Hacker News Reader

Comment by dexwiz | Hacker News Reader

The article cites a race where the bikes were ~50 and 36 pounds. That sounds like a lot. Even a cheapo bike from Walmart is half that. But over time, its going to be the bearings that suck the most energy. I wonder what those were like compared to today.

View on HN

In the late 1980s, early 1990s, sub-30 lbs was the reference for a high-quality off-road bike. That'd be aluminum alloy rims, steel frames (cro-mo alloy) and aluminum bars/stems/seat-posts. A principle that applies at all times (1800's, 1900's, 2000's), is that rotational mass is what kills you; Roughly, if you can save 1 lb on the wheels, or 1.5 lbs on the frame, save on the wheels. It's mass that has to be accelerated/decelerated, versus (eg) the frame, which is 'static'.

Edit: qualify "at all times", "late 80s, early 90s"

http://thisoldbridgestone.com/tag/mb-1/ - I had one of these from '92, I think, and it weighed 24 pounds, roughly. And that's a mass produced bike that was high end, but not top of the line by any means. Somehow I find it kind of sad that today, they weigh about the same because of all the stuff they've added to them.

Bridgestone was making highly regarded bikes, mass produced or not. Example, a state-of-the-art rig would be a Ritchey P-23 (c. ~1990), so named because it was a project to make a 23lb bike, which was a Big Enough Deal to name the bike after the project. I feel like the bikes[0] I[1] raced[2] at the time ($1800 - $2600, not adjusted) were in the 25-26lb range (19.5 - 20.5" frames). The very light bikes (like a P-23) were contraindicated for heavy, non-expert riding. Working at a high-end bike shop around that time, I saw them[3] come back in pieces.

[0] http://www.retrobike.co.uk/forum/download/file.php?id=35724

[1] http://www.retrobike.co.uk/forum/download/file.php?id=258229

[2] http://i41.tinypic.com/j9y5ug.jpg

[3] http://fcdn.mtbr.com/attachments/vintage-retro-classic/12540...

> they weigh about the same because of all the stuff they've added to them

Buy a decent frame and build your own bike. I have three bikes -- MTB, hybrid and one I made myself. The homemade one is easily my favourite, and I think it's the better bike. You get to decide what's important to you rather than the manufacturer. Road wheels with bullhorn bars and 3 cogs at the front? No problem, I can do what I like.

Can you explain the physics of rotating mass savings being more important? The top of the wheel moves twice as fast as the bike, but the bottom of the wheel doesn't move at all so don't they balance out? The frame isn't static - you still have to accelerate it frame along with the wheels when you're speeding up.

If your route has a lot of uphill, then I'd expect that 1.5:1 ratio to get closer to 1:1 where the work you do is more fighting gravity than inertia.

It takes energy to make things rotate:

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

The wheels have a rather large diameter and go pretty quickly. Both diameter and angular velocity are quadratic terms. You could now do the math to see how much energy it takes to accelerate a bike to a given speed.

But you're right, going uphill or at steady speed completely changes the picture.

Here are some articles[0][1] -- and to be clear, the tone of the first (bicycle) article is appropriately "fussy". One person who gets groceries on their bike may not notice, but a competitive racer might notice. So whether it matters (enough) depends on the situation. With suspended bikes, wheels are also never part of the "sprung" weight; minimizing unsprung weight in suspension is always beneficial. I don't have metrics for how many grams deliver $x performance, though.

[0] http://velonews.competitor.com/2012/06/bikes-and-tech/techni...

[1] http://www.tuneruniversity.com/blog/2011/04/part-i-why-wheel...

Rotational mass is important if you're doing lots of accelerations, but for almost all riders the real killer is rolling resistance. The difference between good tyres and bad is light and day. And note, narrower+harder != better... tests have shown that wider tyres running low pressures but with supple side walls can be as fast or faster than narrower tyres, and are much more comfortable to boot.

> for almost all riders the real killer is rolling resistance

Aerodynamic resistance becomes greater than rolling resistance very early. See eg. http://www.sheldonbrown.com/rinard/aero/formulas.htm

You may argue that people riding upright on city ("dutch") bikes make up the majority of bike riders, but their possibly heavy-rolling tires are made up for their aerodynamically pessimal riding posture!

(Of course often it's easier to do something about rolling resistance than aerodynamics, despite being a smaller component)

No. Cheapo adult bikes are typically 30 to 40 lbs. The difference is that these modern cheapies are built with thickwall aluminum or steel tubing to avoid lawsuits and are burdened with modern accoutrements like shifters and brakes. The 1874 race bikes are penny-farthings with very little framing and likely thinner tubes than cheap steel bikes of today.

