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Does bike weight really matter
« on: May 23, 2012, 07:59 »


Quote
Dear Lennard,
Does bike weight really matter?

I’m about to invest in a better bike now that I’m taking riding more seriously, and I’m looking at the different options depending on the frame materials.

I happen to be an engineer, so I wondered how much bike weight actually matters when climbing. Say that I’m going up a climb that can be as steep as 20 percent in a given moment, the role weight plays can be calculated using basic math (see the graph, where w= bike weight and d= weight drag, as if someone is pulling you from behind the bike).

The actual weight drag difference between a heavy steel bike (like mine, at 29 pounds) and a top of the line “lightweight” carbon fiber bike (say 17 pounds?) is actually just a couple pounds, and in a very steep climb. In lower grade climbs the weight drag is just a fraction of a pound.

So… unless a rider is planning to lift the bike over his/her shoulders, I don’t see the extra $2K investment justified in the bike weight alone. (I can just carry less water when climbing.) I guess inertia plays a role in competitive situations (a lighter bike helps provide faster acceleration… I guess we can calculate if this actually matters as well!!).

Every place I look recommends “getting a lighter bike if you live in a mountainous area.” Is this a myth or am I overlooking anything?
—Miguel
answer here plus the links made in the answer in under

http://velonews.competitor.com/2012/05/bikes-and-tech/technical-faq/tech-faq-does-bike-weight-matter_220429

Dear Miguel,
The lighter bike will climb faster if you put out the same power. Whether the amount faster it is matters enough to you to spend the big dollars is the question.

liked that.............

weight on the Alpe

http://www.training4cyclists.com/how-much-time-does-extra-weight-cost-on-alpe-dhuez/

http://middleagecyclist.blogspot.se/2011/09/weight-matters-study.html

weight or inertia of course it makes a difference but does it matter enough for a average punter and here a question I ask myself why do you ride ?- fitness , lose weight or to be under 40 world Champion or even over  - if it is the 1st 2 then weight or increased inertia is positive.

so ask your LBS for heavy components - something to think about
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    Re: Does bike weight really matter
    « Reply #1 on: May 23, 2012, 08:09 »

    answer here plus the links made in the answer in under

    http://velonews.competitor.com/2012/05/bikes-and-tech/technical-faq/tech-faq-does-bike-weight-matter_220429

    Dear Miguel,
    The lighter bike will climb faster if you put out the same power. Whether the amount faster it is matters enough to you to spend the big dollars is the question.

    liked that.............

    weight on the Alpe

    http://www.training4cyclists.com/how-much-time-does-extra-weight-cost-on-alpe-dhuez/

    http://middleagecyclist.blogspot.se/2011/09/weight-matters-study.html

    weight or inertia of course it makes a difference but does it matter enough for a average punter and here a question I ask myself why do you ride ?- fitness , lose weight or to be under 40 world Champion or even over  - if it is the 1st 2 then weight or increased inertia is positive.

    so ask your LBS for heavy components - something to think about

    All that science is way too complex for me. But the one thing none of these sources mention is psychology. I think that accounts for a strong proportion of the argument in favour of less weight. You think you have even a small advantage and you ride to that effect. ;)

    Let's also look at the inverse - though again I lack the scientific nous to answer the question - in terms of safety on long and technical descents, do lighter bike weights matter there too?
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    just some guy

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    Re: Does bike weight really matter
    « Reply #2 on: May 23, 2012, 08:24 »
    All that science is way too complex for me. But the one thing none of these sources mention is psychology. I think that accounts for a strong proportion of the argument in favour of less weight. You think you have even a small advantage and you ride to that effect. ;)

    Let's also look at the inverse - though again I lack the scientific nous to answer the question - in terms of safety on long and technical descents, do lighter bike weights matter there too?

    much more complex

    more weight of bike equals - faster speed

    but more weight would also mean greater friction - downward force - as they talk about in F1 which may mean better cornering

    then there is the flex or stiffness of the heavier bike v´s lighter too look at

    weight distribution would also need to be looked at
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    Re: Does bike weight really matter
    « Reply #3 on: May 23, 2012, 08:25 »
    I agree re placebo effects

    but then it depends on the question you are asking

    is it to get fit, lose weight or ..

