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

131–140 of 152 posts

Re: MIT Aluminum Bicycle Project 1974 (2016)

#131

Post by david-gpu »

matsemann wrote: post #127
cenamus wrote: post #126

Earlier quoted context omitted.

So it only matters on basically every classic non time trial race?

With the speeds the pro's climb these mountains, aero is still a big deal. For you and me slogging along it's almost all weight that matters. But not for the pros.

Keep in mind that arodynamic drag is not a function of ground speed, but airspeed. If you ride slowly in a relatively windy place, your airspeed can easily be twice of your ground speed.

That said, given how many of us are overweight, worrying about a couple of kilos on the bike is funny talk anyway.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#132

Post by loeg »

grogenaut wrote: post #121
loeg wrote: post #108

Earlier quoted context omitted.

Yeah. Very expensive and with significant compromises.

could you expand? I get the expensive part, but they're also hand built customs so...

Rim brakes are not great in wet conditions and limit tire sizes to about 28mm. Lightweight steel tends to be flexy and susceptible to dents.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#133

Post by loeg »

eftpotrm wrote: post #124
cenamus wrote: post #54

Earlier quoted context omitted.

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

I remember hearing Callum Skinner talk about the British track team preparing for the Olympics, and how the biggest problem they had was strength - I remember the number 2400 for their best track sprinters, I forget if that was in watts or newtons but either way it's a massive force and they were snapping frames. The discipline of cycling that's the most weight-motivated is hill climbing. Track cycling really doesn't…

2400W is plausible for a world class track sprinter.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#134

Post by ndsipa_pomu »

magic_smoke_ee wrote: post #112
ndsipa_pomu wrote: post #83

Earlier quoted context omitted.

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.

> have a greater terminal velocity No, unless they're Russian, they're not free falling. They have greater potential energy. And also increased traction, increased rolling resistance, and increased losses in wheel bearings and drive components due to friction.

Terminal velocity can still apply when cyclists are going downhill. Essentially it's the speed that a cyclist will reach when the gravitational force is equal to rolling resistance (roughly proportional to speed) plus the air resistance (roughly proportional to the square of speed) assuming that they're just free-wheeling and not pedalling. If two cyclists have a similar air resistance, but different weights, then the heavier cyclist will reach a quicker speed. There's the argument that a heavier rider will be bigger and thus have more air resistance, but that effect is smaller than the weight difference. (NB. this can be trivially tested).

Re: MIT Aluminum Bicycle Project 1974 (2016)

#135

Post by ndsipa_pomu »

david-gpu wrote: post #123
ndsipa_pomu wrote: post #65

Earlier quoted context omitted.

I don't believe that the frame material makes much difference to comfort. The part that can deflect/absorb bumps and vibration the best is the tyre. So the answer to your question is bigger tyres at lower pressures.

Yeah, whenever I hear people talk of the properties of bike frame materials it reminds me of audiophiles: plenty of strong opinions backed by a remarkable absence of data. A typical bike frame follows a truss structure: stiff and unyielding by design. Vertical compliance is going to be found elsewhere: tires, exposed seatpost, chamois/saddle, fork, handlebar, tape. Yet, how many roadies do you find talking about susp…

Yeah, suspension seatposts can provide 20mm of vertical compliance (varies for different models) which is more than you'd get with 28mm width tyres. I have tried a split stem suspension seatpost, but found that that particular design wasn't great as it was difficult to set the saddle up so that it didn't end up tilting as the two parts of the seatpost moved within the frame. I currently use just a standard carbon fibre seatpost that provides some compliance, but isn't a "suspension" type.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#136

Post by justinator »

eigart wrote: post #67

Just an anecdote thats been horrifying me for the last week since Klein is mentioned. I learned last week that my colleague bought a commuting bike from an old friend. A true once in a lifetime barn find. Mid 90s Klein Attitude, only used for a few weeks before being stored in the barn until 2023. My colleague is currently putting it through its second winter on salted, snowy roads.

I'd much rather see a bike used for a purpose than a bike lost in the back of a barn!

What's the alt. timeline for the bike? Stored as a collectors item?

Ships in the harbor and all.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#137

Post by stevage »

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…

Yeah I was curious about the weight thing too. The hour record is probably the event in which weight matters the least, since there's no acceleration and no hills.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#138

Post by dartharva »

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.

Depends on what you're using the bike for. If it is for work or transport (as it used to be for paperboys and delivery gigs a few decades ago), you'd want it to be as smooth and light as possible.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#139

Post by wiether »

magic_smoke_ee wrote: post #109
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.

> and also increases the workout effect

If you push 300W on a 5kg bike or 20kg bike, the "workout effect" will be the same.

At the end of the day, if you are looking for "workout effect", it means that you're trying to achieve something, like winning races or going faster.

And for a given rider, with a certain weight and certain physiological abilities, they will go much faster on a 5kg bike than on a 20kg bike.

There is a whole world between $2k ones. Weight being an important part. Not only because it reduce the total weight of bike + rider, but also because a 5kg bike behave in a very different way than a 20kg.

It's like saying that cooking with a chef knife is the same as cooking with a sword.

Sure, after a certain point, the race for removing a few grams here or there is a luxury and many people tend to believe that spending $$$ on a lighter bike will fix their lack of fitness.

But modern bikes provide a completely difference than the old, heavy ones.

Re: MIT Aluminum Bicycle Project 1974 (2016)

#140

Post by kevin_thibedeau »

sudosysgen wrote: post #26
kevin_thibedeau wrote: post #21

Earlier quoted context omitted.

You slow down incrementally between every power stroke.

A heavier bike would slow down less. At the end of the day the energy is lost to friction.

Wind resistance is the primary force slowing you down at speeds where riders care about such things. The tiny micro-accelerations after every dead zone add up in spent calories when you have a more massive bike+rider system.
Post reply on HN