Having a number of bikes, getting a bike sub 20b, you are hitting upper end even on road bikes.

My dual suspension carbon mountain bike is ~23-24lb w/ pedals.

My steel touring bike, well, it's a little hefty.

But does the sub 20 lb bike really gain you a lot? For reference, I weight 220 lbs -- so the difference between and 18 lb and a 30 lb bike really doesn't seem like a lot. I guess what I'm asking, does losing 5 lbs on a bike equal losing 5 lbs on the rider? Logically this would seem the case.

But there is probably one other factor to consider -- the lighter bike is more expensive, therefore probably has better components (chain/shifters/bearings/tires/gears), which makes it feel smoother. And if it feels better, you will get the perception of higher speed or less effort.

I've only ridden super-light bikes rarely. Still, among the ones that I've ridden, lighter bikes seem more responsive and fun to ride. Is it a big deal? Probably not. Will it win me a race? No, that would still require a much better motor.

And like you say, better components can make a difference, within reason.

The main reason I prefer a lighter bike is for when I need to carry it up some stairs or something like that. For most everyday riding I don't think weight matters much.

I feel the same about carrying the bikes up stairs :-)

However there is a noticeable difference in riding as well, unless you ride only on short distances.

You can simulate the difference on the same bicycle so the comparison is not tainted by different tires and mechanical components. You can add 5 kg (or 10 pounds) here and there or even in a backpack (but it will harm your performance in other ways). Maybe don't put weight on the steering/front wheel because that will make for a difficult handling. You can use water, so you can release it at any time and feel the difference.

You'll notice that with the extra weight you accelerate less and climb worse. All sort of disadvantages derive from that. If you do 100 km and you have a choice, you'll go for the lighter bicycle. Unfortunately that means a lighter purse as well, maybe much lighter.

For those of us who ride road bikes, yes sub 20lb makes a big difference. My Fiancee's road bike with Sora components is just under 19lbs and that's pretty basic as far as a road bike goes.

It gets a lot more expensive once you go sub 14lbs, and very very expensive sub 10.5lbs or so. (20k+)

It's mostly about the rider, but when you get to the elite guys, every little bit counts. You and I probably have 5 pounds to lose; they don't:

http://c.files.bbci.co.uk/16E6F/production/_84270839_froome....

It's interesting.

Cycling is unlike any human powered sport except iceskating in that aerodynamics play a huge role. That means packs are the default state of play, except in a few limited circumstances.

One of those cases is climbing, where speeds can be low enough that a few pounds makes a big difference.

Sort of.

When I was towing an empty 20+ lb trailer, and the bike +rider was in the 210lb range (so, 10% of the mass) I was about 10% slower than sans-trailer. Towing a trailer + 25lb kid was about another 10%.

A lighter bike _may_ feel different, but whether it's weight or something else, or even placebo is up for discussion. It's hard to tell frame weights. 20 years ago, I ran some blind testing where we put weighted waterbottles in a frame, one with lead, one with glass beads, and one empty. 5 trials, A/B, which one was heavier. IIRC, adding 5 lbs of lead was noticable to almost everyone, but the difference between 2.5 and 5 lbs was only noticeable to the frame builder.

Lighter bikes don't make you faster in steady speed riding on a perfectly flat surface. The hour record bikes are optimized for everything but weight.

But we are very bad at judging absolute speed without technical assistance, while being quite sensitive to acceleration. Therefore, a slight increase in acceleration for a given effort (or decrease in effort for a desired acceleration) is very noticeable, while an increase in absolute speed would not. So a lighter bike will feel noticeably faster (even though it isn't), while different aerodynamics (e.g. "faster" clothes that give a lot more improvement in absolute speed than a weight difference, even for weak riders) might give a clear advantage on the clock, but you won't be able to notice it while riding.

Light bikes just feel fast, very much so actually. It's a powerful illusion that only gets stronger because it is supported by those few specific situations (stop and go, races with tight corners, all that climbing road cyclists love) where the weight also matters objectively.

Given that wheel diameters are given, these were likely penny-farthing models: direct drive, one large wheel, one small, no chain.

See the 1874 racing bike pictured in this PDF (p. 4): http://library.la84.org/SportsLibrary/JSH/JSH1999/JSH2603/JS...

Which might have weighted 36lb https://en.wikipedia.org/wiki/Penny-farthing#Construction

Reply on news.ycombinator.com