Lighter bikes, not faster to commute on...

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TheKrikkitWars
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Lighter bikes, not faster to commute on...

Postby TheKrikkitWars » Tue Dec 14, 2010 1:05 pm UTC

BMJ Article
BBC Article about BMJ article

I'm skeptical of the applicability of the results across broad scenarios as carbon bikes have been associated with a measurable advantage in several racing disciplines (though I'd never own a carbon bike, but that's a whole other issue), but the author clearly never intended that conclusion to be drawn...

I can see a definite method of action for a substantially better piece of equipment not making a massive difference in a scenario like cycling to work where you're (hopefully) going at a leisurely pace.

However this also highlights another issue, the poor quality of science reporting in the media... That article adds feck all to the press release from the BMJ apart from tacking on a largely tangential bit to the bottom, where it infers that because this trial has found a slightly heavier steel framed road bike isn't much slower than a Mid-Range carbon one, that you might as well just switch to a mountain bike.

Anyway, Evidence Based Medicine for the win once more!
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Re: Lighter bikes, not faster to commute on...

Postby JBJ » Tue Dec 14, 2010 2:00 pm UTC

The article wrote:While a 30% reduction in cycle weight may seem large, concludes the author, the results show that there is no measurable difference in commuting time between his light and heavy bikes. He adds that “a reduction in the weight of the cyclist rather than that of the bicycle may deliver greater benefit at reduced cost”.
No shit, Sherlock. This trial fails the common sense test. Not being familiar with the actual route, I still feel pretty confident in assuming that he was sharing the roadway, had to cross intersections, and otherwise cooperate with the normal flow of traffic. Those factors would have had more impact on time than a 10lb difference in weight. I mean, if I randomly chose between a 3 ton truck or a 500 lb. motorcycle for my commute I would have nearly identical times for both despite the truck being 12 times heavier.
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Re: Lighter bikes, not faster to commute on...

Postby Griffin » Tue Dec 14, 2010 2:05 pm UTC

I know I prefer mountain bikes or cross bikes for my commute. That's because they are tougher, though, and a bit more versatile. The same reason some people commute in a pickup truck, I assume.

You might do a bit more work to get where you're going, but the improvement in options is worth it for some.

That said, this article is total crap. Of course it takes about the same amount of time - people go at the speed they are used to even if it is suboptimal, and have to deal with the realities of traffic and other such things! But a good bike is definitely way more pleasant to ride than a crappy one, and without good gear changing cycling in many areas is terribly unpleasant. Good bikes aren't about more speed (unless your a racer), they are about a better ride.

Edit: Haha, I find it amusing that we both mentioned the truck thing. :P

I also want to add that if you are biking for your health, a lighter bike means less work means less health benefit.
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Re: Lighter bikes, not faster to commute on...

Postby Technical Ben » Tue Dec 14, 2010 2:47 pm UTC

Epic fail is epic. Even worse it's epically reported on. :lol:

You do not buy a lighter bike to commute faster. Do you buy a lighter car to drive faster? As my little mini weighs less than a Veyron. The mini should be quicker right?
You get a lighter bike, because it does not use as much energy. Granted, there is probably an optimal weight. I am not sure if that was more of what the experiment was looking for. However, a half ton bicycle is going to be harder to pedal than a ten kilo one.

In other news, wellies do not keep your hair dry, and larger TVs do not play films quicker.
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Re: Lighter bikes, not faster to commute on...

Postby johnny_7713 » Tue Dec 14, 2010 3:24 pm UTC

JBJ wrote:
The article wrote:While a 30% reduction in cycle weight may seem large, concludes the author, the results show that there is no measurable difference in commuting time between his light and heavy bikes. He adds that “a reduction in the weight of the cyclist rather than that of the bicycle may deliver greater benefit at reduced cost”.
No shit, Sherlock. This trial fails the common sense test. Not being familiar with the actual route, I still feel pretty confident in assuming that he was sharing the roadway, had to cross intersections, and otherwise cooperate with the normal flow of traffic. Those factors would have had more impact on time than a 10lb difference in weight. I mean, if I randomly chose between a 3 ton truck or a 500 lb. motorcycle for my commute I would have nearly identical times for both despite the truck being 12 times heavier.