    if it is the lighter equals easier - negative  O0
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  • just some guy

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    Re: Does bike weight really matter
    « Reply #4 on: May 23, 2012, 08:46 »
    there is some stuff to consider in this video

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  • just some guy

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    Re: Does bike weight really matter
    « Reply #5 on: May 23, 2012, 08:59 »
    Friction would be closest to a normal force vector yes but my meaning that without the downward force you do not have increase in friction - sorry

    p= F/A  so the area is important but so is the downward force

    but being engineer type I am sure I will be schooled
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  • ram

    Re: Does bike weight really matter
    « Reply #6 on: May 23, 2012, 09:06 »
    Mine was a bulltwang post anyway, but what friction is is the force opposing motion, and considering that the motion is downward during descending the friction be upwards.
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  • Martin318is

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    Re: Does bike weight really matter
    « Reply #7 on: May 23, 2012, 10:34 »
    When mates talk about ultralight components - such as bars and stems or wheels - I always ask: Would you be happy on that if you are on the brakes on a fast descent and hit a pothole?  In that case heavy ( by which I mean 'normal' is generally better.

    Personally I think once you're within say half a kg of the uci limit there is little sense in wasting money on lighter parts
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    just some guy

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    Re: Does bike weight really matter
    « Reply #8 on: May 23, 2012, 10:39 »
    most people could do well to lose a few kgs than worry too much about 500 grams by the by
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  • ram

    Re: Does bike weight really matter
    « Reply #9 on: May 23, 2012, 11:27 »
    Shan't matter for an amateur. With more tangible figures, the gains and losses could be calculated, but oh that's too hard to scour out and calculate now. My personal opinion, and you all know how much that's worth, is that it's like an amateur golfer spending around 20 or 30k US $ on a golf set when the stroke itself isn't perfect.
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  • Zam

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    Re: Does bike weight really matter
    « Reply #10 on: May 23, 2012, 11:41 »
    I dont think you can compare with golf  lol
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  • ram

    Re: Does bike weight really matter
    « Reply #11 on: May 23, 2012, 11:56 »
    Much more so than one realises, marginal gains are there in both, pretty much all, sports, and an amateur is an amateur because he's either not good enough or he's not practised enough. I could drive 10 yards further with a beaut, and I could ride much faster with a good bike, but it's still a question of whether it's worth the investment. Also, another weird thing is that expensive clubs are expensive because they're lighter and hit the ball longer. Much like the components on a bike.

    It's all about material engg, in one form or another. Then added to that are other stupid forms of engineering just to fry the brain.
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  • Dim

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    Re: Does bike weight really matter
    « Reply #12 on: May 23, 2012, 13:07 »
    having halved my bike weight going from a mountain bike to my kona, then yes..

    But 100g here and there.. dunno..
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  • ram

    Re: Does bike weight really matter
    « Reply #13 on: May 23, 2012, 15:47 »
    All that science is way too complex for me. But the one thing none of these sources mention is psychology. I think that accounts for a strong proportion of the argument in favour of less weight. You think you have even a small advantage and you ride to that effect. ;)
    In the case of descending-

    W*sin(a) in simplest terms is nothing but the effect of the weight along the incline.
    W*cos(a) is the effect of the weight in the direction perpendicular to the incline, it is known as normal reaction.

    Weight (W)= Mass* accn by gravity (which is 9.8 m/s^2)

    So, while descending, the effect of the weight along the incline opposes the friction.

    While climbing, friction and the weight act in the same direction. This is the flaw in the letter writer's plan, imo, he neglects the friction component along what is a small angle.

    As he has pointed out, the height is 20 and length is 100. The angle for this is pretty easy to find out with a calculator, tan inverse of (20/100), which is 11.3 degrees as he shows.

