are saying could be done- especially to basically add stiffness to key regions of a carbon racing bicycle

I reckon it'd be a lot easier to just increase the wall thickness if you want that section of a carbon frame to be stiffer

Re: MIT Aluminum Bicycle Project 1974 (2016)

#92

Post by ndsipa_pomu »

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

Unless you can hide away a 2kg battery/motor combo. (Just joking really as they do scan for hidden motors nowadays)

Re: MIT Aluminum Bicycle Project 1974 (2016)

#93

Post by _yb2s »

ndsipa_pomu wrote: post #91
_yb2s wrote: post #90

Earlier quoted context omitted.

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 basica…

> I’m sure what you are saying could be done- especially to basically add stiffness to key regions of a carbon racing bicycle I reckon it'd be a lot easier to just increase the wall thickness if you want that section of a carbon frame to be stiffer

Not really- even very thick carbon is quite flexible…. It works great for applications where you want that like bendy sailboat masts and front forks on bikes, but it should be cored or replaced with something else if you are looking for stiffness

Re: MIT Aluminum Bicycle Project 1974 (2016)

#94

Post by mtillman »

leoh wrote: post #4

Favorite road bike I’ve ever owned was the aluminum Klein Quantum Race designed by Greg Klein.

I still own a Klein Performance ‘81 and an Adept Comp that has its own amazing story. Love Klein bikes. In fact, I kind of expected this article to be about Klein since it also came from MIT in 1975.

https://en.wikipedia.org/wiki/Klein_Bicycle_Corporation

Re: MIT Aluminum Bicycle Project 1974 (2016)

#95

Post by mtillman »

ndsipa_pomu wrote: post #70
trhway wrote: post #66

aluminum is nice, yet once in a blue moon you get something like this year an aluminum hiking pole broke when i lost my balance on a slippery slope and put a lot of weight on the pole and falling i almost got skewered by it's broken off jagged lower piece. I really want steel poles now, yet can't find them to the point of pondering DYI-ing from some Home Depot steel tubing.

That's a problem with aluminium - no fatigue limit. This means that cyclic loads on an aluminium frame (or pole) will eventually cause it to fail. Steel does have a fatigue limit such that cyclic loads below that threshold won't cause eventual failure. There's some good info on bike frame materials here: https://bike.bikegremlin.com/11144/bicycle-frame-materials-e...

Wasn’t this solved by Klein?

Re: MIT Aluminum Bicycle Project 1974 (2016)

#96

Post by giamma »

twic wrote: post #7
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…

There was a magnesium bike frame back in the '90s, made by Kirk: https://www.elmycycles.co.uk/m21b0s365p4804/1992-Kirk-Revolu... https://www.bikeforums.net/classic-vintage/1279777-kirk-prec... https://www.independent.co.uk/news/uk/magnesium-in-frame-to-... https://www.flickr.com/photos/11521783@N05/albums/7215764801... A friend had one. It cracked.

Vaast bikes [0] makes magnesium bikes today, I own one (A/1 gravel) and it's a very pleasant ride.

[0] https://www.vaastbikes.com/

Re: MIT Aluminum Bicycle Project 1974 (2016)

#97

Post by ndsipa_pomu »

_yb2s wrote: post #93
ndsipa_pomu wrote: post #91

Earlier quoted context omitted.

> I’m sure what you are saying could be done- especially to basically add stiffness to key regions of a carbon racing bicycle I reckon it'd be a lot easier to just increase the wall thickness if you want that section of a carbon frame to be stiffer

Not really- even very thick carbon is quite flexible…. It works great for applications where you want that like bendy sailboat masts and front forks on bikes, but it should be cored or replaced with something else if you are looking for stiffness

That doesn't match with my experience. I've got a carbon fibre road bike and some parts of the frame are remarkably stiff whereas other areas such as the handlebars have noticeable flex.

It can be surprising to people just how tough/strong carbon fibre parts can be - here's Danny MacAskill's destructive testing of some CF wheels: https://www.youtube.com/watch?v=VfjjiHGuHoc

Re: MIT Aluminum Bicycle Project 1974 (2016)

#98

Post by ndsipa_pomu »

mtillman wrote: post #95
ndsipa_pomu wrote: post #70

Earlier quoted context omitted.

That's a problem with aluminium - no fatigue limit. This means that cyclic loads on an aluminium frame (or pole) will eventually cause it to fail. Steel does have a fatigue limit such that cyclic loads below that threshold won't cause eventual failure. There's some good info on bike frame materials here: https://bike.bikegremlin.com/11144/bicycle-frame-materials-e...

Wasn’t this solved by Klein?

No

Re: MIT Aluminum Bicycle Project 1974 (2016)

#99

Post by xpe »

xpe wrote: post #22
loeg wrote: post #12

Earlier quoted context omitted.

Yeah, Sheldon mentions it in this article. I don't think those mods helped. Weight has no impact on sustained speed.

> Weight has no impact on sustained speed. 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.

Any bump results in some energy transfer. In the case of small enough bumps and tires at ideal pressures, most energy is returned, but not all. These losses accumulate. The question is "how much does it add up to?" This is why I recommend using the phrase "negligible effect" instead of "no effect".

Re: MIT Aluminum Bicycle Project 1974 (2016)

#100

Post by xpe »

loeg wrote: post #28
xpe wrote: post #22

Earlier quoted context omitted.

> Weight has no impact on sustained speed. 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.

> 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 question now becomes: how much effect does this elevation change have?

It is one thing to be aware of the effect, run the calculations, and find the result is negligible. Has anyone done this? That would be an interesting analysis, and I'd like to see it.

With this in mind, I will make another claim: for a particular rider, there is an ideal line around a velodrome that would minimize center-of-mass elevation change. This line would be faster than the current black line. How much faster? This would be a fun simulation problem.

Another interesting connection: center of mass and bicycling explains why pumping works on a BMX track, a pump track, a trail, and so on. (There are other mainstream explanations, but I think the CoM explanation is the most elegant.)

Post reply on HN