Not to mention that a probably fairly significant amount of the work you have to do when cycling is to overcome air resistance / drag, on which the weight of the bicycle will have exactly zero influence. Also a 30% reduction in bicycle weight will only translate into about a 3-6% percent reduction in the mass of the bicycle-driver system, which is what's important for determining the total work you have to do. Enough to make the difference in world/olymipic level competitions, but not really useful when you're commuting.

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Re: Lighter bikes, not faster to commute on...

Postby Zamfir » Tue Dec 14, 2010 3:29 pm UTC

You get a lighter bike, because it does not use as much energy.
That's just as dubious. Presumably, if it save you a noticeable amount of energy, you would cycle a bit faster too. That's rather different from cars, where all cars can easily hit the speed limit. Also, a Veyron has a higher hp-to-weight ratio, so that is the one most comparable to a light bike. Except that a Veyron has several times more HP per kilo, while a lighter bike gives you only a few percent more power per kilo.

IME soft tires and a badly oiled chain make a real difference to the worse. Toeclips make you go noticeably faster, but for the rest the big advantage in speed of a racing bike is more in the way you sit on it, that encourages you to cycle faster.

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Re: Lighter bikes, not faster to commute on...

Postby Technical Ben » Tue Dec 14, 2010 4:17 pm UTC

It appears I massively over estimated the gain there. It's only 6%. My intuition was correct though, it is a benefit, although too small. :P
In tests, it's around 30 seconds for 5 pounds for a 20 min ride. So only worth it for racing bikes, where every second counts. On a commute your not going to see that 30 seconds with navigating traffic. Not is it really any benefit.
That said, the only reason I did go for a "light" bike is so I can lift it in and out of the back of the car or garden with out too much trouble.
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Re: Lighter bikes, not faster to commute on...

Postby The Reaper » Tue Dec 14, 2010 4:46 pm UTC

Spoiler:
Image
Lightcycles<3

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Re: Lighter bikes, not faster to commute on...

Postby frezik » Tue Dec 14, 2010 4:48 pm UTC

Technical Ben wrote:Do you buy a lighter car to drive faster? As my little mini weighs less than a Veyron. The mini should be quicker right?


Possibly quicker, but not faster. In drag racing, "quick" refers to acceleration, and "fast" refers to top speed. The Veyron is quick, but it's extremely heavy, and there are some smaller cars (like the Ariel Atom) that are even quicker.

Top speed isn't affected by weight, just drag coefficient and torque to the ground.
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Re: Lighter bikes, not faster to commute on...

Postby Endless Mike » Tue Dec 14, 2010 4:51 pm UTC

Technical Ben wrote:You do not buy a lighter bike to commute faster. Do you buy a lighter car to drive faster?

All other things equal, yes. If your Mini was 10% lighter, it would be faster. It might not impact a commute much, however.

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Re: Lighter bikes, not faster to commute on...

Postby Azrael » Tue Dec 14, 2010 5:28 pm UTC

frezik wrote:Top speed isn't affected by weight, just drag coefficient and torque to the ground.
Top speed is typically considered a function of overall horsepower, since it's the product of both torque and speed. Having low drag and lots of torque doesn't get you very far unless you have sufficient power.

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Re: Lighter bikes, not faster to commute on...

Postby TheKrikkitWars » Tue Dec 14, 2010 6:22 pm UTC

I'd like to see this done again with varying weights of wheel and tyre combination, as the rolling weight of the bike makes a much much bigger contribution to determining the speed than that of the non-rotating bits.