    Now the friction for this would be pretty considerable because F= uN, where u (the Greek letter mu)  is the coefficient of friction and will remain constant as long as the road and the tyre are the same. What's the issue? cos (11.3) is a pretty large value at .98 and ignoring that seems an error by him.

    Assuming coefficient of friction to be 0.3,
    F=uN
    where N is the normal reaction= W cos(a)=W cos(11.3)= 0.98*W

    F= 0.3 *0.98*W
    assuming 29 and 17lbs again,
    F(steel)=83.69lbs
    F(carbon)=49.01lbs
    and he has taken mass into a weight equation, thereby reducing the factor by 9.8
    so that difference has to be added too

    Let's also look at the inverse - though again I lack the scientific nous to answer the question - in terms of safety on long and technical descents, do lighter bike weights matter there too?
    Well, the fact is that during cornering, the speed of the bike has to reduce, that's a given. If a heavier bike is used, the force required to slow the bike down will increase. (Force= mass* acceleration/deceleration) I think that's a pointer to which could be safer for the purpose of descending.


    To summarise, a significant difference in weight like 12lbs could have an effect on the climbing and what not, but a few grams is pretty useless.
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  • « Last Edit: May 24, 2012, 03:48 by ram »

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    Re: Does bike weight really matter
    « Reply #14 on: May 23, 2012, 16:55 »
    You can bring all the science but when i ride i definitely can tell that bike weight matters.
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  • ram

    Re: Does bike weight really matter
    « Reply #15 on: May 23, 2012, 17:00 »
    And with that, I can say that in the case of performance, we aren't exactly in a position of disagreement. Finally, the other losses are all dependent on shape of the bike, the surface, the flow, the position, and many other factors, whose losses are harder to calculate and also mostly lesser than these friction losses, except in exceptional cases like blustery days or turbulent flows and such.

    But I stand by my original point that I can't find a massive issue by going ultra ultra light in comparison to ultra light, which was more in response to Martin's post.
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  • krabkakes

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    Re: Does bike weight really matter
    « Reply #16 on: May 23, 2012, 17:12 »
    I think it depends a lot on the weight of the rider. At 275lbs I would notice a 5lb increase in weight less than someone who weighs 125. My bikes range from 18lbs to 27lbs and I really don't notice the weight difference in them
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    Re: Does bike weight really matter
    « Reply #17 on: May 23, 2012, 17:44 »
    Aye, that could be because your legs would be used to producing higher forces for acceleration and higher work output, and a five pound increase isn't as big a difference percentage wise to the usual work you'd do for riding as in comparison to a person less than half that weight.
    By my knowledge,
    Work done= ∫F.ds where F is force and ds is the displacement differential and F is of course directly proportional to mass.

    Assuming both you and the lighter rider have the same instantaneous acceleration (for getting the Force), say a decent 10m/s^2, and taking the weights of the given carbon and steel bikes in the figure, over a paltry distance of 10m, you'd have a difference of percentage of work done as around 4.46% on the two bikes over the same distance and he'd have a 9.2% difference. Could well be that that's the discerning factor.
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  • Anthony Moan

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    Re: Does bike weight really matter
    « Reply #18 on: May 23, 2012, 19:31 »
    Of course it matter, but if someone has lighter bike and sorry ass training and other has steel monster with good training, last one would be faster. Spending money on lighter equipment is last resort, better to improve your diet, fitness, position etc. Of course we are humans and want to believe that spending money on lighter bike without training would make difference. I would like having lighter bike as possible.
    Like this article:

    How about spending money on a lighter bike? Cyclists love to spend money on lighter and the latest parts. The authors examined the effect of reducing bike weight from 10kg (~22 pounds) to 7kg (~14.5 pounds) on 40km TT performance. The effect is the N, W, and E cyclist improves by 13, 7 and 5 seconds, respectively.i Along those lines, losing 3 kg of body weight would reduce drag area by 1.84%. This reduction would improve 40km TT performance by 25, 21, and 19 seconds for the N, W, and E cyclist respectively.