To all the people slagging this off as being fail somehow, why? It provides evidential backing to one hypothesis in a scenario where one can argue that both hypotheses are either the "intuitive" or "counter-intuitive" one depending on your view of the world (and experience of buying extremely light bicycles).
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Re: Lighter bikes, not faster to commute on...

Postby The Reaper » Tue Dec 14, 2010 6:35 pm UTC

TheKrikkitWars wrote:I'd like to see this done again with varying weights of wheel and tyre combination, as the rolling weight of the bike makes a much much bigger contribution to determining the speed than that of the non-rotating bits.

This is where I like you to a flash program written by someone to genetically evolve bike designs. Alas, it does not work.
http://www.boingboing.net/2008/12/08/ge ... hm-ev.html
But, never fear. Program your own, evolve a bike, and compare its weight to standard bike weights. :3

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Re: Lighter bikes, not faster to commute on...

Postby JBJ » Tue Dec 14, 2010 7:27 pm UTC

TheKrikkitWars wrote:To all the people slagging this off as being fail somehow, why? It provides evidential backing to one hypothesis in a scenario where one can argue that both hypotheses are either the "intuitive" or "counter-intuitive" one depending on your view of the world (and experience of buying extremely light bicycles).

What he did was certainly valid within the scope of his commute, and his commute only. It's of little use to anyone else, because he didn't account for the variables that would influence the outcome. Notably the conditions that would affect his average speed (traffic, intersections, etc...) He also did not vary the length of his commute. He rode 27 miles (13.5 each way) presumably following the same route each time. What if a lighter bike actually does make a significant difference for commutes of less than 10 miles? Or 5 miles? Or 40+ miles? No issues with the method he took to determine, for himself, whether his investment in a lighter bike paid off or not. Applying the same methods to commutes as a whole is flawed, and so the conclusions he and others have drawn from his experiment are flawed.

Edit - also to add that using a high performance racing bicycle for commuting is akin to using a formula one car for going to the grocery store. You're most likely never going to realize the full potential of the vehicle under those conditions.
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Re: Lighter bikes, not faster to commute on...

Postby Zamfir » Tue Dec 14, 2010 8:59 pm UTC

TheKrikkitWars wrote:I'd like to see this done again with varying weights of wheel and tyre combination, as the rolling weight of the bike makes a much much bigger contribution to determining the speed than that of the non-rotating bits.

When you say speed, do you mean constant speed, or the average speed over a trajectory, including accelerations and stops? Weight has some small effect on the first, because rolling resistance will be higher for heavier bikes, but that is not related to rolling or not rolling. Light wheels do of course matter a lot in acceleration, and bike nuts I know tend to spend ridiculous amounts on light wheels. But the psychological effect of faster acceleration is much gretaer than the real effect on your average speed. A lighter bike, and especially a bike with lighter wheels feels much faster, because accelerations are the moments you are most aware of your bike. But in practice, you spend an almost negligable amount of time on quick accelerations,a nd saving a few seconds off doesn;t matter much.
To all the people slagging this off as being fail somehow, why? It provides evidential backing to one hypothesis in a scenario where one can argue that both hypotheses are either the "intuitive" or "counter-intuitive" one depending on your view of the world (and experience of buying extremely light bicycles).

To me, the main point is that 4 kilos on the total weight just isn't much, and in the best case the effect would still be lost in the noise of the experiment. The only way 5% or so of weight should have a noticable effect was if his commute consisted of a steep climb both ways, without traffic or anything to add noise

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Re: Lighter bikes, not faster to commute on...

Postby clumsy_culhane » Tue Dec 14, 2010 11:08 pm UTC

As others have said, its a horribly written article. As a cyclist myself, I can understand how the time commutes took would not be affected very much by bike weight, as stopping for lights, pedestrians etc slow you down a lot, so the small gains in top speed (gained my the better position on a racing bike) are reduced. The lighter weight really only comes into play on steep inclines. I recently bought a mid-range racing bike after riding a sturdy, but heavy hybrid, and the difference for long range (100km+) rides was very very noticeable, but for a quick dash to the shops, both are about equal, purely because the gains given by the racing bike only really become apparent as you become more and more fatigued (toeclips/cleats help a lot here), and as your speed increases.