    What about going uphill? Wouldn’t a lighter bike and/or weighing less make a difference? Of course! It is nice when science supports what we think to be true. On a 3% grade on a 20km TT, the authors determined that reducing bike weight by 3kg would result in a time savings of 94, 42 and 29 seconds for the N, W, and E cyclists. Increasing the grade to 6% yields savings of 3:38, 1:52, and 1:15 for the N, W, and E cyclists, respectively.

    http://www.cyclesportcoaching.com/Files/HowToSpendMoney.pdf
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    ram

    Re: Does bike weight really matter
    « Reply #19 on: May 24, 2012, 03:20 »
    I read the article, and I'd like to see more tangible figures than just time differences. Tangible being work output, power output and such because, while tested, it is just a few arbitrary numbers without the process being explained properly. Maybe that's a secret.


    Going back to this image, there's another issue with the question here. He assumes the weight of the bike only and does not take into consideration the weight of the rider at all. In the case he has pointed, he's basically pushing the bike up the incline and not climbing the incline on his bike, in which case, the mass of the rider would be added to the system and the difference would defo be higher.
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  • Anthony Moan

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    Re: Does bike weight really matter
    « Reply #20 on: May 24, 2012, 16:36 »
    I read the article, and I'd like to see more tangible figures than just time differences. Tangible being work output, power output and such because, while tested, it is just a few arbitrary numbers without the process being explained properly. Maybe that's a secret.
    Going back to this image, there's another issue with the question here. He assumes the weight of the bike only and does not take into consideration the weight of the rider at all. In the case he has pointed, he's basically pushing the bike up the incline and not climbing the incline on his bike, in which case, the mass of the rider would be added to the system and the difference would defo be higher.
    Brother, you know that I can not go into serious conversation with you :D, and you know that I suck in numbers over 24.
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  • ram

    Re: Does bike weight really matter
    « Reply #21 on: May 24, 2012, 16:40 »
    Ah, 37 is my limit, after that it's all Greek.
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  • Anthony Moan

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    Re: Does bike weight really matter
    « Reply #22 on: May 24, 2012, 16:47 »
    Ah, 37 is my limit, after that it's all Greek.
    Ah no no no, you math wizard. I know you are working on Indian space program and nukes.
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  • ram

    Re: Does bike weight really matter
    « Reply #23 on: May 24, 2012, 17:09 »
    Sshhh.... Cleaning posts are very rare, I don't want competition.
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  • usedtobefast

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    Re: Does bike weight really matter
    « Reply #24 on: May 31, 2012, 02:43 »
    you will go faster on a lighter bike. how is this even a debate? think about the physics. moving heavier takes more effort. less weight,less effort.
    not just some guess work. light wheels really help.
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  • usedtobefast

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    Re: Does bike weight really matter
    « Reply #25 on: May 31, 2012, 02:53 »
    You can bring all the science but when i ride i definitely can tell that bike weight matters.
    my 32 pound mtn bike takes me 10 minutes longer each way versus my old school 20 pound road bike.
    the effort "feels" the same. my modern race bike? it knocks off another 5 each way.
    but by all means ride heavy or ride light, just ride.
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  • Anthony Moan

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    Re: Does bike weight really matter
    « Reply #26 on: May 31, 2012, 14:52 »
    Ok lets put aside math and physics ;D
    What is faster?
    1. Old 190d Mercedes with four Albanians trying to smuggle 500kg of heroin in Italy or;
    2. Old 190d Mercedes with only one Albanian driving and no heroin
    If someone knows what I am talking about ;D


     
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    Re: Does bike weight really matter
    « Reply #27 on: May 31, 2012, 19:53 »
    Ok lets put aside math and physics ;D
    What is faster?
    1. Old 190d Mercedes with four Albanians trying to smuggle 500kg of heroin in Italy or;
    2. Old 190d Mercedes with only one Albanian driving and no heroin
    If someone knows what I am talking about ;D

    black tar or china white?
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  • Anthony Moan

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    Re: Does bike weight really matter
    « Reply #28 on: May 31, 2012, 21:10 »
    black tar or china white?
    Afghan No. 3 ;D
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