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Re: Lighter bikes, not faster to commute on...

Postby dedalus » Tue Dec 14, 2010 11:37 pm UTC

Putting it out there; if the average person + bike weighs ~80kg, and there's a 4kg difference - that's 5%, which is a much more important figure to quote then the 30% weight difference between bikes. This being combined with facts already mentioned regarding the real cause of lost time in commuting, and yeah.
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Re: Lighter bikes, not faster to commute on...

Postby masher » Tue Dec 14, 2010 11:50 pm UTC

The Reaper wrote:
Spoiler:
Image
Lightcycles<3


http://www.wired.com/autopia/2010/11/ge ... ght-cycle/

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Re: Lighter bikes, not faster to commute on...

Postby Sero » Wed Dec 15, 2010 12:41 am UTC

masher wrote:
The Reaper wrote:
Spoiler:
Image
Lightcycles<3


http://www.wired.com/autopia/2010/11/ge ... ght-cycle/


I...okay, there's currently a war on. Half of me is saying 'DUDE that is so COOL'. The other half is being all reasonable and practical and saying 'sure, but it looks reeeeally awkward to ride. Downright uncomfortable, even.'
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Re: Lighter bikes, not faster to commute on...

Postby Technical Ben » Wed Dec 15, 2010 8:24 am UTC

frezik wrote:
Technical Ben wrote:Do you buy a lighter car to drive faster? As my little mini weighs less than a Veyron. The mini should be quicker right?


Possibly quicker, but not faster. In drag racing, "quick" refers to acceleration, and "fast" refers to top speed. The Veyron is quick, but it's extremely heavy, and there are some smaller cars (like the Ariel Atom) that are even quicker.

Top speed isn't affected by weight, just drag coefficient and torque to the ground.

(Note I said "fast" not "quick" but none the less)
Nope. 2.4 for a Veyron V 2.9 on an ATOM.
(google fu later)
Oh, appears you are right. But only after market testing. Or they must of changed something. [edit] Seems they upgraded from a 2l engine to a 3l?) :P
http://en.wikipedia.org/wiki/List_of_fa ... celeration

Still not always the case.

Endless Mike wrote:
Technical Ben wrote:You do not buy a lighter bike to commute faster. Do you buy a lighter car to drive faster?

All other things equal, yes. If your Mini was 10% lighter, it would be faster. It might not impact a commute much, however.


Which is exactly what I said! Come on people! Gah! [edit] Oh, you are agreeing. Was not sure if you were disagreeing with me?
Last edited by Technical Ben on Wed Dec 15, 2010 1:50 pm UTC, edited 1 time in total.
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Re: Lighter bikes, not faster to commute on...

Postby johnny_7713 » Wed Dec 15, 2010 9:17 am UTC

As noted in the OP that BBC article is really, really bad. I don't know how many of you read it, but it contains gems like: 'And [cycling] can save a fortune. Or can it?' Well, yes, yes it can, since the rest of your article is about someone who showed that you don't need to get a really expensive bike for commuting to your work since a £50 one will work just as well :roll:

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Re: Lighter bikes, not faster to commute on...

Postby Sockmonkey » Wed Dec 15, 2010 6:26 pm UTC

The Reaper wrote:
Spoiler:
Image
Lightcycles<3
Damn you for making me giggle at a silly pun.
Personally, I might spend more on better wheels that that will still be light but won't warp if I hit a curb wrong but that's pretty much it. I'm not gonna use 21 gear ratios. I just want 6 or 7 with the same range as the 21 so I have only one shifter/derailer to worry about. Granted, a light bike would be pretty nice to have when I need to lift it over something too tall to ride over but sticking on a couple good handholds would do just as well. Basically, I'm far more concerned with it getting me where I'm going than in how fast it gets me there.


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